Brandon Lee Burkholder

The coronal mass ejection (CME) arriving at Earth on 10 May 2024 caused the most intense geomagnetic storm in the last two decades, resulting in highly unusual cusp and magnetopause dynamics. We simulate soft X‐Ray emission due to solar wind charge exchange with exospheric neutrals to image the global dayside dynamics, focusing on the impact of a dense CME current sheet during the storm main phase. The magnetopause moves inward to , and the cusps manifest as nearly parallel emission ridges in X‐Ray. As the interplanetary magnetic field reverses, the cusp ridges move apart to higher latitudes for minutes after the reversal, addressing the open question of how the cusps evolve during and after northward turning of the IMF. Our work highlights soft X‐ray imaging enabling simultaneous observations of extreme solar‐wind impacts across multiple magnetospheric regions.

Along the flank magnetopause, magnetosheath flow interfaced with the relatively stationary magnetosphere produces strong flow shears, and the Kelvin‐Helmholtz instability (KHI) occurs. When the interplanetary magnetic field (IMF) is southward, anti‐parallel day‐side reconnection and KHI can interact, which may enhance the reconnection rate as KHI compresses the current layer and increases the length of the x‐line. If this reconnection transports sufficient magnetic flux into the magnetotail, it may disrupt the magnetotail current sheet. This study examines a Multiscale Atmosphere Geospace Environment (MAGE) simulation of the 10–11 October 2024 geomagnetic storm to quantify the contribution of magnetic flux transported into the magnetotail that is generated where KHI and the anti‐parallel x‐line are co‐located. During a 15‐min interval, the KH unstable dawn flank magnetopause reconnects ∼13% of the flux added to the northern lobe from the subsolar region, or ∼5% of the total magnetospheric open flux.

Along with magnetic reconnection, Kelvin‐Helmholtz (KH) waves are the main mechanisms controlling the solar wind‐magnetosphere interaction, enabling plasma transport into the magnetosphere due to secondary reconnection, diffusion and wave‐particle interactions. In this paper we use global magnetohydrodynamical (MHD) simulations for studying how the Kelvin‐Helmholtz instability (KHI) is modulated by interplanetary magnetic field (IMF) during negative dipole tilt. We find that KH wave activity on the magnetopause maximizes in the winter hemisphere and at dawn sector for positive IMF . These asymmetries of KHI are caused by dawn‐dusk asymmetries of velocity shear on the magnetopause and draped IMF in the magnetosheath. These factors are linked to magnetic reconnection geometry, which also creates a broader boundary layer, slowing the growth of KHI at dusk for positive . These results are important, for example, for understanding field‐aligned currents generated by KH vortices and their ionospheric effects during different seasons and IMF conditions.

A key process in solar‐terrestrial interactions is magnetic reconnection at the magnetopause. In addition to in situ observations of plasma entry at the magnetopause, some of the important global aspects of magnetic reconnection are addressed using plasma observations in the Earth's magnetospheric cusp region. Ions injected at the magnetopause are subject to a time‐of‐flight effect, which results in distinctive ion‐energy dispersions observed in the cusp. The shape of these ion dispersions is analyzed and linked with predictions of the magnetopause reconnection location from the maximum magnetic shear model to determine the plasma entry points at the magnetopause. This study determines how those plasma entry locations affect the observed cusp ion dispersion profiles. This study uses first observations from the Analyzers for Cusp Ions (ACIs) onboard the Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites spacecraft.

The dayside lunar photoelectron sheath generates near-surface electrostatic fields that reflect a fraction of solar wind electrons and accelerate low-energy electrons. As the Moon passes from the solar wind through the magnetosheath and into the magnetotail plasma sheet, electron temperature ( T _e ) and density ( n _e ) can vary by more than 2 orders of magnitude, which leads to large variations of the lunar photoelectron sheath. In order to prepare for a human presence at lunar orbit, this paper quantifies the extremes of T _e and n _e observed by Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun (ARTEMIS) extending over an entire solar cycle. A statistical analysis of ARTEMIS P1 data shows that in solar wind, T _e is in the range 1.6–76 eV and n _e is in the range 0.06–103 cm ⁻³ . In the magnetotail (including magnetosheath, lobe, and plasma sheet), T _e is in the range 6–1800 eV and n _e is in the range 0.03–20 cm ⁻³ (0.03 cm ⁻³ is the instrument threshold, so the lowest density is likely smaller than this). These values were sustained for 1 minute such that the entire moon was immersed in plasma with a particular T _e or n _e . The solar wind T _e and n _e do not have a strong correlation with the solar cycle, but in the magnetotail near midnight, the range of T _e and n _e is significantly larger at solar minimum compared to solar maximum.

On 10 May 2024, Earth was hit by a CME that drove the largest geomagnetic storm in 20 years. Multi‐spacecraft observations previously showed that the ∼100 nT north‐south IMF variation was driven by Kelvin‐Helmholtz waves with wavelength ∼250 and reconnection jets in the ‐direction (Nykyri, 2024a, https://doi.org/10.1029/2024gl110477 ). Here we show that Magnetospheric Multiscale (MMS), located upstream of the Earth's bow shock at , detected additional reconnection jets not seen by ARTEMIS at lunar orbit ∼60 away, perpendicular to CME propagation. One jet coincided with high‐energy ions and electrons streaming anti‐parallel to the magnetic field. The ions showed dispersion followed by apparent counter‐dispersion, whereas electrons above 100 keV arrived nearly simultaneously. Strong electromagnetic wave activity between these phases is consistent with magnetosonic‐Whistler waves, suggesting that MMS traversed very near the particle acceleration region.

We present observations from two consecutive TRACERS‐2 orbits through the northern low‐altitude cusp. During the first crossing, TRACERS‐2 observed reversed cusp ion dispersion and sunward convection, consistent with magnetopause reconnection tailward of the cusp during this northward IMF interval. Simultaneous THEMIS‐D observations at the equatorial magnetopause show heated magnetosheath plasma captured on closed field lines, with similar particle spectra as in the low‐altitude cusp, indicating that reconnection indeed occurred tailward of the cusp and in both hemispheres. When TRACERS‐2 traversed the northern cusp again, 95 min later, the IMF was dominated by a negative B _X component. Despite the different IMF conditions, TRACERS‐2 recorded nearly the same cusp signatures as before, that is, reversed ion dispersion and sunward convection. The observations indicate that tailward‐of‐cusp reconnection can occur for both northward and B _X ‐dominated IMF and that these distinct IMF geometries can produce remarkably similar plasma and field signatures in the low‐altitude cusp.

The Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission observes electron energy‐latitude dispersion at the equatorward edge of the magnetospheric cusp, and high‐cadence Analyzer for Cusp Electrons (ACE) measurements resolve the dispersed edge. The inverse velocity dispersion (low energy before high energy) encountered by TRACERS as it travels southward through the northern cusp rules out pure energy‐time dispersion from nearby injections or Alfvén wave‐driven acceleration. TRACERS observes electron dispersion at the equatorward edge of the northern cusp roughly half of the time for southward interplanetary magnetic field (IMF), and almost never for northward IMF. The TRACERS measurements therefore provide strong observational support for the hypothesis that the observed electron dispersion results from dayside magnetic reconnection and plasma convection, much like the ion dispersion that commonly extends across the cusp. Observations of multiple electron dispersions and electron steps suggest fine‐scale spatial and/or temporal variability in magnetic reconnection.

Magnetopause boundary layers (BLs) play an important role mediating plasma and energy exchange between the solar wind/magnetosheath and Earth's magnetosphere. Energy exchange across the magnetopause is enhanced during storms, yet little work has been done investigating BLs during storms. In this letter, using MMS and THEMIS observations, we investigate the structure and formation of magnetopause BLs during a large coronal mass ejection (CME) driven storm containing 20 hours of low Alfvén Mach number solar wind ( M _A ). Separated by Earth radii (), MMS and THEMIS observe a low latitude boundary layer (LLBL), magnetosheath boundary layer (MSBL), and formation of a plasma depletion layer after a northward interplanetary magnetic field turning. MMS observations indicate lobe reconnection drives the MSBL and LLBL formation. Observations of CME ions on closed field lines demonstrate dual reconnection can trap solar wind plasma under sub‐Alfvenic solar wind conditions and constrain the trapped populations' dwell time.