The solar wind velocity monitor at the Sun-Earth L1 point (SOHO, ACE, DSCOVR) has been used to estimate the arrival time of interplanetary (IP) shocks associated with coronal mass ejections (CMEs) and corotating interaction regions (CIRs).  In this estimate, the radial propagation speed of the IP shock is assumed to be the same as the measured solar wind (proton) speed.  However, near the Sun, the CME front identified by SOHO LASCO imager sometimes propagates at velocity >1000 km/s, being faster than solar wind velocity measured at L1 (e.g., Tokumaru et al., 2006).  Even after considering the deceleration of CME propagation with distance, these two speeds at 1 AU are not guaranteed to be the same.

We compared these speeds: between the solar wind and the radial propagation of the IP shock front.  We used SOHO and ACE spacecraft data for the velocity and IP shock timing at L1, and geomagnetic data (geomagnetic sudden commencement: SC) for the IP shock timing at the Earth.  We examined about 400 IP shock events that are consistent between SOHO and ACE during more than two solar cycles.  We found the following tendency.
(1) The estimated arrival time driven from geomagnetic SC is often quite different from expected arrival time of the IP shock from the L1 velocity measurement. 
(2) The estimated propagation velocity of the IP shock was from 80% to > 200% of the solar wind velocity.
(3) For a majority of the cases, the SC-estimated propagation velocity is slightly faster than the measured solar wind proton velocity, and is rather close to the velocity of the solar wind alpha particle.

The upcoming SMILE mission will give extra dataset for the arrival of the IP shock for further study.

How to cite: Yokoyama, Y., Yamauchi, M., Kotani, T., and Matzka, J.: Large difference in radial speed between the interplanetary (IP) shock propagation and the solar wind near the Earth., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11891, https://doi.org/10.5194/egusphere-egu26-11891, 2026.

Long-lasting quasi-radial interplanetary magnetic field (IMF) events represent a distinct class of solar wind conditions characterized by an unusual magnetic field orientation. Unlike typical solar wind intervals, these events deviate significantly from the nominal Parker spiral configuration, leading to altered large-scale spatial correlations of the IMF. In this study, we investigate the spatial correlation characteristics of long-lasting quasi-radial IMF events and compare them with those observed during normal Parker spiral conditions. Quasi-radial IMF events are identified using the criterion Bx / B >0.9 sustained for more than 4 hours, following a definition similar to that adopted in previous studies. Applying this criterion to Wind magnetic field observations from 2001 to 2024, we identify a total of 753 long-lasting quasi-radial IMF events. We calculate correlation coefficients between Wind and ACE magnetic field measurements without applying a time shift, thereby focusing on the intrinsic spatial correlation rather than propagation effects. The correlation analysis is performed for multiple magnetic field parameters, with particular emphasis on the magnetic field magnitude. Our results indicate that, during quasi-radial IMF conditions, the correlation coefficient of the magnetic field magnitude exceeds that of typical Parker spiral intervals when the spacecraft separation distance is greater than approximately 30 Re. However, within the intermediate separation range of roughly 30–150 Re, the correlation values are generally lower than those observed during Parker spiral conditions, suggesting a scale-dependent modification of IMF coherence under quasi-radial configurations. These findings imply that long-lasting quasi-radial IMF events exhibit distinct spatial correlation behaviors compared to nominal solar wind conditions, potentially reflecting differences in solar wind structure, turbulence properties, or magnetic field topology.

How to cite: Pi, G., Nemecek, Z., and Safrankova, J.: Correlation coefficient of long-lasting quasi-radial IMF events , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5423, https://doi.org/10.5194/egusphere-egu26-5423, 2026.

Plasma structures with the enhanced dynamic pressure, density, and/or bulk speed, commonly referred to as magnetosheath (MSH) jets, can be detected downstream of both quasi-perpendicular and quasi-parallel bow shocks. Although their presence in the MSH is well established, their true three-dimensional morphology, internal structure, and characteristic scales remain under active debate. Recent simulation results, suggesting filamentary interconnected jet structures, contrast with the simplified “pancake” or cylindrical geometries often inferred from single-spacecraft observations, highlighting the need of multi-point studies.

We present case studies of complex structure of MSH jets using coordinated measurements of THEMIS, MMS, and other missions. We focus on their spatial structure and temporal evolution as they propagate through the MSH, with attention to multi-spacecraft signatures in plasma and magnetic field parameters. Rather than drawing general conclusions, this work aims to illustrate the capabilities and limitations of multi-spacecraft observations for determination of jet morphology and evolution. We try to place individual events into the broader context of ongoing discussions. Particular attention is given to the interaction of the MSH jet with the magnetopause and its role in (localized) boundary dynamics.

How to cite: Grygorov, K., Goncharov, O., Safrankova, J., and Nemecek, Z.: Magnetosheath jets: morphology and evolution from multi-spacecraft observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8064, https://doi.org/10.5194/egusphere-egu26-8064, 2026.

Plasma structures with enhanced dynamic pressure, density or speed are often observed in Earth’s magnetosheath. These structures, known as jets and fast plasmoids, can be registered in the magnetosheath, downstream of both the quasi-perpendicular and quasi-parallel bow shocks Using measurements by the Magnetospheric Multiscale (MMS) spacecraft, Goncharov et al., (2020) showed similarities in the plasma properties of the jets and fast plasmoids. On the other hand, they pointed out that the different magnetic fields inside the structures suggest that the formation mechanisms are not the same. Previous studies established that foreshock structures can be a source of the jets (Raptis et al., 2022). Xirogiannopoulou et al. (2024) found that the subsolar foreshock contains several types of structures with enhanced density or/and magnetic field magnitude, like plasmoids, SLAMS and mixed structures. Following these results, we use multi-spacecraft data collected by THEMIS, Cluster, Magnetospheric Multiscale Spacecraft (MMS) and OMNI missions, and present analytical multi-spacecraft statistical and case studies on the connection between the activity around the bow shock. Based on our comparative analysis, we discuss features of jet-like structures, and their relation to the different phenomena in the foreshock.

How to cite: Goncharov, O., Xirogiannopoulou, N., Balot, P., Grygorov, K., Safrankova, J., Nemecek, Z., and Hajos, M.: Connection of the magnetosheath jet-like structures with foreshock activities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4405, https://doi.org/10.5194/egusphere-egu26-4405, 2026.

Plasma waves play a central role in the solar wind–magnetosphere interaction, especially in the foreshock and magnetosheath, where reflected particles, shock processes, and turbulence shape their properties. While these regions have been widely studied, the way foreshock waves evolve as they encounter the bow shock and how their downstream signatures relate to the upstream conditions remain poorly understood. Using multi-spacecraft observations from the MMS and/or THEMIS missions, we examine wave activity in the foreshock and characterize their key properties and put our findings in context with previous statistical results. We also present a statistical analysis of wave activity in the magnetosheath and compare it with the simultaneous measurements in both regions to explore how wave signatures change across the bow shock. This approach provides a more complete picture of how plasma waves vary across regions and offers new insight into their evolution in the near-Earth environment.

How to cite: Balot, P., Goncharov, O., Safrankova, J., Nemecek, Z., Xirogiannopoulou, N., and Grygorov, K.: Statistical study of wave activity in the foreshock and magnetosheath regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5486, https://doi.org/10.5194/egusphere-egu26-5486, 2026.

The Bernoulli principle, a fundamental concept in fluid dynamics, occupies an important position in the development of the discipline and finds wide application in both theory and engineering practice. In space plasmas, the Bernoulli equation can be derived from the continuity equation and the energy conservation equation. This presentation analyzes and presents the general form of the Bernoulli equation for multicomponent, non-equilibrium, and anisotropic space plasmas. Based on in-situ measurements from spacecraft such as ACE and MMS, this study examines the quantitative relationship between the plasma upstream (solar wind) and downstream (magnetosheath) of the Earth's bow shock. It confirms the applicability of Bernoulli’s theorem across the bow shock under both high-speed and low-speed solar wind conditions, demonstrating the existence of a conserved quantity—the characteristic energy of particles—along plasma streamlines. This indicates that Bernoulli’s theorem serves as an important theoretical tool for analyzing energy conversion processes across the bow shock and reveals a universal invariant—the particle characteristic energy—present in the upstream solar wind and throughout the downstream magnetosheath region. Applying Bernoulli’s theorem to the theoretical analysis of the relationship between solar coronal temperature and planetary magnetosheath temperature yields a quantitative relation that is consistent with statistical analyses of observational data from spacecraft such as MESSENGER, MMS, Voyager 2, and Cassini regarding thermodynamic parameters like the magnetosheath temperatures of planets (Mercury, Earth, Jupiter, and Saturn). These results hold significant value for studying the energy transfer mechanisms from the solar wind to magnetospheres and for understanding space weather in planetary magnetospheres

How to cite: Shen, C.: Bernoulli's Theorem in Space Plasmas and Its Applications, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17159, https://doi.org/10.5194/egusphere-egu26-17159, 2026.

The May 2024 geomagnetic superstorm was one of the most extreme space weather events of the past two decades. Starting from the Sun, a group of sunspots had grown significantly, producing a substantial solar flare and launching six coronal mass ejections (CMEs) and reaching the Earth, they significantly affected the Earth's magnetosphere. The Shue et al. (1998) model predicts the magnetopause position at a minimum distance of ~4 Re during the main phase of a storm, while the MHD (SWMF) model predicts a minimum at ~3.3 Re. To validate these models, we manually identified the magnetopause crossings observed by THEMIS, GOES, and MMS during the storm period. The crossings are identified by examining the multispacecraft data, and the impact of extreme conditions on the magnetopause location is determined. The observation and the Shue et al. (1998) model suggest that the magnetopause is compressed from 10 Re to 4 Re in a period of no more than 20 minutes. The manual identification from the multi-spacecraft data assumes that the magnetopause location is approximately 5 Re, and this result is consistent with predictions using various models. Moreover, the normal of each magnetopause crossing and its difference between the predicted normal from the Shue et al. (1998) model were calculated. The results can provide key insights into the dynamic magnetopause under extreme conditions.

How to cite: Ghosh, M., Wang, D., Haas, B., Lyu, X., Pi, G., Nemecek, Z., and Safrankova, J.: Validation of magnetopause positions predicted by models against multi-mission magnetopause crossings for the May 2024 superstorm, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5547, https://doi.org/10.5194/egusphere-egu26-5547, 2026.

The subsolar standoff distance r₀ of Earth's magnetopause is a key parameter in understanding the interaction between the solar wind and the magnetosphere. Despite decades of modeling efforts, significant uncertainties persist between model predictions and satellite observation of the magnetopause location. This study introduces a new data-driven parameterization of r₀, based on a dataset containing over 220,000 dayside magnetopause crossings obtained by the THEMIS (2007-2022) and Cluster (2001-2020) missions. Four established magnetopause models are benchmarked against this dataset by computing the difference between predicted and observed r₀, yielding root-mean-square errors (RMSE) of > 1 R_E globally and > 0.8 R_E in the subsolar region. Since different models use a variety of input parameters, it remains uncertain which parameters are most suitable to model the subsolar standoff distance of Earth's magnetopause to date. To address this question, a machine learning approach is used: an XGBoost regression model is trained and interpreted using SHapley Additive exPlanation (SHAP) values. The solar wind dynamic pressure is found to be the dominant contributor, followed by geomagnetic indices (AE, SYMH), interplanetary magnetic field (IMF) magnitude, dipole tilt angle, and IMF cone angle. The IMF B_z component contributes only marginally when geomagnetic indices are included. A support vector regression (SVR) model using the mentioned parameters achieves a RMSE of 0.68 R_E, improving on the best analytic model by approximately 17%.  To allow for straightforward modeling of the subsolar standoff distance, a second-order polynomial expression with 14 terms is derived, providing a compact, interpretable, and accurate representation of r₀. We note that the SVR model and the polynomial representation is not able to predict r₀ for extreme input conditions, e.g., during periods of very high solar wind dynamic pressure that is caused by, e.g., the passage of interplanetary coronal mass ejections. Accordingly, the parameter ranges that define the validity domain of the models are specified. We plan to broaden the range of possible input parameters in future iterations to account for, e.g., storm conditions as well. The presented results offer improved predictive accuracy of the subsolar standoff distance and highlight the potential of so far unconsidered parameters and rarely used techniques in modeling Earth's magnetopause.

How to cite: Klingenstein, L., Grimmich, N., Shprits, Y. Y., Grison, B., Lyu, X., Pöppelwerth, A., Wang, D., and Plaschke, F.: Parameterization of the Subsolar Standoff Distance of Earth’s Magnetopause based on Results from Machine Learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7269, https://doi.org/10.5194/egusphere-egu26-7269, 2026.

The Earth’s magnetopause is the boundary separating the terrestrial and the interplanetary magnetic field. Variations in solar wind pressure, as well as structures originating in the solar wind and foreshock regions, induce continuous motion of this boundary. In addition, strong velocity shear between magnetosheath and magnetospheric plasmas can trigger the Kelvin–Helmholtz instability. These processes can generate waves on the magnetopause that play a key role in governing mass transport and energy transfer between the solar wind and the magnetosphere.

Accurate estimation of the magnetopause wave vector is important for understanding interactions at the boundary. In this study, we compare different techniques for wave vector estimation. (1) Single-spacecraft methods require the determination of the boundary normal direction using approaches such as minimum variance analysis of the magnetic field (MVAB) or minimization of the Faraday residue (MFR), combined with estimates of the magnetopause phase velocity derived from ion measurements. (2) Cross-correlation analysis of magnetic field, density, and temperature measurements between different spacecraft allows estimation of wave vectors. In this context, modelling is used to explore potential systematic errors, for example arising from asymmetric waves, and to assess uncertainties in time-lag determination. (3) The wave telescope represents an alternative multi-spacecraft method to determine the wave vector.

Using observations from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, we apply these methods to several magnetopause wave events. We present preliminary results of this comparison, providing insight into the respective limitations and uncertainties.

How to cite: Pöppelwerth, A., Grimmich, N., Schulz, L., Klingenstein, L., and Plaschke, F.: Magnetopause surface waves: A comparison of wave vector determination techniques using THEMIS observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12517, https://doi.org/10.5194/egusphere-egu26-12517, 2026.

Sub-Alfvénic flows have been observed within magnetic clouds of interplanetary Coronal Mass Ejections (ICMEs), where enhanced magnetic field strength coincides with low plasma density. These conditions can significantly change the planetary space environment by enabling direct interaction between sub-Alfvénic solar wind and a planet’s magnetosphere. To investigate this regime, we perform a 3D global simulation using the hybrid code MENURA, modeling a plasma flow that transitions from super-Alfvénic to sub-Alfvénic as it encounters the magnetosphere. The upstream Alfvén speed is varied using a smoothed, step-like analytical function under pressure balance. The interplanetary magnetic field is oriented perpendicular to the Sun–planet direction, representative of local magnetic cloud conditions within ICMEs at 1AU. Our results reveal significant magnetospheric changes under sub-Alfvénic solar wind conditions: The bow shock rapidly weakens and dissipates while expanding to distances well beyond its original subsolar position, with pronounced expansion along the flanks. These findings provide new insight into magnetospheric dynamics under varying solar wind regimes and improve our understanding of planetary plasma environments. Furthermore, they offer valuable context for interpreting past observations from the MESSENGER mission and ongoing measurements from ESA’s BepiColombo mission.

How to cite: Preisser, L., Pucci, F., Ballerini, G., Henri, P., Sporykhin, F., and Wedlund, C. S.: Sub-Alfvénic solar wind interaction with a magnetosphere: 3D hybrid simulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22070, https://doi.org/10.5194/egusphere-egu26-22070, 2026.

Coherent structures and random plasma variability at intermediate scales—between the large heliospheric structures such as interplanetary coronal mass ejections (ICMEs) and kinetic scales—have attracted growing attention within the solar wind and ICME community. This mesoscale variability in the solar wind has been shown to introduce uncertainty in the prescribed driving conditions of the magnetosphere, as in situ spacecraft upstream of the Earth’s magnetosphere do not always represent the actual solar wind forcing.  Here, we demonstrate the global magnetospheric impacts of ICME mesoscale magnetic field variations. Using the Geospace configuration of the Space Weather Modelling Framework, we simulate the magnetospheric environment and, for the first time, capture a non-linear magnetospheric response that results from differences in the time-history of the driving conditions. Our results highlight the importance of understanding the longitudinal mesoscale variations in the solar wind to accurately interpret magnetospheric dynamics resulting from solar wind energy input into the system.

How to cite: Ala-Lahti, M., Pulkkinen, T., Brenner, A., Keebler, T., and Kilpua, E.: The global magnetospheric impacts of ICME mesoscale magnetic field variations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10518, https://doi.org/10.5194/egusphere-egu26-10518, 2026.