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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 NASA Radiation Belt Storm Probes (RBSP) mission addresses how populations of high energy charged particles are created, vary, and evolve in space environments, and specifically within Earth’s magnetically trapped radiation belts. RBSP, with a nominal launch date of August 2012, comprises two spacecraft making in situ measurements for at least 2 years in nearly the same highly elliptical, low inclination orbits (1.1×5.8 RE, 10 ∘ ). The orbits are slightly different so that 1 spacecraft laps the other spacecraft about every 2.5 months, allowing separation of spatial from temporal effects over spatial scales ranging from ∼0.1 to 5 RE. The uniquely comprehensive suite of instruments, identical on the two spacecraft, measures all of the particle (electrons, ions, ion composition), fields ( E and B ), and wave distributions ( d E and d B ) that are needed to resolve the most critical science questions. Here we summarize the high level science objectives for the RBSP mission, provide historical background on studies of Earth and planetary radiation belts, present examples of the most compelling scientific mysteries of the radiation belts, present the mission design of the RBSP mission that targets these mysteries and objectives, present the observation and measurement requirements for the mission, and introduce the instrumentation that will deliver these measurements. This paper references and is followed by a number of companion papers that describe the details of the RBSP mission, spacecraft, and instruments.

A global magnetohydrodynamic model predicts the response of the magnetosphere to the passage of a foreshock transient. We simulate the transient as an antisunward‐ and dawnward‐moving slab of hot tenuous solar wind plasma and weak magnetic field strengths on magnetic field lines connected to the bow shock. The slab elicits large‐amplitude outward bow shock motion with a stronger jump in plasma and magnetic field parameters on the trailing than the leading edges of this motion. The outward bulge in the bow shock bounds a magnetosheath region containing a hot tenuous plasma with weakened magnetic field strengths and flows deflected away from the Sun‐earth line. The magnetopause bulges outward into this magnetosheath region to distances beyond the nominal bow shock. Despite the large amplitude magnetopause motion, perturbations at geosynchronous orbit are miniscule. Model predictions compare well to the observed characteristics of foreshock transients and their effects on the magnetosphere. Plain Language Summary The arrival of a dawnward or duskward‐moving slab of very hot and tenuous solar wind plasma creates large amplitude but localized outward bulges in the bow shock wave that stands upstream from the Earth's magnetosphere. The magnetopause, or outermost boundary of the magnetospheric magnetic field, protrudes several Earth radii outward to fill the cavity created by these bulges. Both the bow shock bulge and the magnetopause protrusion move dawnward or duskward with the slab along the locus of points connecting it to the bow shock. Despite the large amplitude bow shock and magnetopause motion, the passage of a slab produces only modest signatures at dayside geosynchronous orbit. Key Points A global magnetohydrodynamic model simulates the interaction of a low density slab of solar wind plasma and weak radial magnetic fields with the bow shock The interaction generates a hot tenuous transient foreshock event with weak magnetic fields bounded by shocks A large amplitude wave on the magnetopause that extends far upstream into this transient event elicits no strong geosynchronous signature

The Lunar Environment heliospheric X-ray Imager (LEXI) is a wide field-of-view soft Xray telescope developed to study solar wind-magnetosphere coupling. LEXI is part of the Blue Ghost 1 mission comprised of 10 payloads to be deployed on the lunar surface. LEXI monitors the dayside magnetopause position and shape as a function of time by observing soft X-rays (0.1–2 keV) emitted from solar wind charge-exchange between exospheric neutrals and high charge-state solar wind plasma in the dayside magnetosheath. Measurements of the shape and position of the magnetopause are used to test temporal models of mesoand macro-scale magnetic reconnection. To image the boundary, LEXI employs lobster-eye optics to focus X-rays to a microchannel plate detector with a 9.1◦ × 9.1◦ field of view.

Magnetic reconnection is the primary process through which energy couples from the solar wind into Earth's magnetosphere and ionosphere. Conditions both in the incident solar wind and in the magnetosphere are important in determining the efficiency of this energy transfer. In particular, the cold, dense plasmaspheric plume can substantially impact the coupling in the dayside reconnection region. Using ground-based total electron content (TEC) maps and measurements from the THEMIS spacecraft, we investigated simultaneous ionosphere and magnetosphere observations of the plasmaspheric plume and its involvement in an unsteady magnetic reconnection process. The observations show the full circulation pattern of the plasmaspheric plume and validate the connection between signatures of variability in the dense plume and reconnection at the magnetopause as measured in situ and through TEC measurements in the ionosphere.

We employ 2.5‐D electromagnetic, hybrid simulations that treat ions kinetically via particle‐in‐cell methods and electrons as a massless fluid to study the formation and properties of a new structure named the foreshock bubble upstream from the bow shock. This structure forms due to changes in the interplanetary magnetic field (IMF) associated with solar wind discontinuities and their interaction with the backstreaming ions in the foreshock prior to these discontinuities encountering the bow shock. The leading edge of the foreshock bubble consists of a fast magnetosonic shock and the compressed and heated plasma downstream of the shock. The leading edge surrounds the core which consists of a less‐dense and hotter plasma and lower magnetic field strength. Ultra low frequency turbulence is present in both the outer and core regions of the foreshock bubbles. The size of the foreshock bubble transverse to the flow direction scales with the width of the ion foreshock and at Earth corresponds to tens of RE. The size along the flow depends on the age of the bubble and grows with time. Although they expand sunward, foreshock bubbles are carried antisunward by the solar wind, and for small IMF cone angles (angle between IMF and solar wind flow) when the foreshock lies upstream of the dayside magnetosphere they collide with the bow shock. This collision is shown to have significant magnetospheric impacts. Upon encountering the bow shock, the low pressures within the core of the bubble result in the reversal of the magnetosheath flow from antisunward to sunward direction. This in turn results in the outward motion of the magnetopause and expansion of the dayside magnetosphere. The interaction is found to noticeably impact the density and energy of trapped radiation belt ions and plasma injection into the cusp. Foreshock bubbles are found to be highly effective sites for ion reflection and acceleration to high energies via first‐ and second‐order Fermi acceleration. The interaction of the foreshock bubble with the bow shock results in the release of energetic ions into the magnetosheath. Some of these ions are subsequently injected into the cusp.

The typical subsolar stand‐off distance of Mars' bow shock is of the order of a solar wind ion convective gyroradius, making it highly non‐planar to incident ions. Using spacecraft observations and a test particle model, we illustrate the impact of the bow shock curvature on transient structures which form near the upstream edge of moving foreshocks caused by slow rotations in the interplanetary magnetic field (IMF). The structures exhibit noticeable decrease in the solar wind plasma density and the IMF strength within their core, are accompanied by a compressional shock layer, and are consistent with foreshock bubbles (FBs). Ion populations responsible for these structures include backstreaming ions that only appear within the moving foreshock and reflected ions with hybrid trajectories that straddle between the quasi‐perpendicular and quasi‐parallel bow shocks during slow IMF rotations. Both ion populations accumulate near the upstream edge of the moving foreshock which facilitates FB formation. Plain Language Summary Planets in the solar system are continuously impacted by the solar wind, a plasma flow originating at the Sun and propagating through the interplanetary medium at high speeds. The solar wind also carries a magnetic field which at times contains twists or discontinuities. The discontinuities are associated with large scale electric currents that can have planar shapes. A planetary obstacle significantly modulate the solar wind plasma and the interaction of solar wind discontinuities with the modulated plasma upstream of the planet leads to formation of transient structures. Due to their relatively large size, these structures can significantly impact and destabilize plasma boundaries at lower altitudes closer to the surface. The results of this paper improve our understanding of solar wind interactions and formation of transient structures upstream of Mars. Key Points Foreshock bubbles can form upstream of Mars Slow field rotations can cause foreshock bubbles while reflected ions from the quasi‐perpendicular bow shock contribute to their formation Unique ion kinetic scale processes exist around foreshock structures at Mars due to the different interaction size scale

Statistical observations by the THEMIS spacecraft show a dawn‐dusk asymmetry in plasma parameters within the Earth's magnetosheath. Proton density and temperature are greater on the dawnside while the magnetic field strength and bulk flow are greater on the duskside. The asymmetry has been measured just outside the magnetopause in the dayside magnetosheath through 1114 boundary crossings from 2008 through 2010. These results are compared with modeling from the BATS‐R‐US global MHD code and are consistent with the expected asymmetries that would result from the interactions of the Parker spiral interplanetary magnetic field with the Earth's bow shock. Solar cycle variations are analyzed for the current and past studies to predict the influence of upstream conditions during different time periods. Key Points A dawn‐dusk magentosheath asymmetry exists for B, n, T, and V Modeling suggests the magnetosheath asymmetry is the result of the Parker spiral

We report the first in situ observation of high‐latitude magnetopause (near the northern duskward cusp) Kelvin‐Helmholtz waves (KHW) by Cluster on January 12, 2003, under strongly dawnward interplanetary magnetic field (IMF) conditions. The fluctuations unstable to Kelvin‐Helmholtz instability (KHI) are found to propagate mostly tailward, i.e., along the direction almost 90° to both the magnetosheath and geomagnetic fields, which lowers the threshold of the KHI. The magnetic configuration across the boundary layer near the northern duskward cusp region during dawnward IMF is similar to that in the low‐latitude boundary layer under northward IMF, in that (1) both magnetosheath and magnetospheric fields across the local boundary layer constitute the lowest magnetic shear and (2) the tailward propagation of the KHW is perpendicular to both fields. Approximately 3‐hour‐long periods of the KHW during dawnward IMF are followed by the rapid expansion of the dayside magnetosphere associated with the passage of an IMF discontinuity that characterizes an abrupt change in IMF cone angle,ϕ = acos BxB , from ∼90° to ∼10°. Cluster, which was on its outbound trajectory, continued observing the boundary waves at the northern evening‐side magnetopause during sunward IMF conditions following the passage of the IMF discontinuity. By comparing the signatures of boundary fluctuations before and after the IMF discontinuity, we report that the frequencies of the most unstable KH modes increased after the discontinuity passed. This result demonstrates that differences in IMF orientations (especially inϕ) are associated with the properties of KHW at the high‐latitude magnetopause due to variations in thickness of the boundary layer, and/or width of the KH‐unstable band on the surface of the dayside magnetopause. Key Points First in situ observation of Kelvin‐Helmholtz wave at high‐latitude magnetopause The effect of the IMF cone angle on the generation of KH waves The effect of a boundary thickness and magnetic shear on properties of KH waves