publications | Savvas Raptis

2026

Time-invariant properties and principal components of in-situ measurements used for outlier detection in space missions

J. Ekelund, S. Raptis, V. Toy-Edens, W. Mo, D.L. Turner, I.J. Cohen, and S. Markidis

Journal of Computational Science, 2026

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Understanding Earth’s magnetosphere requires analyzing complex, multiscale interactions captured through diverse in-situ measurements such as particle distributions (e.g., ion spectra and flow velocities), and electromagnetic fields. Modern space missions, including NASA’s MMS and THEMIS, produce large volumes of such time-series data, where scientifically relevant events often appear as short-lived, context-dependent outliers. In this work, we investigate the structure of time-windowed, multi-feature datasets from Earth’s magnetosphere and show that their information content can be effectively represented using a reduced set of largely time-invariant principal components. Using Principal Component Analysis (PCA) for static datasets and Incremental PCA for streaming observations, we characterize these components and leverage the associated reconstruction error to develop an unsupervised outlier detection method suitable for evolving data distributions. Building on our earlier approach, this method robustly identifies significant plasma phenomena in both structured and streaming-mode measurements. Applied to MMS and THEMIS observations, it successfully recovers known events, including bow shock and magnetopause crossings, foreshock transients, and plasma bubbles, while also highlighting additional scientifically relevant structures. This demonstrates that dimensionality-reduction-based outlier detection provides an effective pathway for automated event identification in complex space plasma datasets. This is an extension of previous work presented in Ekelund et al. (2025).
APA

Ekelund, J., Raptis, S., Toy-Edens, V., Mo, W., Turner, D. L., Cohen, I. J., Markidis, S.(2026). Time-invariant properties and principal components of in-situ measurements used for outlier detection in space missions. Journal of Computational Science. https://doi.org/https://doi.org/10.1016/j.jocs.2026.102855

BibTeX
```
@article{Ekelund_2026,
  title = {Time-invariant properties and principal components of in-situ measurements used for outlier detection in space missions},
  journal = {Journal of Computational Science},
  pages = {102855},
  year = {2026},
  issn = {1877-7503},
  doi = {https://doi.org/10.1016/j.jocs.2026.102855},
  url = {https://www.sciencedirect.com/science/article/pii/S1877750326000736},
  author = {Ekelund, Jonah and Raptis, Savvas and Toy-Edens, Vicki and Mo, Wenli and Turner, Drew L. and Cohen, Ian J. and Markidis, Stefano},
  keywords = {Outlier detection, Incremental PCA, In-site time series measurements, Online learning}
}
```
Compressive Structures in the Foreshock of Collisionless Shocks

S. Raptis, D. Trotta, D.L. Turner, X. Blanco-Cano, H. Hietala, T. Karlsson, I.C. Jebaraj, I.Y. Vasko, A. Osmane, K. Takahashi, and 4 more authors

The Astrophysical Journal Letters, Mar 2026

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Collisionless shocks are fundamental accelerators of energetic particles, yet the observations of nonlinear foreshock structures, which are essential in acceleration processes, differ significantly between interplanetary (IP) shocks and planetary bow shocks. We present a direct comparison of two high-Mach-number, quasi-parallel shocks: an IP shock observed by Solar Orbiter and the Earth’s bow shock measured by the Magnetospheric Multiscale mission during the 2024–2025 “string-of-pearls” campaign. We show that foreshock compressive structures (FCSs) initiate upstream of both shocks at similar normalized distances (≲50 ion inertial lengths, di) when the suprathermal (>10 keV) ion density exceeds ∼1% of the background. However, the IP shock lacks the fully evolved, high-amplitude short large-amplitude magnetic structures characteristic of the terrestrial foreshock. We demonstrate that the “growth zone” capable of sustaining these structures is spatially limited (∼135 di), which, due to the high speed of the propagating IP shock, corresponds to a brief observational window of <10 s. Beyond this observational constraint, we suggest an additional physical mechanism that can inhibit foreshock maturity at IP shocks. The lack of global curvature prevents the lateral supply (“cross talk”) of energetic ions from different shock regions. These findings suggest that while the fundamental physics of FCS initiation is unified across collisionless shocks, the achievement of full nonlinearity can be regulated by the unique shock geometry and upstream properties while ultimately remaining observationally challenging to identify.
APA

Raptis, S., Trotta, D., Turner, D. L., Blanco-Cano, X., Hietala, H., Karlsson, T., Jebaraj, I. C., Vasko, I. Y., Osmane, A., Takahashi, K., Lario, D., Wilson, L. B., Howes, G. G., Wimmer-Schweingruber, R. F.(2026). Compressive Structures in the Foreshock of Collisionless Shocks. The Astrophysical Journal Letters. https://doi.org/10.3847/2041-8213/ae53e5

BibTeX
```
@article{Raptis_2026apjl,
  doi = {10.3847/2041-8213/ae53e5},
  url = {https://doi.org/10.3847/2041-8213/ae53e5},
  year = {2026},
  month = mar,
  publisher = {The American Astronomical Society},
  volume = {1000},
  number = {2},
  pages = {L55},
  author = {Raptis, Savvas and Trotta, Domenico and Turner, Drew L. and Blanco-Cano, Xóchitl and Hietala, Heli and Karlsson, Tomas and Jebaraj, Immanuel Christopher and Vasko, Ivan Y. and Osmane, Adnane and Takahashi, Kazue and Lario, David and Wilson, Lynn B. and Howes, Gregory G. and Wimmer-Schweingruber, Robert F.},
  title = {Compressive Structures in the Foreshock of Collisionless Shocks},
  journal = {The Astrophysical Journal Letters}
}
```
Universal energy limits of radiation belts in planetary and brown dwarf magnetospheric systems

D.L. Turner, S. Raptis, A. Osmane, A. Egan, G. Clark, T. Nordheim, L. Regoli, and A.Y. Ukhorskiy

Science Advances, Mar 2026

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Radiation belts are regions of magnetically trapped particle radiation found around all of the sufficiently magnetized planets in the Solar System and recently also observed around brown dwarfs, yet despite their ubiquity, there is not yet a general theory or model to predict the uppermost energy limits that any particular magnetospheric system’s radiation belts can attain. By considering only the most fundamental loss processes, a model and corresponding theory are developed that successfully bound and explain the maximum observed energies of all documented radiation belt systems. This approach yields a relatively simple function for the uppermost energy limit that depends on only the surface magnetic field strength of the system. The model predicts an energy limit for all radiation belt systems that asymptotes at 7 ± 2 teraelectronvolts (TeV) (for protons and electrons), offering intriguing, previously unrecognized insight on potential sources of galactic cosmic rays. This model is also applied to an exoplanetary system, demonstrating that the planet is likely a synchrotron emitter and showcasing the model’s use for identifying candidate targets for synchrotron-emitting astrophysical systems and revealing details critical to habitability at those remote worlds.
@article{10_1126_sciadv_aea4945, title = {Universal energy limits of radiation belts in planetary and brown dwarf magnetospheric systems}, author = {Turner, D. L. and Raptis, S. and Osmane, A. and Egan, A. and Clark, G. and Nordheim, T. and Regoli, L. and Ukhorskiy, A. Y.}, journal = {Science Advances}, year = {2026}, doi = {10.1126/sciadv.aea4945}, url = {https://doi.org/10.1126/sciadv.aea4945}, }
APA

Turner, D. L., Raptis, S., Osmane, A., Egan, A., Clark, G., Nordheim, T., Regoli, L., Ukhorskiy, A. Y.(2026). Universal energy limits of radiation belts in planetary and brown dwarf magnetospheric systems. Science Advances. https://doi.org/10.1126/sciadv.aea4945

BibTeX
```
@article{10_1126_sciadv_aea4945,
  title = {Universal energy limits of radiation belts in planetary and brown dwarf magnetospheric systems},
  author = {Turner, D. L. and Raptis, S. and Osmane, A. and Egan, A. and Clark, G. and Nordheim, T. and Regoli, L. and Ukhorskiy, A. Y.},
  journal = {Science Advances},
  year = {2026},
  doi = {10.1126/sciadv.aea4945},
  url = {https://doi.org/10.1126/sciadv.aea4945},
}
```
Relationship between magnetosheath ULF waves and ground-based Pc3-4 waves: A statistical study

T.Z. Liu, V. Angelopoulos, S. Dorfman, M.D. Hartinger, S. Raptis, K. Zhang, and S. Zhao

Journal of Geophysical Research: Space Physics, Mar 2026

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Foreshock ultralow frequency (ULF) waves are a major contributor to magnetospheric Pc3–4 waves (7–100 mHz), but their transmission through the magnetosheath is not well understood. Using 109 THEMIS traversals from the bow shock to the magnetopause, in conjunction with ground magnetometer (GMAG) measurements, we performed a statistical analysis of magnetosheath ULF waves and their relationship to ground-based Pc3–4 waves. Our findings reveal that in quasi-parallel regions, magnetic and dynamic pressure wave power are correlated with ground-based magnetic wave power at periods of ∼30s, with correlation coefficients reaching up to ∼0.7. The correlation depends on the THEMIS spacecraft’s position in the magnetosheath as well as the magnetic local time and latitude of the ground stations. In contrast, in quasi-perpendicular regions, the correlation is weaker (up to ∼0.3) and increases with decreasing frequency. Additionally, in quasi-perpendicular regions, wave power increases from the bow shock to the magnetopause, consistent with local excitation, whereas waves in quasi-parallel regions are less compressive with power relatively stable, consistent with a foreshock origin. Our results suggest that foreshock-originated waves in quasi-parallel regions contribute more effectively to magnetospheric ULF waves than those in quasi-perpendicular regions, through both magnetic field and dynamic pressure oscillations, with a preferential propagation from the dawnside magnetosheath to both sides of the magnetosphere.
@article{10_1029_2025ja034763, title = {Relationship between magnetosheath ULF waves and ground-based Pc3-4 waves: A statistical study}, author = {Liu, T. Z. and Angelopoulos, V. and Dorfman, S. and Hartinger, M. D. and Raptis, S. and Zhang, K. and Zhao, S.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2026}, doi = {10.1029/2025JA034763}, url = {https://doi.org/10.1029/2025JA034763}, }
APA

Liu, T. Z., Angelopoulos, V., Dorfman, S., Hartinger, M. D., Raptis, S., Zhang, K., Zhao, S.(2026). Relationship between magnetosheath ULF waves and ground-based Pc3-4 waves: A statistical study. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA034763

BibTeX
```
@article{10_1029_2025ja034763,
  title = {Relationship between magnetosheath ULF waves and ground-based Pc3-4 waves: A statistical study},
  author = {Liu, T. Z. and Angelopoulos, V. and Dorfman, S. and Hartinger, M. D. and Raptis, S. and Zhang, K. and Zhao, S.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2026},
  doi = {10.1029/2025JA034763},
  url = {https://doi.org/10.1029/2025JA034763},
}
```
Energy partition at a collisionless supercritical quasi-parallel shock

S.J. Schwartz, K.J. Trattner, S. Raptis, R.E. Ergun, L.B.W. III, R.G. Gomez, I.J. Cohen, D.J. Gershman, K.A. Goodrich, H. Kucharek, and 1 more author

Journal of Geophysical Research: Space Physics, Mar 2026

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Shocks in collisionless astrophysical plasmas redistribute some of the incident flow energy into both thermal and non-thermal energy. Quantifying the partition of that energy amongst various particle species or their sub-populations, and electromagnetic energy, represents a fundamental goal of shock physics. It embodies the role of the equation of state for the system. Here we apply a framework to assess all the incident and downstream energy fluxes at a crossing of Earth’s bow shock for which the upstream magnetic field was roughly aligned with the shock normal direction. Such quasi-parallel shocks are known to be non-steady and to produce significant populations of suprathermal particles. We quantify the evolution of all the important carriers of energy flux through the shock region. We sub-divide the proton population into thermal, suprathermal, and energetic components in order to investigate the shock’s efficiency in energizing the nonthermal particles. While the largest energy fluxes are found in the incident proton ram energy and downstream proton thermal enthalpy fluxes, a significant suprathermal population pervades the regions both up- and downstream. We also evaluate the energy fluxes attributable to fluctuations in the fluid and field parameters.
@article{10_1029_2025ja034718, title = {Energy partition at a collisionless supercritical quasi-parallel shock}, author = {Schwartz, S. J. and Trattner, K. J. and Raptis, S. and Ergun, R. E. and III, L. B. Wilson and Gomez, R. G. and Cohen, I. J. and Gershman, D. J. and Goodrich, K. A. and Kucharek, H. and Vo, T.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2026}, doi = {10.1029/2025JA034718}, url = {https://doi.org/10.1029/2025JA034718}, }
APA

Schwartz, S. J., Trattner, K. J., Raptis, S., Ergun, R. E., III, L. B. W., Gomez, R. G., Cohen, I. J., Gershman, D. J., Goodrich, K. A., Kucharek, H., Vo, T.(2026). Energy partition at a collisionless supercritical quasi-parallel shock. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA034718

BibTeX
```
@article{10_1029_2025ja034718,
  title = {Energy partition at a collisionless supercritical quasi-parallel shock},
  author = {Schwartz, S. J. and Trattner, K. J. and Raptis, S. and Ergun, R. E. and III, L. B. Wilson and Gomez, R. G. and Cohen, I. J. and Gershman, D. J. and Goodrich, K. A. and Kucharek, H. and Vo, T.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2026},
  doi = {10.1029/2025JA034718},
  url = {https://doi.org/10.1029/2025JA034718},
}
```
Statistical Characteristics of Stormtime Bursty Bulk Flows

A.P. Devanandan, A. Keesee, S. Raptis, S. Ohtani, V. Merkin, and M. Gkioulidou

Geophysical Research Letters, Mar 2026

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Bursty bulk flows (BBFs) play a significant role in transporting plasma earthward in the magnetotail. While their properties have been extensively studied, their behavior during geomagnetic storms needs further understanding. In this study, we investigate the stormtime characteristics of BBFs, and compare them to non‐stormtime, by performing a superposed epoch analysis using data from ISAS/NASA’s Geotail mission. Our results show that the properties of BBFs during stormtime and non‐stormtime remain largely consistent relative to the background plasma sheet conditions. The convection electric field is higher for stormtime BBFs which is primarily associated with an elevated magnetic field in the plasma sheet during storms. Moreover, stormtime plasma sheet conditions, such as an enhanced magnetic field and an elevated ion temperature, are reflected in the properties of BBFs indicating the strong influence of the background plasma environment on BBF dynamics.
@article{10_1029_2025gl119632, title = {Statistical Characteristics of Stormtime Bursty Bulk Flows}, author = {Devanandan, A. P. and Keesee, A. and Raptis, S. and Ohtani, S. and Merkin, V. and Gkioulidou, M.}, journal = {Geophysical Research Letters}, year = {2026}, doi = {10.1029/2025GL119632}, url = {https://doi.org/10.1029/2025GL119632}, }
APA

Devanandan, A. P., Keesee, A., Raptis, S., Ohtani, S., Merkin, V., Gkioulidou, M.(2026). Statistical Characteristics of Stormtime Bursty Bulk Flows. Geophysical Research Letters. https://doi.org/10.1029/2025GL119632

BibTeX
```
@article{10_1029_2025gl119632,
  title = {Statistical Characteristics of Stormtime Bursty Bulk Flows},
  author = {Devanandan, A. P. and Keesee, A. and Raptis, S. and Ohtani, S. and Merkin, V. and Gkioulidou, M.},
  journal = {Geophysical Research Letters},
  year = {2026},
  doi = {10.1029/2025GL119632},
  url = {https://doi.org/10.1029/2025GL119632},
}
```
Reconstructing the geometry of a hot flow anomaly with bounding jets in magnetosheath

Y. Zhou, B. Wang, S. Raptis, S. Wang, J. Guo, J.H. Shue, D. Sibeck, L.Q. Lu, J. Zhang, C. Shen, and 4 more authors

Geophysical Research Letters, Mar 2026

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When interplanetary magnetic field discontinuities interact with planetary bow shocks, hot flow anomalies (HFAs) form in the solar wind and can extend into the magnetosheath. Here we reconstruct the three-dimensional geometry of an HFA bounded by two jet regions in the terrestrial magnetosheath. Using a previously established conceptual model of HFA evolution together with in situ measurements in the magnetosheath and pristine solar wind, we derive the structure’s geometrical characteristics and show that its normal aligns with the discontinuity normal. It spans most of the dayside magnetosheath. Ground magnetometer data corroborate the reconstruction, revealing both the scale of the disturbance and its dusk-to-dawn propagation. Notably, one bounding jet reaches 11 in width, significantly larger than the sizes of typical magnetosheath jets reported in the literature.
@article{10_1029_2025gl119404, title = {Reconstructing the geometry of a hot flow anomaly with bounding jets in magnetosheath}, author = {Zhou, Y. and Wang, B. and Raptis, S. and Wang, S. and Guo, J. and Shue, J.-H. and Sibeck, D. and Lu, L. Q. and Zhang, J. and Shen, C. and Kieokaew, R. and Escoubet, C. P. and Shao, P. and Burch, J.}, journal = {Geophysical Research Letters}, year = {2026}, doi = {10.1029/2025GL119404}, url = {https://doi.org/10.1029/2025GL119404}, }
APA

Zhou, Y., Wang, B., Raptis, S., Wang, S., Guo, J., Shue, J., Sibeck, D., Lu, L. Q., Zhang, J., Shen, C., Kieokaew, R., Escoubet, C. P., Shao, P., Burch, J.(2026). Reconstructing the geometry of a hot flow anomaly with bounding jets in magnetosheath. Geophysical Research Letters. https://doi.org/10.1029/2025GL119404

BibTeX
```
@article{10_1029_2025gl119404,
  title = {Reconstructing the geometry of a hot flow anomaly with bounding jets in magnetosheath},
  author = {Zhou, Y. and Wang, B. and Raptis, S. and Wang, S. and Guo, J. and Shue, J.-H. and Sibeck, D. and Lu, L. Q. and Zhang, J. and Shen, C. and Kieokaew, R. and Escoubet, C. P. and Shao, P. and Burch, J.},
  journal = {Geophysical Research Letters},
  year = {2026},
  doi = {10.1029/2025GL119404},
  url = {https://doi.org/10.1029/2025GL119404},
}
```

2025

The correlation function for magnetic field fluctuations at ion dissipation scales in the solar wind.

A.J. Angeles, H.E. Spence, C.W. Smith, B.J. Vasquez, I.J. Cohen, K.J. Genestreti, R. Skoug, S. Raptis, C. Gabrielse, D.J. Gershman, and 1 more author

Journal of Geophysical Research: Space Physics, Mar 2025

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This study investigates energy dissipation in small-scale solar wind turbulence using a novel approach to autocorrelation function analysis leveraging high-resolution data from the Magnetospheric Multiscale Mission (MMS). We analyze magnetic field fluctuations at ion dissipation scales, focusing on short 20-s intervals to isolate dissipation-scale dynamics. Using MMS’s fluxgate magnetometer, fast plasma investigation, and energetic particle detector, we compute normalized correlation functions as functions of the interplanetary magnetic field cone angle. Our results show that turbulence is correlated over short spatial scales (100–1,000 km), with shorter correlation lengths in the compressional component compared to the transverse components. We find that the transverse correlation lengths differ most when the interplanetary magnetic field is nearly perpendicular to the solar wind flow (cone angle ), and that they vary approximately as the inverse sine of the cone angle. The characteristics of the correlation length suggest that the turbulence observed is primarily two-dimensional. These findings highlight the anisotropic nature of dissipation-scale turbulence and its dependence on solar wind conditions, providing insights into energy transfer in space plasmas.
@article{10_1029_2025ja034569, title = {The correlation function for magnetic field fluctuations at ion dissipation scales in the solar wind.}, author = {Angeles, Alvin JG and Spence, Harlan E and Smith, Charles W and Vasquez, Bernard J and Cohen, Ian J and Genestreti, Kevin J and Skoug, Ruth and Raptis, Savvas and Gabrielse, Christine and Gershman, Daniel J and others}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA034569}, url = {https://doi.org/10.1029/2025JA034569}, }
APA

Angeles, A. J., Spence, H. E., Smith, C. W., Vasquez, B. J., Cohen, I. J., Genestreti, K. J., Skoug, R., Raptis, S., Gabrielse, C., Gershman, D. J., others,(2025). The correlation function for magnetic field fluctuations at ion dissipation scales in the solar wind.. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA034569

BibTeX
```
@article{10_1029_2025ja034569,
  title = {The correlation function for magnetic field fluctuations at ion dissipation scales in the solar wind.},
  author = {Angeles, Alvin JG and Spence, Harlan E and Smith, Charles W and Vasquez, Bernard J and Cohen, Ian J and Genestreti, Kevin J and Skoug, Ruth and Raptis, Savvas and Gabrielse, Christine and Gershman, Daniel J and others},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA034569},
  url = {https://doi.org/10.1029/2025JA034569},
}
```
Stormtime Magnetospheric Processes Associated with the Dawnside Current Wedge

S. Ohtani, S. Raptis, S. Devanandan, T. Motoba, Y. Zou, J.W. Gjerloev, and V.G. Merkin

Journal of Geophysical Research: Space Physics, Mar 2025

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The intensification of the westward auroral electrojet (AEJ) in the dawn sector is a characteristic feature of the storm main phase. It is considered an ionospheric segment of a wedge‐type current system, the dawnside current wedge (DCW), formed by the disruption (short‐circuiting through the ionosphere) of a magnetospheric equatorial current. The present study observationally investigates associated magnetospheric processes with a focus on near‐Earth dipolarization and tail magnetic reconnection. It is found that as the dawnside AEJ intensifies, (a) geosynchronous magnetic field dipolarizes in the dawn sector, with its region expanding eastward from the nightside, and (b) tail reconnection becomes active in the dawnside plasma sheet, with an X line retreating tailward as suggested by negative‐to‐positive transitions of V⊥,X and Bz. (a) suggests that the DCW initially develops as a substorm current wedge expanding from the nightside. (b) implies that the corresponding dipolarization region expands dawnward as earthward reconnection outflows transport magnetic flux from the plasma sheet. It is suggested that the DCW develops following an enhancement of ionospheric conductance due to the precipitation of energetic electrons, which drift eastward after being injected by a nightside substorm. As the magnetic configuration becomes more dipolar, earthward reconnection outflows may be deflected farther dawnward, which possibly sustains the dawnward expansion of the DCW. At the same time, however, the pile‐up of magnetic flux may lead to the retreat of the X line. Therefore, the DCW likely evolves as a consequence of a complex two‐way coupling between the near‐Earth current reduction and tail reconnection.
@article{10_1029_2025ja034418, title = {Stormtime Magnetospheric Processes Associated with the Dawnside Current Wedge}, author = {Ohtani, S. and Raptis, S. and Devanandan, S. and Motoba, T. and Zou, Y. and Gjerloev, J. W. and Merkin, V. G.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA034418}, url = {https://doi.org/10.1029/2025JA034418}, }
APA

Ohtani, S., Raptis, S., Devanandan, S., Motoba, T., Zou, Y., Gjerloev, J. W., Merkin, V. G.(2025). Stormtime Magnetospheric Processes Associated with the Dawnside Current Wedge. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA034418

BibTeX
```
@article{10_1029_2025ja034418,
  title = {Stormtime Magnetospheric Processes Associated with the Dawnside Current Wedge},
  author = {Ohtani, S. and Raptis, S. and Devanandan, S. and Motoba, T. and Zou, Y. and Gjerloev, J. W. and Merkin, V. G.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA034418},
  url = {https://doi.org/10.1029/2025JA034418},
}
```
Energy Conversion and Exchange in a Magnetosheath Jet

O.W. Roberts, Z. Voros, A. Settino, F. Koller, S. Raptis, M. Temmer, and al.

Journal of Geophysical Research: Space Physics, Mar 2025

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Magnetosheath jets are regions with an extremely large dynamic pressure compared to that of the background plasma. We present a case study of a magnetosheath jet examining energy conversion processes and its interaction with the surrounding magnetosheath plasma. To understand the energy conversion processes we use data from the Magnetospheric Multiscale mission (MMS) to calculate the scalar product of the total current density J and the electric field (in the electron flow rest frame) Eʹ and the pressure strain interaction term Large energy conversion between the fields and flow is observed at the leading edge of the jetwhere a flow reversal and a strong current is observed. The Walén test suggests that magnetic reconnection may also occur in this region. Significant heating of the electrons through the compressive channel is observed. Within the jet itself, the plasma is cooling, indicative of an expansion of the jet as it evolves. The non‐ Maxwellianity of the ion and electron velocity distribution functions are calculated using three different measures. The non‐Maxwellianity shows spikes for the electrons near the reconnection site, while ions exhibit higher non‐Maxwellianity at the front of the jet and a smaller value near the peak of the dynamic pressure. Electrons and ions show similar trends with a time delay, suggesting a relationship between the non‐ Maxwellianity, indicating the different scale sizes present for both species
@article{10_1029_2025ja034414, title = {Energy Conversion and Exchange in a Magnetosheath Jet}, author = {Roberts, O. W. and Voros, Z. and Settino, A. and Koller, F. and Raptis, S. and Temmer, M. and et al.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA034414}, url = {https://doi.org/10.1029/2025JA034414}, }
APA

Roberts, O. W., Voros, Z., Settino, A., Koller, F., Raptis, S., Temmer, M., al.,(2025). Energy Conversion and Exchange in a Magnetosheath Jet. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA034414

BibTeX
```
@article{10_1029_2025ja034414,
  title = {Energy Conversion and Exchange in a Magnetosheath Jet},
  author = {Roberts, O. W. and Voros, Z. and Settino, A. and Koller, F. and Raptis, S. and Temmer, M. and et al.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA034414},
  url = {https://doi.org/10.1029/2025JA034414},
}
```
A Comparison of Modeled and Observed Dayside Bow Shock Locations in 8 Years of MMS Data

W. Mo, S. Raptis, V. Toy‐Edens, K. Yeakel, and D.L. Turner

Journal of Geophysical Research: Space Physics, Mar 2025

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The interplay between Earth’s magnetic field and the solar wind provides a natural laboratory to study the physics of shock waves in collisionless plasmas. 3D parameterized shape models of Earth’s bow shock boundary quantify how this interaction depends on upstream solar wind parameters. Using 2,063 bow shocks observed with the Magnetospheric Multiscale (MMS) mission over 8 years, we investigate the relationship between the observed and parameterized bow shock location with solar wind parameters. We find that the observed bow shock location is strongly correlated with the solar wind density, plasma β, and Mach number. In addition, we provide updated fitting parameters to bow shock models from literature derived empirically or using magnetohydrodynamic (MHD) simulations. Models provide a reasonable fit to the data after updating the fit with MMS‐observed bow shocks, with coefficient of determination (R2) scores between 0.836 0.878. However, we find that observed locations can still deviate significantly from model predictions under extreme solar wind conditions. We also explore the models’ variability under different interplanetary magnetic field (IMF) clock angles (Northward and Southward) and shock geometries (quasi‐perpendicular and quasi‐parallel). While we observe no discernible difference in the bow shock shape as a function of IMF direction, we find that quasi‐parallel bow shocks are systematically closer to Earth than quasi‐perpendicular, with a disparity of as much as ∼ 1 RE in bow shock stand‐off distance between the two bow shock types
@article{10_1029_2025ja033966, title = {A Comparison of Modeled and Observed Dayside Bow Shock Locations in 8 Years of MMS Data}, author = {Mo, W. and Raptis, S. and Toy‐Edens, V. and Yeakel, K. and Turner, D. L.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA033966}, url = {https://doi.org/10.1029/2025JA033966}, }
APA

Mo, W., Raptis, S., Toy‐Edens, V., Yeakel, K., Turner, D. L.(2025). A Comparison of Modeled and Observed Dayside Bow Shock Locations in 8 Years of MMS Data. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA033966

BibTeX
```
@article{10_1029_2025ja033966,
  title = {A Comparison of Modeled and Observed Dayside Bow Shock Locations in 8 Years of MMS Data},
  author = {Mo, W. and Raptis, S. and Toy‐Edens, V. and Yeakel, K. and Turner, D. L.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA033966},
  url = {https://doi.org/10.1029/2025JA033966},
}
```
Automated Bow Shock Identification and Multi‐Spacecraft Timing Using Magnetospheric Multiscale (MMS) Observations

V. Toy‐Edens, S. Raptis, D.L. Turner, W. Mo, and S.A.Q. Young

Journal of Geophysical Research: Space Physics, Mar 2025

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Utilizing 8 years of dayside Magnetospheric Multiscale (MMS) mission plasma region identifications, we present an automatically identified and manually verified data set of 2,594 bow shock crossings in MMS burst‐mode. For each bow shock crossing, we identify the bow shock ramp in each MMS probe using two automated methods and apply multi‐spacecraft timing to calculate the bow shock normal. The bow shock list was separated into quasi‐parallel and quasi‐perpendicular based on the presence or absence of ion foreshock in order to evaluate deviations between the automated methods and a statistical 3D bow shock model. There are large discrepancies between global and local shock properties where the local shock properties are highly skewed towards quasi‐perpendicular properties regardless of the presence of ion foreshock. Although this skewness grows when the tetrahedral configuration is suboptimal, it persists even under ideal formation, indicating that electron‐scale processes can modulate local shock properties. These findings highlight the limitations of local multi‐spacecraft timing in accurately characterizing shock geometry without contextual information, such as the presence of an upstream foreshock or a similarly disturbed downstream magnetosheath. Ultimately, this data article provides thousands of high‐resolution bow shock crossings for further scientific research by the community.
@article{10_1029_2025ja034252, title = {Automated Bow Shock Identification and Multi‐Spacecraft Timing Using Magnetospheric Multiscale (MMS) Observations}, author = {Toy‐Edens, V. and Raptis, S. and Turner, D. L. and Mo, W. and Young, S. A. Q.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA034252}, url = {https://doi.org/10.1029/2025ja034252}, }
APA

Toy‐Edens, V., Raptis, S., Turner, D. L., Mo, W., Young, S. A. Q.(2025). Automated Bow Shock Identification and Multi‐Spacecraft Timing Using Magnetospheric Multiscale (MMS) Observations. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA034252

BibTeX
```
@article{10_1029_2025ja034252,
  title = {Automated Bow Shock Identification and Multi‐Spacecraft Timing Using Magnetospheric Multiscale (MMS) Observations},
  author = {Toy‐Edens, V. and Raptis, S. and Turner, D. L. and Mo, W. and Young, S. A. Q.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA034252},
  url = {https://doi.org/10.1029/2025ja034252},
}
```
On the Spatial Relationship Between the Aurora and Relativistic Electron Precipitation During a Storm‐Time Substorm

M. Shumko, A. Artemyev, S. Raptis, Y. Zou, D.L. Turner, A.Y. Ukhorskiy, C. Gabrielse, G.K. Stephens, I.J. Cohen, C. Wilkins, and 10 more authors

Geophysical Research Letters, Mar 2025

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During substorms, Earth’s magnetotail undergoes rapid dipolarization, driving Earthward plasma flows that decelerate and dissipate energy upon encountering the dipole magnetic field in the nightside transition region. This region mediates the interaction between the magnetotail, inner magnetosphere, and the ionospheric auroral zone, though significant mapping uncertainties obscure the precise link and particle acceleration processes. Using data from THEMIS, TREx, and ELFIN, we analyze a storm‐time substorm on 4 September 2022, establishing a relationship, that is, not a causation, between magnetospheric and ionospheric dynamics. Following a dipolarization, the auroral bulge overlapped with the footprints of the electron isotropy boundary (IB) and the outer radiation belt. Notably, the precipitating electron energies reached at least 2 MeV in the bulge, exceeding previous reports. By comparing the latitudes of the electron IB with respect to the auroral bulge, we deduce that the sources of both auroral and relativistic precipitation were confined in the dipolarized region.
@article{10_1029_2025gl116477, title = {On the Spatial Relationship Between the Aurora and Relativistic Electron Precipitation During a Storm‐Time Substorm}, author = {Shumko, M. and Artemyev, A. and Raptis, S. and Zou, Y. and Turner, D. L. and Ukhorskiy, A. Y. and Gabrielse, C. and Stephens, G. K. and Cohen, I. J. and Wilkins, C. and Tsai, E. and Ohtani, S. and Gallardo‐Lacourt, B. and Sorathia, K. and Sergeev, V. and Gjerloev, J. W. and Donovan, E. and Spanswick, E. and Angelopoulos, V. and Jaynes, A. N.}, journal = {Geophysical Research Letters}, year = {2025}, doi = {10.1029/2025GL116477}, url = {https://doi.org/10.1029/2025gl116477}, }
APA

Shumko, M., Artemyev, A., Raptis, S., Zou, Y., Turner, D. L., Ukhorskiy, A. Y., Gabrielse, C., Stephens, G. K., Cohen, I. J., Wilkins, C., Tsai, E., Ohtani, S., Gallardo‐Lacourt, B., Sorathia, K., Sergeev, V., Gjerloev, J. W., Donovan, E., Spanswick, E., Angelopoulos, V., Jaynes, A. N.(2025). On the Spatial Relationship Between the Aurora and Relativistic Electron Precipitation During a Storm‐Time Substorm. Geophysical Research Letters. https://doi.org/10.1029/2025GL116477

BibTeX
```
@article{10_1029_2025gl116477,
  title = {On the Spatial Relationship Between the Aurora and Relativistic Electron Precipitation During a Storm‐Time Substorm},
  author = {Shumko, M. and Artemyev, A. and Raptis, S. and Zou, Y. and Turner, D. L. and Ukhorskiy, A. Y. and Gabrielse, C. and Stephens, G. K. and Cohen, I. J. and Wilkins, C. and Tsai, E. and Ohtani, S. and Gallardo‐Lacourt, B. and Sorathia, K. and Sergeev, V. and Gjerloev, J. W. and Donovan, E. and Spanswick, E. and Angelopoulos, V. and Jaynes, A. N.},
  journal = {Geophysical Research Letters},
  year = {2025},
  doi = {10.1029/2025GL116477},
  url = {https://doi.org/10.1029/2025gl116477},
}
```
Statistical Relationship Between Foreshock ULF Wave Power and Ground‐Based Pc3‐4 Wave Power

T.Z. Liu, V. Angelopoulos, S. Dorfman, M.D. Hartinger, K. Zhang, S. Raptis, and D. Ma

Journal of Geophysical Research: Space Physics, Mar 2025

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Magnetospheric ultralow frequency (ULF) waves are fundamental for coupling energy across the magnetosphere and ionosphere. Pc3‐4 waves (7–100 mHz) are associated with small interplanetary magnetic field (IMF) cone angles, suggesting that foreshock ULF waves are the source. To understand the relationship between foreshock and magnetospheric ULF waves, we perform a statistical study using the THEMIS spacecraft to observe foreshock ULF waves and ground magnetometers (GMAG) to infer magnetospheric ULF waves. We observe a power law correlation between foreshock and ground‐based ULF wave power, with correlation coefficients exceeding 0.5 around the typical period of foreshock “30s waves” in contrast to correlation coefficients ∼0.3 between solar wind and ground‐based ULF wave power. The power law parameters decrease with lower magnetic latitudes, indicating weaker power transport deeper in the magnetosphere. Additionally, the correlation coefficients decrease with larger magnetic local time (MLT) separation between the THEMIS spacecraft and GMAG. We also find that ground‐based Pc3‐4 wave power exhibits a stronger dependence on the local bow shock θBn (angle between the shock normal and the IMF) than on the IMF cone angle. These findings indicate that foreshock ULF waves are more likely to be transmitted from the local MLT than across the subsolar point. We also find that ground‐based Pc3‐4 waves show a stronger dependence on the solar wind speed than do foreshock ULF waves, suggesting a possible contribution from Kelvin‐Helmholtz instability and shock‐generated transients. Our results provide new insights into the connection between foreshock ULF waves and ground‐based Pc3‐4 waves.
@article{10_1029_2025ja033760, title = {Statistical Relationship Between Foreshock ULF Wave Power and Ground‐Based Pc3‐4 Wave Power}, author = {Liu, T. Z. and Angelopoulos, V. and Dorfman, S. and Hartinger, M. D. and Zhang, K. and Raptis, S. and Ma, D.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA033760}, url = {https://doi.org/10.1029/2025ja033760}, }
APA

Liu, T. Z., Angelopoulos, V., Dorfman, S., Hartinger, M. D., Zhang, K., Raptis, S., Ma, D.(2025). Statistical Relationship Between Foreshock ULF Wave Power and Ground‐Based Pc3‐4 Wave Power. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA033760

BibTeX
```
@article{10_1029_2025ja033760,
  title = {Statistical Relationship Between Foreshock ULF Wave Power and Ground‐Based Pc3‐4 Wave Power},
  author = {Liu, T. Z. and Angelopoulos, V. and Dorfman, S. and Hartinger, M. D. and Zhang, K. and Raptis, S. and Ma, D.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA033760},
  url = {https://doi.org/10.1029/2025ja033760},
}
```
Fermi Acceleration of Electrons at Earth’s Bow Shock Due To Current Sheet Interaction

M. Lindberg, X. Shi, H. Hietala, L. Vuorinen, S. Raptis, F. Koller, and A. Lalti

Journal of Geophysical Research: Space Physics, Mar 2025

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We use the Magnetospheric Multiscale (MMS) mission to present a case study of electron acceleration at Earth’s bow shock due to an interaction with a solar wind magnetic depression. The magnetic depression is identified as a reconnecting current sheet and is observed both at the bow shock, using MMS, and upstream of the shock at the Lagrange point 1 using the ACE, WIND, and DSCOVR spacecraft. The interaction with the current sheet and drop in magnetic field magnitude enables electrons to be accelerated from thermal energies (10–20 eV) up to suprathermal energies (1–5 keV) in a process producing a power‐law with a spectral index close to that predicted by first order Fermi acceleration . The observations are compared to a numerical model of Fermi acceleration considering two approaching magnetic mirrors and pitch angle scattering by whistler waves, and good agreement is shown. Thus, we add another piece to resolving the long‐standing electron injection problem.
@article{10_1029_2025ja034314, title = {Fermi Acceleration of Electrons at Earth's Bow Shock Due To Current Sheet Interaction}, author = {Lindberg, M. and Shi, X. and Hietala, H. and Vuorinen, L. and Raptis, S. and Koller, F. and Lalti, A.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA034314}, url = {https://doi.org/10.1029/2025ja034314}, }
APA

Lindberg, M., Shi, X., Hietala, H., Vuorinen, L., Raptis, S., Koller, F., Lalti, A.(2025). Fermi Acceleration of Electrons at Earth’s Bow Shock Due To Current Sheet Interaction. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA034314

BibTeX
```
@article{10_1029_2025ja034314,
  title = {Fermi Acceleration of Electrons at Earth's Bow Shock Due To Current Sheet Interaction},
  author = {Lindberg, M. and Shi, X. and Hietala, H. and Vuorinen, L. and Raptis, S. and Koller, F. and Lalti, A.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA034314},
  url = {https://doi.org/10.1029/2025ja034314},
}
```
Role of ULF Waves in Reforming the Martian Bow Shock

C. Zhang, C. Dong, T.Z. Liu, C. Mazelle, S. Raptis, H. Zhou, J. Fruchtman, J. Halekas, J. Li, K.G. Hanley, and 3 more authors

AGU Advances, Mar 2025

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Understanding the nature of planetary bow shocks is beneficial for advancing our knowledge of solar wind interactions with planets and fundamental plasma physics processes. Here, we utilize data from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to investigate the Martian bow shock, revealing its distinctive characteristics within our solar system. We find that unlike other planetary shocks, the reformation of Mars’s bow shock driven by the ultra‐low frequency (ULF) waves is more global and less dependent on shock geometries. This distinct behavior is attributed to the broad distribution of ULF waves in the upstream region at Mars, generated not only by shock‐reflected ions but also by planetary protons. Additionally, during the reformation process, the amplitude of the ULF waves and the steepened structures are significantly large. This results in the newly reformed shock exceeding the original one, a phenomenon not observed at other planets under similar shock conditions. Therefore, the ULF waves significantly enhance the complexity of shock dynamics and play a more substantial role at Mars compared to other planets.
@article{10_1029_2025av001654, title = {Role of ULF Waves in Reforming the Martian Bow Shock}, author = {Zhang, C. and Dong, C. and Liu, T. Z. and Mazelle, C. and Raptis, S. and Zhou, H. and Fruchtman, J. and Halekas, J. and Li, J. and Hanley, K. G. and Curry, S. M. and Mitchell, D. L. and Li, X.}, journal = {AGU Advances}, year = {2025}, doi = {10.1029/2025AV001654}, url = {https://doi.org/10.1029/2025av001654}, }
APA

Zhang, C., Dong, C., Liu, T. Z., Mazelle, C., Raptis, S., Zhou, H., Fruchtman, J., Halekas, J., Li, J., Hanley, K. G., Curry, S. M., Mitchell, D. L., Li, X.(2025). Role of ULF Waves in Reforming the Martian Bow Shock. AGU Advances. https://doi.org/10.1029/2025AV001654

BibTeX
```
@article{10_1029_2025av001654,
  title = {Role of ULF Waves in Reforming the Martian Bow Shock},
  author = {Zhang, C. and Dong, C. and Liu, T. Z. and Mazelle, C. and Raptis, S. and Zhou, H. and Fruchtman, J. and Halekas, J. and Li, J. and Hanley, K. G. and Curry, S. M. and Mitchell, D. L. and Li, X.},
  journal = {AGU Advances},
  year = {2025},
  doi = {10.1029/2025AV001654},
  url = {https://doi.org/10.1029/2025av001654},
}
```
Automated classification of MESSENGER plasma observations via unsupervised transfer learning

V. Toy-Edens, W. Mo, R.C. Allen, S.K. Vines, and S. Raptis

Frontiers in Astronomy and Space Sciences, Mar 2025

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Our methodology demonstrates a proof of concept of the applicability of transfer learning for heliophysics, a machine learning technique where knowledge learned from one task is reused to perform a similar unsupervised learning task with additional fine tuning. We applied an unsupervised clustering algorithm, initially trained on data from the Magnetospheric Multiscale (MMS) mission at Earth, to MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) observationsat Mercury to identify three distinct plasma regions: magnetosphere, magnetosheath, and solar wind. While our method requires modifications to the model from post-cleaning rules due to instrument effects, it allows for rapid classification using just a few examples to generate post-cleaning rules. Since there is no ground truth or standardized validation set to compare with, we compare our model’s result with published magnetopause and bow shock lists and find that the clustering algorithm is agreement with 67% of bow shock crossings and 74% of magnetopause crossings. These findings highlight the potential use of clustering algorithms across multiple planetary environments.
@article{10_3389_fspas_2025_1608091, title = {Automated classification of MESSENGER plasma observations via unsupervised transfer learning}, author = {Toy-Edens, V. and Mo, W. and Allen, R. C. and Vines, S. K. and Raptis, S.}, journal = {Frontiers in Astronomy and Space Sciences}, year = {2025}, doi = {10.3389/fspas.2025.1608091}, url = {https://doi.org/10.3389/fspas.2025.1608091}, }
APA

Toy-Edens, V., Mo, W., Allen, R. C., Vines, S. K., Raptis, S.(2025). Automated classification of MESSENGER plasma observations via unsupervised transfer learning. Frontiers in Astronomy and Space Sciences. https://doi.org/10.3389/fspas.2025.1608091

BibTeX
```
@article{10_3389_fspas_2025_1608091,
  title = {Automated classification of MESSENGER plasma observations via unsupervised transfer learning},
  author = {Toy-Edens, V. and Mo, W. and Allen, R. C. and Vines, S. K. and Raptis, S.},
  journal = {Frontiers in Astronomy and Space Sciences},
  year = {2025},
  doi = {10.3389/fspas.2025.1608091},
  url = {https://doi.org/10.3389/fspas.2025.1608091},
}
```

Adaptive PCA-Based Outlier Detection for Multi-feature Time Series in Space Missions

J. Ekelund, S. Raptis, V. Toy-Edens, W. Mo, D.L. Turner, I.J. Cohen, and S. Markidis

In Lecture Notes in Computer Science, Mar 2025

@inproceedings{10_1007_978_3_031_97626_1_18,
  title = {Adaptive PCA-Based Outlier Detection for Multi-feature Time Series in Space Missions},
  author = {Ekelund, J. and Raptis, S. and Toy-Edens, V. and Mo, W. and Turner, D. L. and Cohen, I. J. and Markidis, S.},
  booktitle = {Lecture Notes in Computer Science},
  year = {2025},
  doi = {10.1007/978-3-031-97626-1_18},
  url = {https://doi.org/10.1007/978-3-031-97626-1_18},
}

APA

Ekelund, J., Raptis, S., Toy-Edens, V., Mo, W., Turner, D. L., Cohen, I. J., Markidis, S.(2025). Adaptive PCA-Based Outlier Detection for Multi-feature Time Series in Space Missions. Lecture Notes in Computer Science. https://doi.org/10.1007/978-3-031-97626-1_18

BibTeX

@inproceedings{10_1007_978_3_031_97626_1_18,
  title = {Adaptive PCA-Based Outlier Detection for Multi-feature Time Series in Space Missions},
  author = {Ekelund, J. and Raptis, S. and Toy-Edens, V. and Mo, W. and Turner, D. L. and Cohen, I. J. and Markidis, S.},
  booktitle = {Lecture Notes in Computer Science},
  year = {2025},
  doi = {10.1007/978-3-031-97626-1_18},
  url = {https://doi.org/10.1007/978-3-031-97626-1_18},
}

Interplay Between a Foreshock Bubble and a Hot Flow Anomaly Forming Along the Same Rotational Discontinuity

L. Turc, M.O. Archer, H. Zhou, Y. Pfau‐Kempf, J. Suni, P. Kajdič, X. Blanco‐Cano, S. Dahani, M. Battarbee, S. Raptis, and 8 more authors

Geophysical Research Letters, Mar 2025

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Solar wind directional discontinuities can generate transient mesoscale structures such as foreshock bubbles and hot flow anomalies (HFAs) upstream of Earth’s bow shock. These structures can have a global impact on near‐Earth space, so understanding their formation conditions is essential. We investigate foreshock transient generation at a rotational discontinuity using a global 2D hybrid‐Vlasov simulation. As expected, a foreshock bubble forms on the sunward side of the discontinuity. Later, when the discontinuity reaches the shock, new structures identified as HFAs develop, despite the initial discontinuity not being favorable to HFA formation. We demonstrate that the foreshock bubble provides the necessary conditions for their generation. We then investigate the evolution of the transient structures and the large‐scale bow shock deformation they induce. Our results provide new insights on the formation and evolution of foreshock transients and their impact on the shock.
@article{10_1029_2025gl116473, title = {Interplay Between a Foreshock Bubble and a Hot Flow Anomaly Forming Along the Same Rotational Discontinuity}, author = {Turc, L. and Archer, M. O. and Zhou, H. and Pfau‐Kempf, Y. and Suni, J. and Kajdič, P. and Blanco‐Cano, X. and Dahani, S. and Battarbee, M. and Raptis, S. and Liu, T. Z. and Zhang, H. and Escoubet, C. P. and LaMoury, A. T. and Tao, S. and Lipsanen, V. and Hao, Y. and Palmroth, M.}, journal = {Geophysical Research Letters}, year = {2025}, doi = {10.1029/2025GL116473}, url = {https://doi.org/10.1029/2025gl116473}, }
APA

Turc, L., Archer, M. O., Zhou, H., Pfau‐Kempf, Y., Suni, J., Kajdič, P., Blanco‐Cano, X., Dahani, S., Battarbee, M., Raptis, S., Liu, T. Z., Zhang, H., Escoubet, C. P., LaMoury, A. T., Tao, S., Lipsanen, V., Hao, Y., Palmroth, M.(2025). Interplay Between a Foreshock Bubble and a Hot Flow Anomaly Forming Along the Same Rotational Discontinuity. Geophysical Research Letters. https://doi.org/10.1029/2025GL116473

BibTeX
```
@article{10_1029_2025gl116473,
  title = {Interplay Between a Foreshock Bubble and a Hot Flow Anomaly Forming Along the Same Rotational Discontinuity},
  author = {Turc, L. and Archer, M. O. and Zhou, H. and Pfau‐Kempf, Y. and Suni, J. and Kajdič, P. and Blanco‐Cano, X. and Dahani, S. and Battarbee, M. and Raptis, S. and Liu, T. Z. and Zhang, H. and Escoubet, C. P. and LaMoury, A. T. and Tao, S. and Lipsanen, V. and Hao, Y. and Palmroth, M.},
  journal = {Geophysical Research Letters},
  year = {2025},
  doi = {10.1029/2025GL116473},
  url = {https://doi.org/10.1029/2025gl116473},
}
```
Control of Solar Wind on Magnetic Field Fluctuations in the Subsolar Magnetosheath

Y. Zou, B.M. Walsh, Y. Chen, H. Zhou, and S. Raptis

Journal of Geophysical Research: Space Physics, Mar 2025

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The magnetosheath modifies the solar wind and IMF before they reach Earth’s magnetosphere, and hence plays a crucial role in regulating the solar wind‐magnetosphere interaction. Although the steady component of the magnetosheath magnetic field has been reasonably well reproduced, the fluctuating component has been less accounted for despite its significant amplitude. This paper empirically determines the mean characteristics of the ultra‐low‐frequency magnetic field fluctuations, and constructs a functional form using solar wind parameters. We use 15 years of THEMIS A data for the magnetosheath, and OMNI for the upstream solar wind conditions. Qualitatively, fluctuations are negatively correlated with the IMF cone angle, and positively with the solar wind speed and dynamic pressure. Some fluctuations are correlated with the IMF strength but not all. The level of fluctuations in the IMF is positively correlated with <0.01 Hz fluctuations in the magnetosheath. A higher Mach number is associated with a larger fraction of compressional versus transverse fluctuations in the magnetosheath. Quantitatively, the correlation between magnetosheath fluctuations and individual solar wind parameters is weak, correlation magnitude being <0.5. However, by performing a multiple linear regression fit of the solar wind parameters to magnetosheath fluctuations, a reasonably good prediction can be achieved with correlation magnitude in the range of 0.5–0.7, except for the parallel magnetosheath fluctuations of 0.01–0.1 Hz. Our results are overall consistent with earlier studies, but our quantitative approach further permits forecast of how much the IMF changes inside the magnetosheath which is beneficial for scientific understanding and space weather forecasts.
@article{10_1029_2025ja033856, title = {Control of Solar Wind on Magnetic Field Fluctuations in the Subsolar Magnetosheath}, author = {Zou, Y. and Walsh, B. M. and Chen, Y. and Zhou, H. and Raptis, S.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA033856}, url = {https://doi.org/10.1029/2025ja033856}, }
APA

Zou, Y., Walsh, B. M., Chen, Y., Zhou, H., Raptis, S.(2025). Control of Solar Wind on Magnetic Field Fluctuations in the Subsolar Magnetosheath. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA033856

BibTeX
```
@article{10_1029_2025ja033856,
  title = {Control of Solar Wind on Magnetic Field Fluctuations in the Subsolar Magnetosheath},
  author = {Zou, Y. and Walsh, B. M. and Chen, Y. and Zhou, H. and Raptis, S.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA033856},
  url = {https://doi.org/10.1029/2025ja033856},
}
```
Ground Magnetic Response to an Extraordinary IMF BY Flip During the May 2024 Storm: Travel Time From the Magnetosheath to Dayside High Latitudes

S. Ohtani, Y. Zou, V.G. Merkin, M. Wiltberger, K.H. Pham, S. Raptis, M. Friel, and J.W. Gjerloev

Journal of Geophysical Research: Space Physics, Mar 2025

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In the present study we investigate the response of the dayside ground magnetic field to the sequence of interplanetary magnetic field (IMF) BY changes during the May 2024 geomagnetic storm. We pay particular attention to its extraordinarily large (>120 nT) and abrupt flip, and use GOES‐18 (G18) magnetic field measurements in the dayside magnetosheath as a time reference. In the dayside auroral zone, the northward magnetic component changed by as much as 4,300 nT from negative to positive indicating that the direction of the auroral electrojet changed from westward to eastward. The overall sequence was consistent with the conventional understanding of the IMF BY driving of zonal ionospheric flows and Hall currents, which is also confirmed by a global simulation conducted for this storm. Surprisingly, however, the time delay from G18 to the ground increased significantly in time. The delay was 2–3 min for a sharp BY reduction ∼30 min prior to the BY flip, but it became as long as 10 min for the zero‐crossing of the BY flip. It is suggested that the prolonged time delay reflected the travel time from G18 to the reconnection site, which sensitively depends on the final velocity at the magnetopause, that is, the inflow velocity of the magnetic reconnection. Around the BY flip, the solar wind number density transiently exceeded 100 cm−3, and should have increased further through the bow shock crossing. It is suggested that this unusually dense plasma reduced the reconnection rate, and therefore, the solar wind‐magnetosphere energy coupling due to the extraordinary IMF.
@article{10_1029_2024ja033691, title = {Ground Magnetic Response to an Extraordinary IMF BY Flip During the May 2024 Storm: Travel Time From the Magnetosheath to Dayside High Latitudes}, author = {Ohtani, S. and Zou, Y. and Merkin, V. G. and Wiltberger, M. and Pham, K. H. and Raptis, S. and Friel, M. and Gjerloev, J. W.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2024JA033691}, url = {https://doi.org/10.1029/2024ja033691}, }
APA

Ohtani, S., Zou, Y., Merkin, V. G., Wiltberger, M., Pham, K. H., Raptis, S., Friel, M., Gjerloev, J. W.(2025). Ground Magnetic Response to an Extraordinary IMF BY Flip During the May 2024 Storm: Travel Time From the Magnetosheath to Dayside High Latitudes. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2024JA033691

BibTeX
```
@article{10_1029_2024ja033691,
  title = {Ground Magnetic Response to an Extraordinary IMF BY Flip During the May 2024 Storm: Travel Time From the Magnetosheath to Dayside High Latitudes},
  author = {Ohtani, S. and Zou, Y. and Merkin, V. G. and Wiltberger, M. and Pham, K. H. and Raptis, S. and Friel, M. and Gjerloev, J. W.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2024JA033691},
  url = {https://doi.org/10.1029/2024ja033691},
}
```
Sunward flows in the magnetosheath associated with the magnetic pressure gradient and magnetosheath expansion

H. Madanian, Y. Pfau-Kempf, R. Rice, T. Liu, T. Karlsson, S. Raptis, D. Turner, and J. Beedle

Frontiers in Astronomy and Space Sciences, Mar 2025

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A density structure within the magnetic cloud of an interplanetary coronal mass ejection impacted Earth and caused significant perturbations in plasma boundaries. Using spacecraft data, we describe the effects of this structure on the magnetosheath plasma downstream of the bow shock. During this event, the bow shock breathing motion is evident due to changes in the upstream dynamic pressure. A magnetic enhancement forms in the inner magnetosheath and ahead of a plasma compression region. The structure exhibits characteristics of a fast magnetosonic shock wave, propagating earthward and perpendicular to the background magnetic field and further accelerating the already heated magnetosheath plasma. Following these events, a sunward motion of the magnetosheath plasma is observed. Ion distributions show that both the high-density core population and the high-energy tail of the distribution of the distribution propagate sunward, indicating that the sunward flows are caused by magnetic field line expansion in the very low β magnetosheath plasma. Rarefaction effects and enhancement of the magnetic pressure in the magnetosheath result in magnetic pressure gradient forcing, which drives the expansion of magnetosheath magnetic field lines. This picture is supported by a reasonable agreement between the estimated plasma accelerations and the magnetic pressure gradient force.
@article{10_3389_fspas_2025_1574577, title = {Sunward flows in the magnetosheath associated with the magnetic pressure gradient and magnetosheath expansion}, author = {Madanian, H. and Pfau-Kempf, Y. and Rice, R. and Liu, T. and Karlsson, T. and Raptis, S. and Turner, D. and Beedle, J.}, journal = {Frontiers in Astronomy and Space Sciences}, year = {2025}, doi = {10.3389/fspas.2025.1574577}, url = {https://doi.org/10.3389/fspas.2025.1574577}, }
APA

Madanian, H., Pfau-Kempf, Y., Rice, R., Liu, T., Karlsson, T., Raptis, S., Turner, D., Beedle, J.(2025). Sunward flows in the magnetosheath associated with the magnetic pressure gradient and magnetosheath expansion. Frontiers in Astronomy and Space Sciences. https://doi.org/10.3389/fspas.2025.1574577

BibTeX
```
@article{10_3389_fspas_2025_1574577,
  title = {Sunward flows in the magnetosheath associated with the magnetic pressure gradient and magnetosheath expansion},
  author = {Madanian, H. and Pfau-Kempf, Y. and Rice, R. and Liu, T. and Karlsson, T. and Raptis, S. and Turner, D. and Beedle, J.},
  journal = {Frontiers in Astronomy and Space Sciences},
  year = {2025},
  doi = {10.3389/fspas.2025.1574577},
  url = {https://doi.org/10.3389/fspas.2025.1574577},
}
```
Magnetosheath Jet‐Triggered ULF Waves: Energy Deposition in the Ionosphere

E. Krämer, M. Hamrin, H. Gunell, L. Baddeley, N. Partamies, S. Raptis, K. Herlingshaw, and A. Schillings

Journal of Geophysical Research: Space Physics, Mar 2025

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Magnetosheath jets, transient plasma structures of enhanced dynamic pressure, have been observed to trigger ultra‐low frequency (ULF) waves in the magnetosphere. These ULF waves contribute to energy transport in the magnetosphere‐ionosphere system. Therefore, there is a need to estimate the energy input into the ionosphere due to jet‐triggered ULF waves. In this study, we combine measurements from Magnetospheric Multiscale, ground‐based magnetometers, the EISCAT radar on Svalbard, and SuperDARN to estimate the Joule heating in the ionosphere resulting from jet impacts at the magnetopause. Focusing on three jets observed on 2016‐01‐07 we were able to calculate the Joule heating for two jets. We found an average Joule heating rate of mW/m2 which is on par with other processes such as field line resonances. However, due to the short duration and spatial confinement of the jet‐induced ULF waves, the average energy input was only J. This suggests that the energy deposition of jet‐triggered ULF waves is small compared to other magnetospheric processes, and thus does not significantly impact the average energy budget of the magnetosphere.
@article{10_1029_2025ja033792, title = {Magnetosheath Jet‐Triggered ULF Waves: Energy Deposition in the Ionosphere}, author = {Krämer, E. and Hamrin, M. and Gunell, H. and Baddeley, L. and Partamies, N. and Raptis, S. and Herlingshaw, K. and Schillings, A.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2025}, doi = {10.1029/2025JA033792}, url = {https://doi.org/10.1029/2025ja033792}, }
APA

Krämer, E., Hamrin, M., Gunell, H., Baddeley, L., Partamies, N., Raptis, S., Herlingshaw, K., Schillings, A.(2025). Magnetosheath Jet‐Triggered ULF Waves: Energy Deposition in the Ionosphere. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2025JA033792

BibTeX
```
@article{10_1029_2025ja033792,
  title = {Magnetosheath Jet‐Triggered ULF Waves: Energy Deposition in the Ionosphere},
  author = {Krämer, E. and Hamrin, M. and Gunell, H. and Baddeley, L. and Partamies, N. and Raptis, S. and Herlingshaw, K. and Schillings, A.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2025},
  doi = {10.1029/2025JA033792},
  url = {https://doi.org/10.1029/2025ja033792},
}
```
Multimission Observations of Relativistic Electrons and High-speed Jets Linked to Shock-generated Transients

S. Raptis, M. Lindberg, T.Z. Liu, D.L. Turner, A. Lalti, Y. Zhou, P. Kajdič, A. Kouloumvakos, D.G. Sibeck, L. Vuorinen, and 12 more authors

The Astrophysical Journal Letters, Mar 2025

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MMS highlighted summary

Shock-generated transients, such as hot flow anomalies (HFAs), upstream of planetary bow shocks, play a critical role in electron acceleration. Using multimission data from NASA’s Magnetospheric Multiscale and ESA’s Cluster missions, we demonstrate the transmission of HFAs through Earth’s quasi-parallel bow shock, accelerating electrons to relativistic energies in the process. Energetic electrons initially accelerated upstream are shown to remain broadly confined within the transmitted transient structures downstream, where they get further energized due to the elevated compression levels potentially by betatron acceleration. Additionally, high-speed jets form at the compressive edges of HFAs, exhibiting a significant increase in dynamic pressure and potentially contributing to further localized compression. Our findings emphasize the efficiency of quasi-parallel shocks in driving particle acceleration far beyond the immediate shock transition region, expanding the acceleration region to a larger spatial domain. Finally, this study underscores the importance of a multiscale observational approach in understanding the convoluted processes behind collisionless shock physics and their broader implications.
@article{10_3847_2041_8213_adb154, title = {Multimission Observations of Relativistic Electrons and High-speed Jets Linked to Shock-generated Transients}, author = {Raptis, S. and Lindberg, M. and Liu, T. Z. and Turner, D. L. and Lalti, A. and Zhou, Y. and Kajdič, P. and Kouloumvakos, A. and Sibeck, D. G. and Vuorinen, L. and Michael, A. and Shumko, M. and Osmane, A. and Krämer, E. and Turc, L. and Karlsson, T. and Katsavrias, C. and Wilson, L. B. and Madanian, H. and Blanco-Cano, X. and Cohen, I. J. and Escoubet, C. P.}, journal = {The Astrophysical Journal Letters}, year = {2025}, doi = {10.3847/2041-8213/adb154}, url = {https://doi.org/10.3847/2041-8213/adb154}, }
APA

Raptis, S., Lindberg, M., Liu, T. Z., Turner, D. L., Lalti, A., Zhou, Y., Kajdič, P., Kouloumvakos, A., Sibeck, D. G., Vuorinen, L., Michael, A., Shumko, M., Osmane, A., Krämer, E., Turc, L., Karlsson, T., Katsavrias, C., Wilson, L. B., Madanian, H., Blanco-Cano, X., Cohen, I. J., Escoubet, C. P.(2025). Multimission Observations of Relativistic Electrons and High-speed Jets Linked to Shock-generated Transients. The Astrophysical Journal Letters. https://doi.org/10.3847/2041-8213/adb154

BibTeX
```
@article{10_3847_2041_8213_adb154,
  title = {Multimission Observations of Relativistic Electrons and High-speed Jets Linked to Shock-generated Transients},
  author = {Raptis, S. and Lindberg, M. and Liu, T. Z. and Turner, D. L. and Lalti, A. and Zhou, Y. and Kajdič, P. and Kouloumvakos, A. and Sibeck, D. G. and Vuorinen, L. and Michael, A. and Shumko, M. and Osmane, A. and Krämer, E. and Turc, L. and Karlsson, T. and Katsavrias, C. and Wilson, L. B. and Madanian, H. and Blanco-Cano, X. and Cohen, I. J. and Escoubet, C. P.},
  journal = {The Astrophysical Journal Letters},
  year = {2025},
  doi = {10.3847/2041-8213/adb154},
  url = {https://doi.org/10.3847/2041-8213/adb154},
}
```

Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration

S. Raptis, A. Lalti, M. Lindberg, D.L. Turner, D. Caprioli, and J.L. Burch

Nature Communications, Mar 2025

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MMS highlighted summary ARTEMIS Science Nugget Highlight Press Coverage: Northumbria University Press Coverage: phys.org Press Coverage: sciencedaily.com Behind The Paper: Nature Portfolio

@article{10_1038_s41467_024_55641_9,
  title = {Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration},
  author = {Raptis, S. and Lalti, A. and Lindberg, M. and Turner, D. L. and Caprioli, D. and Burch, J. L.},
  journal = {Nature Communications},
  year = {2025},
  doi = {10.1038/s41467-024-55641-9},
  url = {https://doi.org/10.1038/s41467-024-55641-9},
}

APA

Raptis, S., Lalti, A., Lindberg, M., Turner, D. L., Caprioli, D., Burch, J. L.(2025). Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration. Nature Communications. https://doi.org/10.1038/s41467-024-55641-9

BibTeX

@article{10_1038_s41467_024_55641_9,
  title = {Revealing an unexpectedly low electron injection threshold via reinforced shock acceleration},
  author = {Raptis, S. and Lalti, A. and Lindberg, M. and Turner, D. L. and Caprioli, D. and Burch, J. L.},
  journal = {Nature Communications},
  year = {2025},
  doi = {10.1038/s41467-024-55641-9},
  url = {https://doi.org/10.1038/s41467-024-55641-9},
}

2024

Jets Downstream of Collisionless Shocks: Recent Discoveries and Challenges

E. Krämer, F. Koller, J. Suni, A.T. LaMoury, A. Pöppelwerth, G. Glebe, T. Mohammed-Amin, S. Raptis, L. Vuorinen, S. Weiss, and 12 more authors

Space Science Reviews, Mar 2024

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Plasma flows with enhanced dynamic pressure, known as magnetosheath jets, are often found downstream of collisionless shocks. As they propagate through the magnetosheath, they interact with the surrounding plasma, shaping its properties, and potentially becoming geoeffective upon reaching the magnetopause. In recent years (since 2016), new research has produced vital results that have significantly enhanced our understanding on many aspects of jets. In this review, we summarise and discuss these findings. Spacecraft and ground-based observations, as well as global and local simulations, have contributed greatly to our understanding of the causes and effects of magnetosheath jets. First, we discuss recent findings on jet occurrence and formation, including in other planetary environments. New insights into jet properties and evolution are then examined using observations and simulations. Finally, we review the impact of jets upon interaction with the magnetopause and subsequent consequences for the magnetosphere-ionosphere system. We conclude with an outlook and assessment on future challenges. This includes an overview on future space missions that may prove crucial in tackling the outstanding open questions on jets in the terrestrial magnetosheath as well as other planetary and shock environments.
@article{10_1007_s11214_024_01129_3, title = {Jets Downstream of Collisionless Shocks: Recent Discoveries and Challenges}, author = {Krämer, E. and Koller, F. and Suni, J. and LaMoury, A. T. and Pöppelwerth, A. and Glebe, G. and Mohammed-Amin, T. and Raptis, S. and Vuorinen, L. and Weiss, S. and Xirogiannopoulou, N. and Archer, M. and Blanco-Cano, X. and Gunell, H. and Hietala, H. and Karlsson, T. and Plaschke, F. and Preisser, L. and Roberts, O. and Wedlund, C. Simon and Temmer, M. and Vörös, Z.}, journal = {Space Science Reviews}, year = {2024}, doi = {10.1007/s11214-024-01129-3}, url = {https://doi.org/10.1007/s11214-024-01129-3}, }
APA

Krämer, E., Koller, F., Suni, J., LaMoury, A. T., Pöppelwerth, A., Glebe, G., Mohammed-Amin, T., Raptis, S., Vuorinen, L., Weiss, S., Xirogiannopoulou, N., Archer, M., Blanco-Cano, X., Gunell, H., Hietala, H., Karlsson, T., Plaschke, F., Preisser, L., Roberts, O., Wedlund, C. S., Temmer, M., Vörös, Z.(2024). Jets Downstream of Collisionless Shocks: Recent Discoveries and Challenges. Space Science Reviews. https://doi.org/10.1007/s11214-024-01129-3

BibTeX
```
@article{10_1007_s11214_024_01129_3,
  title = {Jets Downstream of Collisionless Shocks: Recent Discoveries and Challenges},
  author = {Krämer, E. and Koller, F. and Suni, J. and LaMoury, A. T. and Pöppelwerth, A. and Glebe, G. and Mohammed-Amin, T. and Raptis, S. and Vuorinen, L. and Weiss, S. and Xirogiannopoulou, N. and Archer, M. and Blanco-Cano, X. and Gunell, H. and Hietala, H. and Karlsson, T. and Plaschke, F. and Preisser, L. and Roberts, O. and Wedlund, C. Simon and Temmer, M. and Vörös, Z.},
  journal = {Space Science Reviews},
  year = {2024},
  doi = {10.1007/s11214-024-01129-3},
  url = {https://doi.org/10.1007/s11214-024-01129-3},
}
```
On the Formation of Super-Alfvénic Flows Downstream of Collisionless Shocks

A. Osmane and S. Raptis

The Astrophysical Journal, Mar 2024

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Super-Alfvénic jets, with kinetic energy densities significantly exceeding that of the solar wind, are commonly generated downstream of Earth’s bow shock under both high- and low-beta plasma conditions. In this study, we present theoretical evidence that these enhanced kinetic energy flows can be driven by firehose-unstable fluctuations and compressive heating within collisionless plasma environments. Using a fluid formalism that incorporates pressure anisotropy, we estimate that the downstream flow of a collisionless plasma shock can be accelerated by a factor of 2–4 following the compression and saturation of firehose instability. By analyzing quasi-parallel magnetosheath jets observed in situ by the Magnetospheric Multiscale (MMS) mission, we find that approximately 11% of plasma measurements within these jets exhibit firehose-unstable fluctuations. Our findings offer an explanation for the distinctive generation of fast downstream flows in both low (β < 1) and high (β > 1) beta plasmas, and provide new evidence that kinetic processes are crucial for accurately describing the formation and evolution of magnetosheath jets.
@article{10_3847_1538_4357_ad8570, title = {On the Formation of Super-Alfvénic Flows Downstream of Collisionless Shocks}, author = {Osmane, A. and Raptis, S.}, journal = {The Astrophysical Journal}, year = {2024}, doi = {10.3847/1538-4357/ad8570}, url = {https://doi.org/10.3847/1538-4357/ad8570}, }
APA

Osmane, A., Raptis, S.(2024). On the Formation of Super-Alfvénic Flows Downstream of Collisionless Shocks. The Astrophysical Journal. https://doi.org/10.3847/1538-4357/ad8570

BibTeX
```
@article{10_3847_1538_4357_ad8570,
  title = {On the Formation of Super-Alfvénic Flows Downstream of Collisionless Shocks},
  author = {Osmane, A. and Raptis, S.},
  journal = {The Astrophysical Journal},
  year = {2024},
  doi = {10.3847/1538-4357/ad8570},
  url = {https://doi.org/10.3847/1538-4357/ad8570},
}
```
Plasma Sheet Magnetic Flux Transport During Geomagnetic Storms

S. Raptis, V. Merkin, S. Ohtani, M. Gkioulidou, and L.H. Regoli

Geophysical Research Letters, Mar 2024

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MMS highlighted summary

Plasma sheet convection is a key element of storm‐time plasma dynamics in the magnetosphere. While decades of observations have advanced our understanding of convection in general, specifically storm‐time convection remains poorly understood. Using data from ISAS/NASA’s Geotail and NASA’s MMS, this study characterizes plasma sheet magnetic flux transport across the magnetotail during numerous storms (both recovery and main phases) and contrasts these observations with those from quiet times. Our findings confirm the well‐documented enhancement of the convection electric field during geomagnetic storms. Beyond that, our results reveal a significant dawn‐dusk asymmetry. At dawn, the elevated convection is realized via relatively faster flows while at dusk, through a stronger northward magnetic field. These findings suggest a complex feedback loop between plasma sheet convection and ring current buildup, whereby the latter asymmetrically inflates the magnetotail on the dusk side, shifting the reconnection site and subsequently enhanced earthward flows toward dawn.
@article{10_1029_2024gl110839, title = {Plasma Sheet Magnetic Flux Transport During Geomagnetic Storms}, author = {Raptis, S. and Merkin, V. and Ohtani, S. and Gkioulidou, M. and Regoli, L. H.}, journal = {Geophysical Research Letters}, year = {2024}, doi = {10.1029/2024GL110839}, url = {https://doi.org/10.1029/2024gl110839}, }
APA

Raptis, S., Merkin, V., Ohtani, S., Gkioulidou, M., Regoli, L. H.(2024). Plasma Sheet Magnetic Flux Transport During Geomagnetic Storms. Geophysical Research Letters. https://doi.org/10.1029/2024GL110839

BibTeX
```
@article{10_1029_2024gl110839,
  title = {Plasma Sheet Magnetic Flux Transport During Geomagnetic Storms},
  author = {Raptis, S. and Merkin, V. and Ohtani, S. and Gkioulidou, M. and Regoli, L. H.},
  journal = {Geophysical Research Letters},
  year = {2024},
  doi = {10.1029/2024GL110839},
  url = {https://doi.org/10.1029/2024gl110839},
}
```
Transient upstream mesoscale structures: drivers of solar-quiet space weather

P. Kajdič, X. Blanco-Cano, L. Turc, M. Archer, S. Raptis, T.Z. Liu, Y. Pfau-Kempf, A.T. LaMoury, Y. Hao, P.C. Escoubet, and 5 more authors

Frontiers in Astronomy and Space Sciences, Mar 2024

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In recent years, it has become increasingly clear that space weather disturbances can be triggered by transient upstream mesoscale structures (TUMS), independently of the occurrence of large-scale solar wind (SW) structures, such as interplanetary coronal mass ejections and stream interaction regions. Different types of magnetospheric pulsations, transient perturbations of the geomagnetic field and auroral structures are often observed during times when SW monitors indicate quiet conditions, and have been found to be associated to TUMS. In this mini-review we describe the space weather phenomena that have been associated with four of the largest-scale and the most energetic TUMS, namely, hot flow anomalies, foreshock bubbles, travelling foreshocks and foreshock compressional boundaries. The space weather phenomena associated with TUMS tend to be more localized and less intense compared to geomagnetic storms. However, the quiet time space weather may occur more often since, especially during solar minima, quiet SW periods prevail over the perturbed times.
@article{10_3389_fspas_2024_1436916, title = {Transient upstream mesoscale structures: drivers of solar-quiet space weather}, author = {Kajdič, P. and Blanco-Cano, X. and Turc, L. and Archer, M. and Raptis, S. and Liu, T. Z. and Pfau-Kempf, Y. and LaMoury, A. T. and Hao, Y. and Escoubet, P. C. and Omidi, N. and Sibeck, D. G. and Wang, B. and Zhang, H. and Lin, Y.}, journal = {Frontiers in Astronomy and Space Sciences}, year = {2024}, doi = {10.3389/fspas.2024.1436916}, url = {https://doi.org/10.3389/fspas.2024.1436916}, }
APA

Kajdič, P., Blanco-Cano, X., Turc, L., Archer, M., Raptis, S., Liu, T. Z., Pfau-Kempf, Y., LaMoury, A. T., Hao, Y., Escoubet, P. C., Omidi, N., Sibeck, D. G., Wang, B., Zhang, H., Lin, Y.(2024). Transient upstream mesoscale structures: drivers of solar-quiet space weather. Frontiers in Astronomy and Space Sciences. https://doi.org/10.3389/fspas.2024.1436916

BibTeX
```
@article{10_3389_fspas_2024_1436916,
  title = {Transient upstream mesoscale structures: drivers of solar-quiet space weather},
  author = {Kajdič, P. and Blanco-Cano, X. and Turc, L. and Archer, M. and Raptis, S. and Liu, T. Z. and Pfau-Kempf, Y. and LaMoury, A. T. and Hao, Y. and Escoubet, P. C. and Omidi, N. and Sibeck, D. G. and Wang, B. and Zhang, H. and Lin, Y.},
  journal = {Frontiers in Astronomy and Space Sciences},
  year = {2024},
  doi = {10.3389/fspas.2024.1436916},
  url = {https://doi.org/10.3389/fspas.2024.1436916},
}
```
Classifying 8 Years of MMS Dayside Plasma Regions via Unsupervised Machine Learning

V. Toy‐Edens, W. Mo, S. Raptis, and D.L. Turner

Journal of Geophysical Research: Space Physics, Mar 2024

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The Magnetospheric Multiscale (MMS) mission has probed Earth’s magnetosphere, magnetosheath, and near‐Earth solar wind for over 8 years. We utilize an unsupervised learning algorithm, Gaussian mixture model clustering, along with feature generation and simple post‐cleaning methods to automatically classify 8 years of MMS dayside observations into four plasma regions (magnetosphere, magnetosheath, solar wind, and ion foreshock) at 1‐min resolution. With these plasma regions distinguished, we have also identified boundary surfaces (e.g., magnetopause, bow shock). We validate our results on manually generated and rule based region labels described in the literature. We report overlap rates in our cluster determined magnetopauses and bow shocks against Scientist‐in‐the Loop (SITL) identified transitions and published databases. Our features are general and our model is extensible, potentially making it applicable to observational data from multiple other missions.
@article{10_1029_2024ja032431, title = {Classifying 8 Years of MMS Dayside Plasma Regions via Unsupervised Machine Learning}, author = {Toy‐Edens, V. and Mo, W. and Raptis, S. and Turner, D. L.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2024}, doi = {10.1029/2024JA032431}, url = {https://doi.org/10.1029/2024ja032431}, }
APA

Toy‐Edens, V., Mo, W., Raptis, S., Turner, D. L.(2024). Classifying 8 Years of MMS Dayside Plasma Regions via Unsupervised Machine Learning. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2024JA032431

BibTeX
```
@article{10_1029_2024ja032431,
  title = {Classifying 8 Years of MMS Dayside Plasma Regions via Unsupervised Machine Learning},
  author = {Toy‐Edens, V. and Mo, W. and Raptis, S. and Turner, D. L.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2024},
  doi = {10.1029/2024JA032431},
  url = {https://doi.org/10.1029/2024ja032431},
}
```
Temporal Evolution of O+ Population in the Near‐Earth Plasma Sheet During Geomagnetic Storms as Observed by the Magnetospheric Multiscale Mission

L.H. Regoli, M. Gkioulidou, S. Ohtani, S. Raptis, C.G. Mouikis, L.M. Kistler, I.J. Cohen, and S.A. Fuselier

Journal of Geophysical Research: Space Physics, Mar 2024

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During geomagnetic storms, the increase in energy input into the ionosphere in the form of Poynting flux and electron precipitation leads to an enhanced ionospheric outflow that results in an increase of the O+ content in the magnetosphere. Using different missions and instrumentation, two main ionospheric sources have been identified for the oxygen ions reaching the inner magnetosphere during geomagnetic storms: the dayside cusp, and the night side auroral region. Evidence of both pathways have been presented in the literature. However, the relative contribution of each of these pathways to the enhancement of O+ observed in near‐Earth plasma sheet, as well as the dynamics involved during the development of geomagnetic storms remains an open question. Here, we present the first statistical study to date to address this question, in the form of a superposed epoch analysis of O+ and H+ moments obtained by the Magnetospheric Multiscale (MMS) mission throughout the main phase of 90 geomagnetic storms with a minimum SYM‐H of at least −50 nT. The results show a clear increase in the oxygen density in the near‐Earth plasma sheet, with values further from Earth remaining low. Temperature values for both species show an increase with the progress of the storms. These results combined suggest that, during the main phase of geomagnetic storms, most of the oxygen ions observed in the near‐Earth plasma sheet are traveling directly from the nightside auroral region.
@article{10_1029_2023ja032203, title = {Temporal Evolution of O+ Population in the Near‐Earth Plasma Sheet During Geomagnetic Storms as Observed by the Magnetospheric Multiscale Mission}, author = {Regoli, L. H. and Gkioulidou, M. and Ohtani, S. and Raptis, S. and Mouikis, C. G. and Kistler, L. M. and Cohen, I. J. and Fuselier, S. A.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2024}, doi = {10.1029/2023JA032203}, url = {https://doi.org/10.1029/2023ja032203}, }
APA

Regoli, L. H., Gkioulidou, M., Ohtani, S., Raptis, S., Mouikis, C. G., Kistler, L. M., Cohen, I. J., Fuselier, S. A.(2024). Temporal Evolution of O+ Population in the Near‐Earth Plasma Sheet During Geomagnetic Storms as Observed by the Magnetospheric Multiscale Mission. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2023JA032203

BibTeX
```
@article{10_1029_2023ja032203,
  title = {Temporal Evolution of O+ Population in the Near‐Earth Plasma Sheet During Geomagnetic Storms as Observed by the Magnetospheric Multiscale Mission},
  author = {Regoli, L. H. and Gkioulidou, M. and Ohtani, S. and Raptis, S. and Mouikis, C. G. and Kistler, L. M. and Cohen, I. J. and Fuselier, S. A.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2024},
  doi = {10.1029/2023JA032203},
  url = {https://doi.org/10.1029/2023ja032203},
}
```
The Effect of Fast Solar Wind on Ion Distribution Downstream of Earth’s Bow Shock

F. Koller, S. Raptis, M. Temmer, and T. Karlsson

The Astrophysical Journal Letters, Mar 2024

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The solar wind gets thermalized and compressed when crossing a planetary bow shock, forming the magnetosheath. The angle between the upstream magnetic field and the shock normal vector separates the quasi-parallel from the quasi-perpendicular magnetosheath, significantly influencing the physical conditions in these regions. A reliable classification between both magnetosheath regions is of utmost importance since different phenomena and physical processes take place on each. The complexity of this classification is increased due to the origin and variability of the solar wind. Using measurements from the Time History of Events and Macroscale Interactions during Substorms mission and OMNI data between 2008 and 2023, we demonstrate the importance of magnetosheath classification across various solar wind plasma origins. We focus on investigating the ion energy fluxes in the high-energy range for each solar wind type, which typically serves as an indicator for foreshock activity and thus separating the quasi-parallel from quasi-perpendicular magnetosheath. Dividing the data set into different regimes reveals that fast solar wind plasma originating from coronal holes causes exceptionally high-energy ion fluxes even in the quasi-perpendicular environment. This stands in stark contrast to all other solar wind types, highlighting that magnetosheath classification is inherently biased if not all types of solar wind are considered in the classification. Combining knowledge of solar wind origins and structures with shock and magnetosheath research thus contributes to an improved magnetosheath characterization. This is particularly valuable in big-data machine-learning applications within heliophysics, which requires clean and verified data sets for optimal performance.
@article{10_3847_2041_8213_ad2ddf, title = {The Effect of Fast Solar Wind on Ion Distribution Downstream of Earth’s Bow Shock}, author = {Koller, F. and Raptis, S. and Temmer, M. and Karlsson, T.}, journal = {The Astrophysical Journal Letters}, year = {2024}, doi = {10.3847/2041-8213/ad2ddf}, url = {https://doi.org/10.3847/2041-8213/ad2ddf}, }
APA

Koller, F., Raptis, S., Temmer, M., Karlsson, T.(2024). The Effect of Fast Solar Wind on Ion Distribution Downstream of Earth’s Bow Shock. The Astrophysical Journal Letters. https://doi.org/10.3847/2041-8213/ad2ddf

BibTeX
```
@article{10_3847_2041_8213_ad2ddf,
  title = {The Effect of Fast Solar Wind on Ion Distribution Downstream of Earth’s Bow Shock},
  author = {Koller, F. and Raptis, S. and Temmer, M. and Karlsson, T.},
  journal = {The Astrophysical Journal Letters},
  year = {2024},
  doi = {10.3847/2041-8213/ad2ddf},
  url = {https://doi.org/10.3847/2041-8213/ad2ddf},
}
```
Electron Acceleration at Earth’s Bow Shock Due to Stochastic Shock Drift Acceleration

M. Lindberg, A. Vaivads, T. Amano, S. Raptis, and S. Joshi

Geophysical Research Letters, Mar 2024

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We use the Magnetospheric Multiscale mission (MMS) to study electron acceleration at Earth’s quasi‐perpendicular bow shock to address the long‐standing electron injection problem. The observations are compared to the predictions of the stochastic shock drift acceleration (SSDA) theory. Recent studies based on SSDA predict electron distribution being a power law with a cutoff energy that scales with upstream parameters. This scaling law has been successfully tested for a single Earth’s bow shock crossing by MMS. Here we extend this study and test the prediction of the scaling law for seven MMS Earth’s bow shock crossings with different upstream parameters. A goodness‐of‐fit test shows good agreement between observations and SSDA theoretical predictions, thus supporting SSDA as one of the most promising candidates for solving the electron injection problem.
@article{10_1029_2023gl106612, title = {Electron Acceleration at Earth's Bow Shock Due to Stochastic Shock Drift Acceleration}, author = {Lindberg, M. and Vaivads, A. and Amano, T. and Raptis, S. and Joshi, S.}, journal = {Geophysical Research Letters}, year = {2024}, doi = {10.1029/2023GL106612}, url = {https://doi.org/10.1029/2023gl106612}, }
APA

Lindberg, M., Vaivads, A., Amano, T., Raptis, S., Joshi, S.(2024). Electron Acceleration at Earth’s Bow Shock Due to Stochastic Shock Drift Acceleration. Geophysical Research Letters. https://doi.org/10.1029/2023GL106612

BibTeX
```
@article{10_1029_2023gl106612,
  title = {Electron Acceleration at Earth's Bow Shock Due to Stochastic Shock Drift Acceleration},
  author = {Lindberg, M. and Vaivads, A. and Amano, T. and Raptis, S. and Joshi, S.},
  journal = {Geophysical Research Letters},
  year = {2024},
  doi = {10.1029/2023GL106612},
  url = {https://doi.org/10.1029/2023gl106612},
}
```
Magnetosheath jets at Jupiter and across the solar system

Y. Zhou, S. Raptis, S. Wang, C. Shen, N. Ren, and L. Ma

Nature Communications, Mar 2024

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Press Coverage: phys.org Press Coverage: Astronomy Magazine

The study of jets in the Earth’s magnetosheath has been a subject of extensive investigation for over a decade due to their profound impact on the geomagnetic environment and their close connection with shock dynamics. While the variability of the solar wind and its interaction with Earth’s magnetosphere provide valuable insights into jets across a range of parameters, a broader parameter space can be explored by examining the magnetosheath of other planets. Here we report the existence of anti-sunward and sunward jets in the Jovian magnetosheath and show their close association with magnetic discontinuities. The anti-sunward jets are possibly generated by a shock–discontinuity interaction. Finally, through a comparative analysis of jets observed at Earth, Mars, and Jupiter, we show that the size of jets scales with the size of bow shock.
@article{10_1038_s41467_023_43942_4, title = {Magnetosheath jets at Jupiter and across the solar system}, author = {Zhou, Y. and Raptis, S. and Wang, S. and Shen, C. and Ren, N. and Ma, L.}, journal = {Nature Communications}, year = {2024}, doi = {10.1038/s41467-023-43942-4}, url = {https://doi.org/10.1038/s41467-023-43942-4}, }
APA

Zhou, Y., Raptis, S., Wang, S., Shen, C., Ren, N., Ma, L.(2024). Magnetosheath jets at Jupiter and across the solar system. Nature Communications. https://doi.org/10.1038/s41467-023-43942-4

BibTeX
```
@article{10_1038_s41467_023_43942_4,
  title = {Magnetosheath jets at Jupiter and across the solar system},
  author = {Zhou, Y. and Raptis, S. and Wang, S. and Shen, C. and Ren, N. and Ma, L.},
  journal = {Nature Communications},
  year = {2024},
  doi = {10.1038/s41467-023-43942-4},
  url = {https://doi.org/10.1038/s41467-023-43942-4},
}
```

2023

Shocklets and Short Large Amplitude Magnetic Structures (SLAMS) in the High Mach Foreshock of Venus

G.A. Collinson, H. Hietala, F. Plaschke, T. Karlsson, L.B. Wilson, M. Archer, M. Battarbee, X. Blanco‐Cano, C. Bertucci, D. Long, and 9 more authors

Geophysical Research Letters, Mar 2023

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Shocklets and short large‐amplitude magnetic structures (SLAMS) are steepened magnetic fluctuations commonly found in Earth’s upstream foreshock. Here we present Venus Express observations from the 26th of February 2009 establishing their existence in the steady‐state foreshock of Venus, building on a past study which found SLAMS during a substantial disturbance of the induced magnetosphere. The Venusian structures were comparable to those reported near Earth. The 2 Shocklets had magnetic compression ratios of 1.23 and 1.34 with linear polarization in the spacecraft frame. The 3 SLAMS had ratios between 3.22 and 4.03, two of which with elliptical polarization in the spacecraft frame. Statistical analysis suggests SLAMS coincide with unusually high solar wind Alfvén mach‐number at Venus (12.5, this event). Thus, while we establish Shocklets and SLAMS can form in the stable Venusian foreshock, they may be rarer than at Earth. We estimate a lower limit of their occurrence rate of ≳14%.
@article{10_1029_2023gl104610, title = {Shocklets and Short Large Amplitude Magnetic Structures (SLAMS) in the High Mach Foreshock of Venus}, author = {Collinson, G. A. and Hietala, H. and Plaschke, F. and Karlsson, T. and Wilson, L. B. and Archer, M. and Battarbee, M. and Blanco‐Cano, X. and Bertucci, C. and Long, D. and Opher, M. and Sergis, N. and Gasque, C. and Liu, T. and Raptis, S. and Burne, S. and Frahm, R. and Zhang, T. and Futaana, Y.}, journal = {Geophysical Research Letters}, year = {2023}, doi = {10.1029/2023GL104610}, url = {https://doi.org/10.1029/2023gl104610}, }
APA

Collinson, G. A., Hietala, H., Plaschke, F., Karlsson, T., Wilson, L. B., Archer, M., Battarbee, M., Blanco‐Cano, X., Bertucci, C., Long, D., Opher, M., Sergis, N., Gasque, C., Liu, T., Raptis, S., Burne, S., Frahm, R., Zhang, T., Futaana, Y.(2023). Shocklets and Short Large Amplitude Magnetic Structures (SLAMS) in the High Mach Foreshock of Venus. Geophysical Research Letters. https://doi.org/10.1029/2023GL104610

BibTeX
```
@article{10_1029_2023gl104610,
  title = {Shocklets and Short Large Amplitude Magnetic Structures (SLAMS) in the High Mach Foreshock of Venus},
  author = {Collinson, G. A. and Hietala, H. and Plaschke, F. and Karlsson, T. and Wilson, L. B. and Archer, M. and Battarbee, M. and Blanco‐Cano, X. and Bertucci, C. and Long, D. and Opher, M. and Sergis, N. and Gasque, C. and Liu, T. and Raptis, S. and Burne, S. and Frahm, R. and Zhang, T. and Futaana, Y.},
  journal = {Geophysical Research Letters},
  year = {2023},
  doi = {10.1029/2023GL104610},
  url = {https://doi.org/10.1029/2023gl104610},
}
```
Velocity of magnetic holes in the solar wind from Cluster multipoint measurements

H. Trollvik, T. Karlsson, and S. Raptis

Annales Geophysicae, Mar 2023

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. We present the first statistical study on the velocity of magnetic holes (MHs) in the solar wind. Magnetic holes are localized depressions of the magnetic field, often divided into two classes: rotational and linear MHs. We have conducted a timing analysis of observations of MHs from the Cluster mission in the first quarter of 2005. In total, 69 events were used; out of these, there were 40 linear and 29 rotational MHs, where the limit of magnetic field rotation was set to 50∘. The resulting median velocity was 7.4 ± 45 and 25 ± 42 km s−1 for linear and rotational MHs, respectively. For both classes, around 70 % of the events had a velocity in the solar wind frame that was lower than the Alfvén velocity. Therefore, we conclude that within the observational uncertainties, both linear and rotational MHs are convected with the solar wind.
@article{10_5194_angeo_41_327_2023, title = {Velocity of magnetic holes in the solar wind from Cluster multipoint measurements}, author = {Trollvik, H. and Karlsson, T. and Raptis, S.}, journal = {Annales Geophysicae}, year = {2023}, doi = {10.5194/angeo-41-327-2023}, url = {https://doi.org/10.5194/angeo-41-327-2023}, }
APA

Trollvik, H., Karlsson, T., Raptis, S.(2023). Velocity of magnetic holes in the solar wind from Cluster multipoint measurements. Annales Geophysicae. https://doi.org/10.5194/angeo-41-327-2023

BibTeX
```
@article{10_5194_angeo_41_327_2023,
  title = {Velocity of magnetic holes in the solar wind from Cluster multipoint measurements},
  author = {Trollvik, H. and Karlsson, T. and Raptis, S.},
  journal = {Annales Geophysicae},
  year = {2023},
  doi = {10.5194/angeo-41-327-2023},
  url = {https://doi.org/10.5194/angeo-41-327-2023},
}
```
MMS Observation of Two‐Step Electron Acceleration at Earth’s Bow Shock

M. Lindberg, A. Vaivads, S. Raptis, and T. Karlsson

Geophysical Research Letters, Mar 2023

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We use the Magnetospheric Multiscale mission to observe a bi‐directional electron acceleration event in the electron foreshock upstream of Earth’s quasi‐perpendicular collisionless bow shock. The acceleration region is associated with a decrease in wave activity, inconsistent with common electron acceleration mechanisms such as Diffusive Shock Acceleration and Stochastic Shock Drift Acceleration. We propose a two‐step acceleration process where an electron field‐aligned beam acts as a seed population further accelerated by a shrinking magnetic bottle process, with the shock acting as the magnetic mirror(s).
@article{10_1029_2023gl104714, title = {MMS Observation of Two‐Step Electron Acceleration at Earth's Bow Shock}, author = {Lindberg, M. and Vaivads, A. and Raptis, S. and Karlsson, T.}, journal = {Geophysical Research Letters}, year = {2023}, doi = {10.1029/2023GL104714}, url = {https://doi.org/10.1029/2023gl104714}, }
APA

Lindberg, M., Vaivads, A., Raptis, S., Karlsson, T.(2023). MMS Observation of Two‐Step Electron Acceleration at Earth’s Bow Shock. Geophysical Research Letters. https://doi.org/10.1029/2023GL104714

BibTeX
```
@article{10_1029_2023gl104714,
  title = {MMS Observation of Two‐Step Electron Acceleration at Earth's Bow Shock},
  author = {Lindberg, M. and Vaivads, A. and Raptis, S. and Karlsson, T.},
  journal = {Geophysical Research Letters},
  year = {2023},
  doi = {10.1029/2023GL104714},
  url = {https://doi.org/10.1029/2023gl104714},
}
```

2022

Solar wind magnetic holes can cross the bow shock and enter the magnetosheath

T. Karlsson, H. Trollvik, S. Raptis, H. Nilsson, and H. Madanian

Annales Geophysicae, Mar 2022

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. Solar wind magnetic holes are localized depressions of the magnetic field strength, on timescales of seconds to minutes. We use Cluster multipoint measurements to identify 26 magnetic holes which are observed just upstream of the bow shock and, a short time later, downstream in the magnetosheath, thus showing that they can penetrate the bow shock and enter the magnetosheath. For two magnetic holes, we show that the relation between upstream and downstream properties of the magnetic holes are well described by the MHD (magnetohydrodynamic) Rankine–Hugoniot (RH) jump conditions. We also present a small statistical investigation of the correlation between upstream and downstream observations of some properties of the magnetic holes. The temporal scale size and magnetic field rotation across the magnetic holes are very similar for the upstream and downstream observations, while the depth of the magnetic holes varies more. The results are consistent with the interpretation that magnetic holes in Earth’s and Mercury’s magnetosheath are of solar wind origin, as has previously been suggested. Since the solar wind magnetic holes can enter the magnetosheath, they may also interact with the magnetopause, representing a new type of localized solar wind–magnetosphere interaction.
@article{10_5194_angeo_40_687_2022, title = {Solar wind magnetic holes can cross the bow shock and enter the magnetosheath}, author = {Karlsson, T. and Trollvik, H. and Raptis, S. and Nilsson, H. and Madanian, H.}, journal = {Annales Geophysicae}, year = {2022}, doi = {10.5194/angeo-40-687-2022}, url = {https://doi.org/10.5194/angeo-40-687-2022}, }
APA

Karlsson, T., Trollvik, H., Raptis, S., Nilsson, H., Madanian, H.(2022). Solar wind magnetic holes can cross the bow shock and enter the magnetosheath. Annales Geophysicae. https://doi.org/10.5194/angeo-40-687-2022

BibTeX
```
@article{10_5194_angeo_40_687_2022,
  title = {Solar wind magnetic holes can cross the bow shock and enter the magnetosheath},
  author = {Karlsson, T. and Trollvik, H. and Raptis, S. and Nilsson, H. and Madanian, H.},
  journal = {Annales Geophysicae},
  year = {2022},
  doi = {10.5194/angeo-40-687-2022},
  url = {https://doi.org/10.5194/angeo-40-687-2022},
}
```
Dynamics of Earth’s bow shock under near-radial interplanetary magnetic field conditions

C.J. Pollock, L. Chen, S.J. Schwartz, S. Wang, L. Avanov, J.L. Burch, D.J. Gershman, B.L. Giles, S. Raptis, and C.T. Russell

Physics of Plasmas, Mar 2022

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We investigate the dynamics of Earth’s quasi-parallel terrestrial bow shock based on measurements from the Magnetospheric MultiScale (MMS) spacecraft constellation during a period of near-radial interplanetary magnetic conditions, when the interplanetary magnetic field and the solar wind (SW) velocity are nearly anti-parallel. High-speed earthward ion flows with properties that are similar to those of the pristine SW are observed to be embedded within the magnetosheath-like plasma. These flows are accompanied by Interplanetary Magnetic Field (IMF) intensity of less than about 10 nT, compared to nearby magnetosheath intensities of generally greater than 10 nT. The high-speed flow intervals are bounded at their leading and trailing edges by intense fluxes of more energetic ions and large amplitude quasi-sinusoidal magnetic oscillations, similar to ultra-low frequency waves known to steepen and pileup on approach toward Earth to form the quasi-parallel bow shock. The MMS string-of-pearls configuration is aligned with the outbound trajectory and provides inter-spacecraft separations of several hundred km along its near 103 length, allowing sequential observation of the plasma and magnetic field signatures during the event by the four spacecraft. The SW-like interval is most distinct at the outer-most MMS-2 and sequentially less distinct at each of the trailing MMS spacecraft. We discuss the interpretation of this event alternatively as MMS having observed a quasi-rigid bow shock contraction/expansion cycle, ripples or undulations propagating on the bow shock surface, or a more spatially local evolution in the context of either a deeply deformed shock surface or a porous shock surface, as in the three-dimensional patchwork concept of the quasi-parallel bow shock, under the extant near-radial IMF condition.
@article{10_1063_5_0089937, title = {Dynamics of Earth's bow shock under near-radial interplanetary magnetic field conditions}, author = {Pollock, C. J. and Chen, L. and Schwartz, S. J. and Wang, S. and Avanov, L. and Burch, J. L. and Gershman, D. J. and Giles, B. L. and Raptis, S. and Russell, C. T.}, journal = {Physics of Plasmas}, year = {2022}, doi = {10.1063/5.0089937}, url = {https://doi.org/10.1063/5.0089937}, }
APA

Pollock, C. J., Chen, L., Schwartz, S. J., Wang, S., Avanov, L., Burch, J. L., Gershman, D. J., Giles, B. L., Raptis, S., Russell, C. T.(2022). Dynamics of Earth’s bow shock under near-radial interplanetary magnetic field conditions. Physics of Plasmas. https://doi.org/10.1063/5.0089937

BibTeX
```
@article{10_1063_5_0089937,
  title = {Dynamics of Earth's bow shock under near-radial interplanetary magnetic field conditions},
  author = {Pollock, C. J. and Chen, L. and Schwartz, S. J. and Wang, S. and Avanov, L. and Burch, J. L. and Gershman, D. J. and Giles, B. L. and Raptis, S. and Russell, C. T.},
  journal = {Physics of Plasmas},
  year = {2022},
  doi = {10.1063/5.0089937},
  url = {https://doi.org/10.1063/5.0089937},
}
```
On Magnetosheath Jet Kinetic Structure and Plasma Properties

S. Raptis, T. Karlsson, A. Vaivads, M. Lindberg, A. Johlander, and H. Trollvik

Geophysical Research Letters, Mar 2022

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MMS highlighted summary

High‐speed plasma jets downstream of Earth’s bow shock are high velocity streams associated with a variety of shock and magnetospheric phenomena. In this work, using the Magnetosphere Multiscale mission, we study the properties of a jet found downstream of the Quasi‐parallel bow shock using high‐resolution (burst) data. By doing so, we demonstrate how the jet is an inherently kinetic structure described by highly variable velocity distributions. The observed distributions show the presence of two plasma population, a cold/fast jet and a hotter/slower background population. We derive partial moments for the jet population to isolate its properties. The resulting partial moments appear different from the full ones which are typically used in similar studies. These discrepancies show how jets are more similar to upstream solar wind beams compared to what was previously believed. Finally, we explore the consequences of our results and methodology regarding the characterization, origin, and evolution of jets.
@article{10_1029_2022gl100678, title = {On Magnetosheath Jet Kinetic Structure and Plasma Properties}, author = {Raptis, S. and Karlsson, T. and Vaivads, A. and Lindberg, M. and Johlander, A. and Trollvik, H.}, journal = {Geophysical Research Letters}, year = {2022}, doi = {10.1029/2022GL100678}, url = {https://doi.org/10.1029/2022gl100678}, }
APA

Raptis, S., Karlsson, T., Vaivads, A., Lindberg, M., Johlander, A., Trollvik, H.(2022). On Magnetosheath Jet Kinetic Structure and Plasma Properties. Geophysical Research Letters. https://doi.org/10.1029/2022GL100678

BibTeX
```
@article{10_1029_2022gl100678,
  title = {On Magnetosheath Jet Kinetic Structure and Plasma Properties},
  author = {Raptis, S. and Karlsson, T. and Vaivads, A. and Lindberg, M. and Johlander, A. and Trollvik, H.},
  journal = {Geophysical Research Letters},
  year = {2022},
  doi = {10.1029/2022GL100678},
  url = {https://doi.org/10.1029/2022gl100678},
}
```
Electron Kinetic Entropy across Quasi-Perpendicular Shocks

M. Lindberg, A. Vaivads, S. Raptis, P. Lindqvist, B.L. Giles, and D.J. Gershman

Entropy, Mar 2022

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We use Magnetospheric Multiscale (MMS) data to study electron kinetic entropy per particle Se across Earth’s quasi-perpendicular bow shock. We have selected 22 shock crossings covering a wide range of shock conditions. Measured distribution functions are calibrated and corrected for spacecraft potential, secondary electron contamination, lack of measurements at the lowest energies and electron density measurements based on plasma frequency measurements. All crossings display an increase in electron kinetic entropy across the shock ΔSe being positive or zero within their error margin. There is a strong dependence of ΔSe on the change in electron temperature, ΔTe, and the upstream electron plasma beta, βe. Shocks with large ΔTe have large ΔSe. Shocks with smaller βe are associated with larger ΔSe. We use the values of ΔSe, ΔTe and density change Δne to determine the effective adiabatic index of electrons for each shock crossing. The average effective adiabatic index is ⟨γe⟩=1.64±0.07.
@article{10_3390_e24060745, title = {Electron Kinetic Entropy across Quasi-Perpendicular Shocks}, author = {Lindberg, M. and Vaivads, A. and Raptis, S. and Lindqvist, P. and Giles, B. L. and Gershman, D. J.}, journal = {Entropy}, year = {2022}, doi = {10.3390/e24060745}, url = {https://doi.org/10.3390/e24060745}, }
APA

Lindberg, M., Vaivads, A., Raptis, S., Lindqvist, P., Giles, B. L., Gershman, D. J.(2022). Electron Kinetic Entropy across Quasi-Perpendicular Shocks. Entropy. https://doi.org/10.3390/e24060745

BibTeX
```
@article{10_3390_e24060745,
  title = {Electron Kinetic Entropy across Quasi-Perpendicular Shocks},
  author = {Lindberg, M. and Vaivads, A. and Raptis, S. and Lindqvist, P. and Giles, B. L. and Gershman, D. J.},
  journal = {Entropy},
  year = {2022},
  doi = {10.3390/e24060745},
  url = {https://doi.org/10.3390/e24060745},
}
```
Downstream high-speed plasma jet generation as a direct consequence of shock reformation

S. Raptis, T. Karlsson, A. Vaivads, C. Pollock, F. Plaschke, A. Johlander, H. Trollvik, and P. Lindqvist

Nature Communications, Mar 2022

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Editor Highlighted: Focus : Astronomy and planetary science Press Coverage: KTH Press Coverage: phys.org Press Coverage: spacedaily.com Behind The Paper: Nature Portfolio

Springer Nature 2022 Astronomy Highlight

Shocks are one of nature’s most powerful particle accelerators and have been connected to relativistic electron acceleration and cosmic rays. Upstream shock observations include wave generation, wave-particle interactions and magnetic compressive structures, while at the shock and downstream, particle acceleration, magnetic reconnection and plasma jets can be observed. Here, using Magnetospheric Multiscale (MMS) we show in-situ evidence of high-speed downstream flows (jets) generated at the Earth’s bow shock as a direct consequence of shock reformation. Jets are observed downstream due to a combined effect of upstream plasma wave evolution and an ongoing reformation cycle of the bow shock. This generation process can also be applicable to planetary and astrophysical plasmas where collisionless shocks are commonly found.
@article{10_1038_s41467_022_28110_4, title = {Downstream high-speed plasma jet generation as a direct consequence of shock reformation}, author = {Raptis, S. and Karlsson, T. and Vaivads, A. and Pollock, C. and Plaschke, F. and Johlander, A. and Trollvik, H. and Lindqvist, P.}, journal = {Nature Communications}, year = {2022}, doi = {10.1038/s41467-022-28110-4}, url = {https://doi.org/10.1038/s41467-022-28110-4}, }
APA

Raptis, S., Karlsson, T., Vaivads, A., Pollock, C., Plaschke, F., Johlander, A., Trollvik, H., Lindqvist, P.(2022). Downstream high-speed plasma jet generation as a direct consequence of shock reformation. Nature Communications. https://doi.org/10.1038/s41467-022-28110-4

BibTeX
```
@article{10_1038_s41467_022_28110_4,
  title = {Downstream high-speed plasma jet generation as a direct consequence of shock reformation},
  author = {Raptis, S. and Karlsson, T. and Vaivads, A. and Pollock, C. and Plaschke, F. and Johlander, A. and Trollvik, H. and Lindqvist, P.},
  journal = {Nature Communications},
  year = {2022},
  doi = {10.1038/s41467-022-28110-4},
  url = {https://doi.org/10.1038/s41467-022-28110-4},
}
```

2021

Solar Energetic Particle Event occurrence prediction using Solar Flare Soft X-ray measurements and Machine Learning

S. Aminalragia-Giamini, S. Raptis, A. Anastasiadis, A. Tsigkanos, I. Sandberg, A. Papaioannou, C. Papadimitriou, P. Jiggens, A. Aran, and I.A. Daglis

Journal of Space Weather and Space Climate, Mar 2021

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The prediction of the occurrence of Solar Energetic Particle (SEP) events has been investigated over many years, and multiple works have presented significant advances in this problem. The accurate and timely prediction of SEPs is of interest to the scientific community as well as mission designers, operators, and industrial partners due to the threat SEPs pose to satellites, spacecrafts, and crewed missions. In this work, we present a methodology for the prediction of SEPs from the soft X-rays of solar flares associated with SEPs that were measured in 1 AU. We use an expansive dataset covering 25 years of solar activity, 1988–2013, which includes thousands of flares and more than two hundred identified and catalogued SEPs. Neural networks are employed as the predictors in the model, providing probabilities for the occurrence or not of a SEP, which are converted to yes/no predictions. The neural networks are designed using current and state-of-the-art tools integrating recent advances in the machine learning field. The results of the methodology are extensively evaluated and validated using all the available data, and it is shown that we achieve very good levels of accuracy with correct SEP occurrence prediction higher than 85% and correct no-SEP predictions higher than 92%. Finally, we discuss further work towards potential improvements and the applicability of our model in real-life conditions.
@article{10_1051_swsc_2021043, title = {Solar Energetic Particle Event occurrence prediction using Solar Flare Soft X-ray measurements and Machine Learning}, author = {Aminalragia-Giamini, S. and Raptis, S. and Anastasiadis, A. and Tsigkanos, A. and Sandberg, I. and Papaioannou, A. and Papadimitriou, C. and Jiggens, P. and Aran, A. and Daglis, I. A.}, journal = {Journal of Space Weather and Space Climate}, year = {2021}, doi = {10.1051/swsc/2021043}, url = {https://doi.org/10.1051/swsc/2021043}, }
APA

Aminalragia-Giamini, S., Raptis, S., Anastasiadis, A., Tsigkanos, A., Sandberg, I., Papaioannou, A., Papadimitriou, C., Jiggens, P., Aran, A., Daglis, I. A.(2021). Solar Energetic Particle Event occurrence prediction using Solar Flare Soft X-ray measurements and Machine Learning. Journal of Space Weather and Space Climate. https://doi.org/10.1051/swsc/2021043

BibTeX
```
@article{10_1051_swsc_2021043,
  title = {Solar Energetic Particle Event occurrence prediction using Solar Flare Soft X-ray measurements and Machine Learning},
  author = {Aminalragia-Giamini, S. and Raptis, S. and Anastasiadis, A. and Tsigkanos, A. and Sandberg, I. and Papaioannou, A. and Papadimitriou, C. and Jiggens, P. and Aran, A. and Daglis, I. A.},
  journal = {Journal of Space Weather and Space Climate},
  year = {2021},
  doi = {10.1051/swsc/2021043},
  url = {https://doi.org/10.1051/swsc/2021043},
}
```
Classifying the Magnetosheath Behind the Quasi‐Parallel and Quasi‐Perpendicular Bow Shock by Local Measurements

T. Karlsson, S. Raptis, H. Trollvik, and H. Nilsson

Journal of Geophysical Research: Space Physics, Mar 2021

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We investigate and evaluate the possibility of using local magnetosheath measurements to classify the plasma according to upstream conditions. In order to do this, we use simultaneous measurements from the Cluster spacecraft from time intervals when one of them is located in the solar wind, and the other in the magnetosheath. In particular, we study the classification of the magnetosheath plasma into the classes quasi‐parallel versus quasi‐perpendicular and foreshock/no foreshock (referring to the geometry of the upstream bow shock). We evaluate this method based on the magnetosheath measurements of the high‐energy ion energy flux, magnetic field standard deviation, and ion temperature anisotropy. We find that the method is promising and useful, in that it eliminates the uncertainties associated with propagating upstream measurements made far from the bow shock. Finally, we discuss some possible extensions of the methodology to be investigated in the future.
@article{10_1029_2021ja029269, title = {Classifying the Magnetosheath Behind the Quasi‐Parallel and Quasi‐Perpendicular Bow Shock by Local Measurements}, author = {Karlsson, T. and Raptis, S. and Trollvik, H. and Nilsson, H.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2021}, doi = {10.1029/2021JA029269}, url = {https://doi.org/10.1029/2021ja029269}, }
APA

Karlsson, T., Raptis, S., Trollvik, H., Nilsson, H.(2021). Classifying the Magnetosheath Behind the Quasi‐Parallel and Quasi‐Perpendicular Bow Shock by Local Measurements. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2021JA029269

BibTeX
```
@article{10_1029_2021ja029269,
  title = {Classifying the Magnetosheath Behind the Quasi‐Parallel and Quasi‐Perpendicular Bow Shock by Local Measurements},
  author = {Karlsson, T. and Raptis, S. and Trollvik, H. and Nilsson, H.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2021},
  doi = {10.1029/2021JA029269},
  url = {https://doi.org/10.1029/2021ja029269},
}
```
On the Generation of Pi2 Pulsations due to Plasma Flow Patterns Around Magnetosheath Jets

C. Katsavrias, S. Raptis, I.A. Daglis, T. Karlsson, M. Georgiou, and G. Balasis

Geophysical Research Letters, Mar 2021

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We report observations of a magnetosheath jet followed by a period of decelerated background plasma. During this period, THEMIS‐A magnetometer showed abrupt disturbances which, in the wavelet spectrum, appeared as prominent and irregular pulsations in two frequency bands (7.6–9.2 and 12–17 mHz) within the Pi2 range. The observations suggest—for the first time to our knowledge—that these pulsations were locally generated by the abrupt magnetic field changes driven by the jet’s interaction with the ambient magnetosheath plasma. Furthermore, similar pulsations, detected by THEMIS‐D inside the magnetosphere with a 140 s time‐lag (which corresponds to the propagation time of a disturbance traveling with Alfvénic speed), are shown to be directly associated with the ones in the magnetosheath, which raises the question of how exactly these pulsations are propagated through the magnetopause.
@article{10_1029_2021gl093611, title = {On the Generation of Pi2 Pulsations due to Plasma Flow Patterns Around Magnetosheath Jets}, author = {Katsavrias, C. and Raptis, S. and Daglis, I. A. and Karlsson, T. and Georgiou, M. and Balasis, G.}, journal = {Geophysical Research Letters}, year = {2021}, doi = {10.1029/2021GL093611}, url = {https://doi.org/10.1029/2021gl093611}, }
APA

Katsavrias, C., Raptis, S., Daglis, I. A., Karlsson, T., Georgiou, M., Balasis, G.(2021). On the Generation of Pi2 Pulsations due to Plasma Flow Patterns Around Magnetosheath Jets. Geophysical Research Letters. https://doi.org/10.1029/2021GL093611

BibTeX
```
@article{10_1029_2021gl093611,
  title = {On the Generation of Pi2 Pulsations due to Plasma Flow Patterns Around Magnetosheath Jets},
  author = {Katsavrias, C. and Raptis, S. and Daglis, I. A. and Karlsson, T. and Georgiou, M. and Balasis, G.},
  journal = {Geophysical Research Letters},
  year = {2021},
  doi = {10.1029/2021GL093611},
  url = {https://doi.org/10.1029/2021gl093611},
}
```
Causes of Jets in the Quasi‐Perpendicular Magnetosheath

P. Kajdič, S. Raptis, X. Blanco‐Cano, and T. Karlsson

Geophysical Research Letters, Mar 2021

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Magnetosheath jets are currently an important topic in the field of magnetosheath physics. It is thought that 97% of the jets are produced by the shock rippling at quasi‐parallel shocks. Recently, large statistical studies of magnetosheath jets have been performed, however, it is not clear whether rippling also produces jets found downstream of quasi‐perpendicular shocks. We analyze four types of events in the quasi‐perpendicular magnetosheath with signatures characteristic of magnetosheath jets, namely increased density and/or dynamic pressure that were not produced by the shock rippling: (a) magnetic flux tubes connected to the quasi‐parallel bow‐shock, (b) nonreconnecting current sheets, (c) reconnection exhausts, and (d) mirror‐mode waves. The flux tubes are downstream equivalents of the upstream traveling foreshocks. Magnetosheath jets can impact the magnetopause, so knowing the conditions under which they form may enable us to understand their signatures in the magnetosphere.
@article{10_1029_2021gl093173, title = {Causes of Jets in the Quasi‐Perpendicular Magnetosheath}, author = {Kajdič, P. and Raptis, S. and Blanco‐Cano, X. and Karlsson, T.}, journal = {Geophysical Research Letters}, year = {2021}, doi = {10.1029/2021GL093173}, url = {https://doi.org/10.1029/2021gl093173}, }
APA

Kajdič, P., Raptis, S., Blanco‐Cano, X., Karlsson, T.(2021). Causes of Jets in the Quasi‐Perpendicular Magnetosheath. Geophysical Research Letters. https://doi.org/10.1029/2021GL093173

BibTeX
```
@article{10_1029_2021gl093173,
  title = {Causes of Jets in the Quasi‐Perpendicular Magnetosheath},
  author = {Kajdič, P. and Raptis, S. and Blanco‐Cano, X. and Karlsson, T.},
  journal = {Geophysical Research Letters},
  year = {2021},
  doi = {10.1029/2021GL093173},
  url = {https://doi.org/10.1029/2021gl093173},
}
```
Magnetosheath jet evolution as a function of lifetime: global hybrid-Vlasov simulations compared to MMS observations

M. Palmroth, S. Raptis, J. Suni, T. Karlsson, L. Turc, A. Johlander, U. Ganse, Y. Pfau-Kempf, X. Blanco-Cano, M. Akhavan-Tafti, and 5 more authors

Annales Geophysicae, Mar 2021

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. Magnetosheath jets are regions of high dynamic pressure, which can traverse from the bow shock towards the magnetopause. Recent modelling efforts, limited to a single jet and a single set of upstream conditions, have provided the first estimations about how the jet parameters behave as a function of position within the magnetosheath. Here we expand the earlier results by doing the first statistical investigation of the jet dimensions and parameters as a function of their lifetime within the magnetosheath. To verify the simulation behaviour, we first identify jets from Magnetosphere Multiscale (MMS) spacecraft data (6142 in total) and confirm the Vlasiator jet general behaviour using statistics of 924 simulated individual jets. We find that the jets in the simulation are in quantitative agreement with the observations, confirming earlier findings related to jets using Vlasiator. The jet density, dynamic pressure, and magnetic field intensity show a sharp jump at the bow shock, which decreases towards the magnetopause. The jets appear compressive and cooler than the magnetosheath at the bow shock, while during their propagation towards the magnetopause they thermalise. Further, the shape of the jets flatten as they progress through the magnetosheath. They are able to maintain their flow velocity and direction within the magnetosheath flow, and they end up preferentially to the side of the magnetosheath behind the quasi-parallel shock. Finally, we find that Vlasiator jets during low solar wind Alfvén Mach number MA are shorter in duration, smaller in their extent, and weaker in terms of dynamic pressure and magnetic field intensity as compared to the jets during high MA.
@article{10_5194_angeo_39_289_2021, title = {Magnetosheath jet evolution as a function of lifetime: global hybrid-Vlasov simulations compared to MMS observations}, author = {Palmroth, M. and Raptis, S. and Suni, J. and Karlsson, T. and Turc, L. and Johlander, A. and Ganse, U. and Pfau-Kempf, Y. and Blanco-Cano, X. and Akhavan-Tafti, M. and Battarbee, M. and Dubart, M. and Grandin, M. and Tarvus, V. and Osmane, A.}, journal = {Annales Geophysicae}, year = {2021}, doi = {10.5194/angeo-39-289-2021}, url = {https://doi.org/10.5194/angeo-39-289-2021}, }
APA

Palmroth, M., Raptis, S., Suni, J., Karlsson, T., Turc, L., Johlander, A., Ganse, U., Pfau-Kempf, Y., Blanco-Cano, X., Akhavan-Tafti, M., Battarbee, M., Dubart, M., Grandin, M., Tarvus, V., Osmane, A.(2021). Magnetosheath jet evolution as a function of lifetime: global hybrid-Vlasov simulations compared to MMS observations. Annales Geophysicae. https://doi.org/10.5194/angeo-39-289-2021

BibTeX
```
@article{10_5194_angeo_39_289_2021,
  title = {Magnetosheath jet evolution as a function of lifetime: global hybrid-Vlasov simulations compared to MMS observations},
  author = {Palmroth, M. and Raptis, S. and Suni, J. and Karlsson, T. and Turc, L. and Johlander, A. and Ganse, U. and Pfau-Kempf, Y. and Blanco-Cano, X. and Akhavan-Tafti, M. and Battarbee, M. and Dubart, M. and Grandin, M. and Tarvus, V. and Osmane, A.},
  journal = {Annales Geophysicae},
  year = {2021},
  doi = {10.5194/angeo-39-289-2021},
  url = {https://doi.org/10.5194/angeo-39-289-2021},
}
```

2020

Helium in the Earth’s foreshock: a global Vlasiator survey

M. Battarbee, X. Blanco-Cano, L. Turc, P. Kajdič, A. Johlander, V. Tarvus, S. Fuselier, K. Trattner, M. Alho, T. Brito, and 9 more authors

Annales Geophysicae, Mar 2020

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. The foreshock is a region of space upstream of the Earth’s bow shock extending along the interplanetary magnetic field (IMF). It is permeated by shock-reflected ions and electrons, low-frequency waves, and various plasma transients. We investigate the extent of the He2+ foreshock using Vlasiator, a global hybrid-Vlasov simulation. We perform the first numerical global survey of the helium foreshock and interpret some historical foreshock observations in a global context. The foreshock edge is populated by both proton and helium field-aligned beams, with the proton foreshock extending slightly further into the solar wind than the helium foreshock and both extending well beyond the ultra-low frequency (ULF) wave foreshock. We compare our simulation results with Magnetosphere Multiscale (MMS) Hot Plasma Composition Analyzer (HPCA) measurements, showing how the gradient of suprathermal ion densities at the foreshock crossing can vary between events. Our analysis suggests that the IMF cone angle and the associated shock obliquity gradient can play a role in explaining this differing behaviour. We also investigate wave–ion interactions with wavelet analysis and show that the dynamics and heating of He2+ must result from proton-driven ULF waves. Enhancements in ion agyrotropy are found in relation to, for example, the ion foreshock boundary, the ULF foreshock boundary, and specular reflection of ions at the bow shock. We show that specular reflection can describe many of the foreshock ion velocity distribution function (VDF) enhancements. Wave–wave interactions deep in the foreshock cause de-coherence of wavefronts, allowing He2+ to be scattered less than protons.
@article{10_5194_angeo_38_1081_2020, title = {Helium in the Earth's foreshock: a global Vlasiator survey}, author = {Battarbee, M. and Blanco-Cano, X. and Turc, L. and Kajdič, P. and Johlander, A. and Tarvus, V. and Fuselier, S. and Trattner, K. and Alho, M. and Brito, T. and Ganse, U. and Pfau-Kempf, Y. and Akhavan-Tafti, M. and Karlsson, T. and Raptis, S. and Dubart, M. and Grandin, M. and Suni, J. and Palmroth, M.}, journal = {Annales Geophysicae}, year = {2020}, doi = {10.5194/angeo-38-1081-2020}, url = {https://doi.org/10.5194/angeo-38-1081-2020}, }
APA

Battarbee, M., Blanco-Cano, X., Turc, L., Kajdič, P., Johlander, A., Tarvus, V., Fuselier, S., Trattner, K., Alho, M., Brito, T., Ganse, U., Pfau-Kempf, Y., Akhavan-Tafti, M., Karlsson, T., Raptis, S., Dubart, M., Grandin, M., Suni, J., Palmroth, M.(2020). Helium in the Earth’s foreshock: a global Vlasiator survey. Annales Geophysicae. https://doi.org/10.5194/angeo-38-1081-2020

BibTeX
```
@article{10_5194_angeo_38_1081_2020,
  title = {Helium in the Earth's foreshock: a global Vlasiator survey},
  author = {Battarbee, M. and Blanco-Cano, X. and Turc, L. and Kajdič, P. and Johlander, A. and Tarvus, V. and Fuselier, S. and Trattner, K. and Alho, M. and Brito, T. and Ganse, U. and Pfau-Kempf, Y. and Akhavan-Tafti, M. and Karlsson, T. and Raptis, S. and Dubart, M. and Grandin, M. and Suni, J. and Palmroth, M.},
  journal = {Annales Geophysicae},
  year = {2020},
  doi = {10.5194/angeo-38-1081-2020},
  url = {https://doi.org/10.5194/angeo-38-1081-2020},
}
```
Classifying Magnetosheath Jets Using MMS: Statistical Properties

S. Raptis, T. Karlsson, F. Plaschke, A. Kullen, and P. Lindqvist

Journal of Geophysical Research: Space Physics, Mar 2020

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Using Magnetospheric Multiscale (MMS) data, we find, classify, and analyze transient dynamic pressure enhancements in the magnetosheath (jets) from May 2015 to May 2019. A classification algorithm is presented, using in situ MMS data to classify jets ( ) into different categories according to their associated angle between interplanetary magnetic field (IMF) and the bow shock normal vector (θBn). Jets appearing for θBn < 45 are referred to as quasi‐parallel, while jets appearing for θBn > 45 as quasi‐perpendicular jets. Furthermore, we define those jets that occur at the boundaries between quasi‐parallel and quasi‐perpendicular magnetosheath as boundary jets. Finally, encapsulated jets are jet‐like structures with similar characteristics to quasi‐parallel jets while the surrounding plasma is of quasi‐perpendicular nature. We present the first statistical results of such a classification and provide comparative statistics for each class. Furthermore, we investigate correlations between jet quantities. Quasi‐parallel jets have the highest dynamic pressure while occurring more often than quasi‐perpendicular jets. The infrequent quasi‐perpendicular jets have a much smaller duration, velocity, and density and are therefore relatively weaker. We conclude that quasi‐parallel and boundary jets have similar properties and are unlikely to originate from different generation mechanisms. Regarding the encapsulated jets, we suggest that they are a special subset of quasi‐parallel jets originating from the flanks of the bow shock, for large IMF cone angles although a relation to flux transfer events (FTEs) and magnetospheric plasma is also possible. Our results support existing generation theories, such as the bow shock ripple and SLAMS‐associated mechanisms while indicating that other factors may contribute as well.
@article{10_1029_2019ja027754, title = {Classifying Magnetosheath Jets Using MMS: Statistical Properties}, author = {Raptis, S. and Karlsson, T. and Plaschke, F. and Kullen, A. and Lindqvist, P.}, journal = {Journal of Geophysical Research: Space Physics}, year = {2020}, doi = {10.1029/2019JA027754}, url = {https://doi.org/10.1029/2019ja027754}, }
APA

Raptis, S., Karlsson, T., Plaschke, F., Kullen, A., Lindqvist, P.(2020). Classifying Magnetosheath Jets Using MMS: Statistical Properties. Journal of Geophysical Research: Space Physics. https://doi.org/10.1029/2019JA027754

BibTeX
```
@article{10_1029_2019ja027754,
  title = {Classifying Magnetosheath Jets Using MMS: Statistical Properties},
  author = {Raptis, S. and Karlsson, T. and Plaschke, F. and Kullen, A. and Lindqvist, P.},
  journal = {Journal of Geophysical Research: Space Physics},
  year = {2020},
  doi = {10.1029/2019JA027754},
  url = {https://doi.org/10.1029/2019ja027754},
}
```

Classification of Magnetosheath Jets Using Neural Networks and High Resolution OMNI (HRO) Data

S. Raptis, S. Aminalragia-Giamini, T. Karlsson, and M. Lindberg

Frontiers in Astronomy and Space Sciences, Mar 2020

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Research Topic: Machine Learning in Heliophysics

@article{10_3389_fspas_2020_00024,
  title = {Classification of Magnetosheath Jets Using Neural Networks and High Resolution OMNI (HRO) Data},
  author = {Raptis, S. and Aminalragia-Giamini, S. and Karlsson, T. and Lindberg, M.},
  journal = {Frontiers in Astronomy and Space Sciences},
  year = {2020},
  doi = {10.3389/fspas.2020.00024},
  url = {https://doi.org/10.3389/fspas.2020.00024},
}

APA

Raptis, S., Aminalragia-Giamini, S., Karlsson, T., Lindberg, M.(2020). Classification of Magnetosheath Jets Using Neural Networks and High Resolution OMNI (HRO) Data. Frontiers in Astronomy and Space Sciences. https://doi.org/10.3389/fspas.2020.00024

BibTeX

@article{10_3389_fspas_2020_00024,
  title = {Classification of Magnetosheath Jets Using Neural Networks and High Resolution OMNI (HRO) Data},
  author = {Raptis, S. and Aminalragia-Giamini, S. and Karlsson, T. and Lindberg, M.},
  journal = {Frontiers in Astronomy and Space Sciences},
  year = {2020},
  doi = {10.3389/fspas.2020.00024},
  url = {https://doi.org/10.3389/fspas.2020.00024},
}

Current Sheet Statistics in the Magnetosheath

E. Yordanova, Z. Vörös, S. Raptis, and T. Karlsson

Frontiers in Astronomy and Space Sciences, Mar 2020

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Research Topic: Improving the Understanding of Kinetic Processes in Solar Wind and Magnetosphere: From CLUSTER to MMS

@article{10_3389_fspas_2020_00002,
  title = {Current Sheet Statistics in the Magnetosheath},
  author = {Yordanova, E. and Vörös, Z. and Raptis, S. and Karlsson, T.},
  journal = {Frontiers in Astronomy and Space Sciences},
  year = {2020},
  doi = {10.3389/fspas.2020.00002},
  url = {https://doi.org/10.3389/fspas.2020.00002},
}

APA

Yordanova, E., Vörös, Z., Raptis, S., Karlsson, T.(2020). Current Sheet Statistics in the Magnetosheath. Frontiers in Astronomy and Space Sciences. https://doi.org/10.3389/fspas.2020.00002

BibTeX

@article{10_3389_fspas_2020_00002,
  title = {Current Sheet Statistics in the Magnetosheath},
  author = {Yordanova, E. and Vörös, Z. and Raptis, S. and Karlsson, T.},
  journal = {Frontiers in Astronomy and Space Sciences},
  year = {2020},
  doi = {10.3389/fspas.2020.00002},
  url = {https://doi.org/10.3389/fspas.2020.00002},
}