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The Martian bow shock stands as the first defense against the solar wind and shapes the Martian magnetosphere. Previous studies showed the correlation between the Martian bow shock location and solar wind parameters. Here we present direct evidence of solar wind effects on the Martian bow shock by analyzing Tianwen‐1 and MAVEN data. We examined three cases where Tianwen‐1 data show rapid oscillations of the bow shock, while MAVEN data record changes in solar wind plasma and magnetic field. The results indicate that the bow shock is rapidly compressed and then expanded during the dynamic pressure pulse in the solar wind, and is also oscillated during the IMF rotation. The superposition of variations in multiple solar wind parameters leads to more intensive bow shock oscillation. This study emphasizes the importance of joint observations by Tianwen‐1 and MAVEN for studying the real‐time response of the Martian magnetosphere to the solar wind. Plain Language Summary The Martian bow shock is a standing shock wave that forms ahead of Mars due to the interaction with the solar wind, where the supersonic solar wind flow drops sharply to subsonic. The bow shock plays a crucial role in shaping the Martian magnetosphere and controlling the energy, mass, and momentum exchange between the solar wind and the Martian atmosphere. Previous research has shown that the position of Mars' bow shock is related to the solar wind. This research presents two‐spacecraft observations of how the solar wind affects the Martian bow shock. By analyzing data obtained by two orbiters, Tianwen‐1 and MAVEN, we find that the bow shock quickly contracts when the solar wind dynamic pressure rises or when the interplanetary magnetic field direction turns radial. When there are multiple changes in the solar wind at the same time, the bow shock moves around even more. This study shows how important it is to look at data from Tianwen‐1 and MAVEN at the same time to understand how Mars' magnetosphere reacts to the solar wind. Key Points First observations of the real‐time response of the Martian bow shock to changes in the upstream solar wind Direct evidence of the compression of the Martian bow shock under increased solar wind dynamic pressure Direct evidence of motion of the Martian bow shock caused by the rotation of the interplanetary magnetic field

Solar wind drives magnetospheric dynamics through coupling with the geospace system at the magnetopause. While upstream fluctuations correlate with geomagnetic activity, their impact on the magnetopause energy transfer is an open question. In this study, we examine three‐dimensional global magnetospheric simulations using the Geospace configuration of the Space Weather Modeling Framework. We examine the effects of solar wind fluctuations during a substorm event by running the model with four different driving conditions that vary in fluctuation frequency spectrum. We demonstrate that upstream fluctuations intensify the energy exchange at the magnetopause increasing both energy flux into and out of the system. The increased energy input is reflected in ground magnetic indices. Moreover, the fluctuations impact the magnetopause dynamics by regulating the energy exchange between the polar caps and lobes and energy transport within the magnetotail neutral sheet. Plain Language Summary Earth's magnetic field shields the near‐Earth space plasma environments from the direct influence of solar wind. Solar wind however drives the magnetosphere when physical processes at the magnetopause boundary enable the transfer of energy between the plasmas. The coupling has global consequences in the magnetosphere system and its efficiency is particularly dependent on the orientation of interplanetary magnetic field and its magnitude but also on magnetic field fluctuation power. We capture the impact of upstream fluctuations on magnetopause energy exchange and nightside magnetotail dynamics by analyzing magnetohydrodynamic simulations of the global magnetosphere using various upstream driving conditions. We discover that more energy flows out from and into the system at the magnetopause when the upstream solar wind plasma include magnetic field fluctuations. The upstream fluctuation power is moreover reflected in nightside magnetotail, where flow patterns at the neutral sheet are regulated, as well as to ground indices with fluctuations driving a stronger geomagnetic response. Key Points Solar wind magnetic field ULF fluctuations (2–8 mHz) increase energy transfer at the magnetopause boundary and into the inner magnetosphere The upstream fluctuations regulate the lobe dynamics and plasma flows at the magnetotail neutral current sheet The varying lobe and nightside dynamics are reflected in ground indices with solar wind fluctuations driving a stronger geomagnetic response

Ala‐Lahti et al. (2024, https://doi.org/10.1029/2024GL112922) present results from a global magnetohydrodynamic simulation of a single geomagnetic substorm for four scenarios: the original solar wind conditions, smoothed low‐frequency solar wind conditions, constant solar wind conditions with a boxcar averaged north/south component of the interplanetary magnetic field (IMF), and the boxcar‐averaged scenario with ultra‐low‐frequency (ULF) fluctuations. Smoothed (<1 mHz) solar wind parameters capture the bulk of the interaction, boxcar averaging reduces the energy flow through the system by 15%–40%, and ULF fluctuations (2–8 mHz) only enhance interactions by 5%–15%. From this, we conclude that low‐frequency plasma and magnetic field variations dominate the interaction. Further global simulations and observational studies of different events will be needed to determine the significance of intrinsic magnetopause and magnetotail instabilities (rather than directly driven interplanetary magnetic field fluctuations). They will also be needed to generalize these results for the full range of solar wind and geomagnetic conditions. Plain Language Summary All of the energy that powers geomagnetic storms and substorms originates in the solar wind and crosses the magnetopause to enter the magnetosphere. Much of this energy is stored within the magnetotail for subsequent release. The processes governing energy transfer at the magnetopause and in the magnetotail may be transient or continuous. If transient, they may occur in response to intrinsic local instabilities or be driven by fluctuations in upstream solar wind parameters. Ala‐Lahti et al. (2024, https://doi.org/10.1029/2024GL112922) test the latter hypothesis and find that ultra‐low‐frequency fluctuations in the interplanetary magnetic field enhance energy flows by only 5%–15%. By contrast, smoothed, low‐frequency variations in solar wind plasma and magnetic field parameters capture almost all the overall interaction. Further work is needed to generalize these results for a broader range of solar wind conditions, to examine the role of intrinsic instabilities at the magnetopause and in the magnetotail, and to validate the predictions with global observations. Key Points Smoothed solar wind plasma and magnetic field observations suffice to capture the bulk of the solar wind‐magnetosphere interaction Ultra‐low‐frequency fluctuations in the interplanetary magnetic field enhance the interaction by 5%–15% Global simulations, imaging, and in situ observations are needed to generalize and validate these results

The equatorward contraction of tropical precipitation, commonly referred to as the “deep‐tropical contraction”, is witnessed in the paleoclimate simulations of the early Eocene. However, the mechanism driving this contraction is still unclear. Based on the energetics framework of the Intertropical Convergence Zone (ITCZ) and the decomposition method of the latent heat flux along with the simulations of a climate system model, CESM1.2, we proposed a novel mechanism responsible for the “deep‐tropical contraction” in the early Eocene. The greenhouse gases‐induced sea surface warming amplifies the sensitivity of evaporation to surface wind speed changes through Clausius‐Clapeyron scaling, leading to an interhemispheric asymmetric enhancement of the latent heat flux. To maintain hemispheric energy balance, the cross‐equatorial atmospheric energy transport must be reduced during the solstice seasons. As a result, the solstitial location of the ITCZ shifts equatorward, causing the “deep‐tropical contraction” in the early Eocene. Plain Language Summary The early Eocene is the warmest epoch in the last 65 million years, with a global mean temperature 9°C–23°C higher than the preindustrial period. According to state‐of‐the‐art climate models, the tropical rainfall contracted toward the equator during this extremely warm period. However, the physical mechanism causing this phenomenon remains unclear. In this study, we examined the hemispheric energy balance in the early Eocene that causes the equatorward contraction of tropical precipitation. A novel mechanism underlying this phenomenon is revealed. Based on the climate modeling of CESM1.2, we show that the GHG‐induced warmth enhances the sensitivity of evaporation to surface wind speed changes in the early Eocene. Thus, the stronger tropical trade wind in the winter hemisphere will drive out stronger latent heat flux than in the summer hemisphere. This interhemispheric asymmetric response reduces the interhemispheric heating contrast in the solstice seasons. As a result, the ascending motion in the tropical atmosphere migrates toward the equator, finally decreases the width of tropical precipitation in the early Eocene. Key Points The “deep tropical contraction” in the early Eocene is caused by the equatorward migration of the seasonal ITCZ The equatorward migration of the solstitial ITCZ location in the early Eocene is due to decreased cross‐equatorial energy transport The enhanced wind‐evaporation effect in the early Eocene reduces the cross‐equatorial atmospheric energy transport in the solstitial seasons

Using the 8.5‐year Venus Express measurements, we demonstrate the asymmetric plasma distributions in the Venusian magnetosheath. An escaping plume is formed by pickup oxygen ions in the hemisphere where the motional electric field points outward from Venus, while the velocity of solar wind protons is faster in the opposite hemisphere. The pickup O+ escape rate is estimated to be (3.6 ± 1.4) × 1024 s−1 at solar maximum, which is comparable to the ion loss rate through the magnetotail, and (1.3 ± 0.4) × 1024 s−1 at solar minimum. The increase of O+ fluxes with extreme ultraviolet (EUV) intensity is significant upstream of the bow shock, partially attributed to the increase of exospheric neutral oxygen density. However, the solar wind velocity just has a slight effect on the pickup O+ escape rate in the magnetosheath, while the effect of solar wind density is not observed. Our results suggest the pickup O+ escape rate is mainly controlled by EUV radiation. Plain Language Summary The atmospheric evolution and water escape of Venus might be influenced by the solar wind‐Venus interaction. The atoms outside the induced magnetosphere are ionized by the solar radiation and accelerated to the escape velocity by solar wind electric field. In this way, the oxygen ions are picked up by solar wind and lost from the atmosphere to space. We use the data from Venus Express spacecraft to analyze the distribution of pickup oxygen ions in the vicinity of the planet. The planetary oxygen ions form a strong escaping plume, indicating the pickup process is an efficient escape channel removing the atmospheric particles. With an enhanced solar extreme ultraviolet radiation, the escape rate through this channel would be higher because more ions are produced and then picked up. This indicates an enhanced ion loss billions of years ago since the young Sun is more active, which might be a reason for the disappearance of a presumably‐existed ocean. Key Points The pickup O+ escape rate at Venus increases with solar activity, and it is comparable to the ion loss rate through the magnetotail The solar wind velocity has a slight effect on the pickup O+ escape rate in the magnetosheath The neutral oxygen density upstream of the bow shock might increase by a factor of two from solar minimum to maximum

Coronal mass ejections (CMEs) are primary drivers of space weather, and studying their evolution in the inner heliosphere is vital to prepare for a timely response. Solar wind streams, acting as background, influence their propagation in the heliosphere and associated geomagnetic storm activity. This study introduces SWASTi-CME, a newly developed MHD-based CME model integrated into the Space Weather Adaptive SimulaTion (SWASTi) framework. It incorporates a nonmagnetized elliptic cone and a magnetized flux rope CME model. To validate the model’s performance with in situ observation at L1, two Carrington rotations were chosen: one during solar maxima with multiple CMEs, and one during solar minima with a single CME. The study also presents a quantitative analysis of CME–solar wind interaction using this model. To account for ambient solar wind effects, two scenarios of different complexity in solar wind conditions were established. The results indicate that ambient conditions can significantly impact some of the CME properties in the inner heliosphere. We found that the drag force on the CME front exhibits a variable nature, resulting in asymmetric deformation of the CME leading edge. Additionally, the study reveals that the impact on the distribution of CME internal pressure primarily occurs during the initial stage, while the CME density distribution is affected throughout its propagation. Moreover, regardless of the ambient conditions, it was observed that, after a certain propagation time (t), the CME volume follows a nonfractal power-law expansion (∝t 3.03−3.33) due to the attainment of a balanced state with ambient.

Mercury has a unique and complex space environment with its weak global magnetic field, intense solar wind, tenuous exosphere, and magnetospheric plasma particles. This complex system makes Mercury an excellent science target to understand effects of the solar wind to planetary environments. In addition, investigating Mercury’s dynamic magnetosphere also plays a key role to understand extreme exoplanetary environment and its habitability conditions against strong stellar winds. BepiColombo, a joint mission to Mercury by the European Space Agency and Japan Aerospace Exploration Agency, will address remaining open questions using two spacecraft, Mio and the Mercury Planetary Orbiter. Mio is a spin-stabilized spacecraft designed to investigate Mercury’s space environment, with a powerful suite of plasma instruments, a spectral imager for the exosphere, and a dust monitor. Because of strong constraints on operations during its orbiting phase around Mercury, sophisticated observation and downlink plans are required in order to maximize science outputs. This paper gives an overview of the Mio spacecraft and its mission, operations plan, and data handling and archiving.

Total solar eclipses (TSEs) provide a unique opportunity to observe the large-scale solar corona. The solar wind plays an important role in forming the large-scale coronal structure, and magnetohydrodynamic (MHD) simulations are used to reproduce it for further studying coronal mass ejections (CMEs). We conduct a data-constrained MHD simulation of the global solar corona including solar wind effects of the 2024 April 8 TSE with observed magnetograms using the message-passing interface adaptive mesh refinement versatile advection code (MPI-AMRVAC) within 2.5 R⊙. This TSE happened within the solar maximum, hence the global corona was highly structured. Our MHD simulation includes the energy equation with a reduced polytropic index γ = 1.05. We compare the global magnetic field for multiple magnetograms and use synchronic frames from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager to initialize the magnetic field configuration from a magnetofrictionally equilibrium solution, called the outflow field. We detail the initial and boundary conditions employed to time-advance the full set of ideal MHD equations such that the global corona is relaxed to a steady state. The magnetic field, the velocity field, and distributions of the density and thermal pressure are successfully reproduced. We demonstrate direct comparisons with TSE images in white light and Fe XIV emission augmented with quasi-separatrix layers, the integrated current density, and the synthetic white-light radiation, and find a good agreement between simulations and observations. This provides a fundamental background for future simulations to study the triggering and acceleration mechanisms of CMEs under solar wind effects.

Common magnetopause models can predict the location of the magnetopause with respect to upstream conditions from different sets of input parameters, including solar-wind pressure and the interplanetary magnetic field. However, recent studies have shown that some effects of upstream conditions may still be poorly understood since deviations between models and in situ observations beyond the expected scatter due to constant magnetopause motion are quite common. Using data from the three most recent multi-spacecraft missions to near-Earth space (Cluster, THEMIS, and MMS), we investigate the occurrence of these large deviations in observed magnetopause crossings from common empirical models. By comparing the results from different models, we find that the occurrence of these events appears to be model independent, suggesting that some physical processes may be missing from the models. To find these processes, we test whether the deviant magnetopause crossings are statistically associated with foreshocks and/or different solar-wind types and show that, in at least 40 % of cases, the foreshock can be responsible for the large deviations in the magnetopause's location. In the case where the foreshock is unlikely to be responsible, two distinct classes of solar wind are found to occur more frequently in association with the occurrence of magnetopause deviations: the “fast” solar wind and the solar-wind plasma associated with transients such as interplanetary coronal mass ejections. Therefore, the plasma conditions associated with these solar-wind classes could be responsible for the occurrence of deviant magnetopause observations. Our results may help to develop new and more accurate models of the magnetopause, which will be needed, for example, to accurately interpret the results of the upcoming Solar Wind Magnetosphere Ionosphere Link Explorer (SMILE) mission.

Mercury has a large loss cone difference in its two hemispheres due to the northward shifted magnetic dipole. The precipitation difference of energetic electrons in both hemispheres is poorly understood. We show that the northern precipitation is 2.5‐times higher than for a symmetric loss cone due to the effects of the enhanced whistler instability at the southern hemisphere with the larger loss cone. Simulations including nonlinear pitch angle scattering by the whistler‐mode waves show rapid (tens of milliseconds) electron flux modulation related to the wave subpacket structures by repeated interactions within a discrete wave element. The difference in the nonlinear whistler instability in the two hemispheres should enhance the electron precipitation, which, along with the direct impact effects of solar wind, contributes to Mercury's surface–magnetosphere coupling. Electrons hitting the planet's surface may be a possible factor in the formation of water through the formation of hydroxyl groups. Plain Language Summary Mercury, the first planet from the Sun, has north–south asymmetric magnetic fields due to the northward shifted magnetic dipole from the planet's center. Computer simulations of plasma waves and electrons, taking into account Mercury's magnetic dipole offset, show that the northward precipitation of electrons is 2.5‐times higher than in the case of no magnetic dipole offset, which is the case like the Earth. This difference in electron precipitation fraction arises from a difference in the characteristics of wave growth due to the spatial characteristics of the planet's magnetic field, because plasma waves can efficiently push trapped electrons in Mercury's magnetosphere toward the planet's surface. This study contributes to the understanding of the electron precipitation fraction on Mercury and may help to estimate the production of water ice through the formation of hydroxyl groups not only by the direct impact of solar wind but also by the electron precipitation caused by plasma waves. Key Points Whistler‐driven electrons at Mercury are simulated, as the electron precipitation on the planet surface may contribute to water production For an asymmetric (southward wider) loss cone, the northward precipitation fraction is 2.5‐times higher than for a symmetric loss cone Rapid (tens of milliseconds) electron flux modulations can be observed as a signature of repeated interactions with wave subpackets