The May 2024 Storm: dayside magnetopause and cusps in simulated soft X-Rays

TL;DR

This study addresses how a dense CME current sheet during the May 2024 storm restructures Earth's dayside magnetopause and cusps, using synthetic soft X-ray images derived from a MAGE-based global geospace model. A soft X-ray production model is coupled with a global simulation to generate images via a line-of-sight integration of solar wind–geocoronal charge-exchange emissions, focusing on a dense IMF reversal. Key findings show the magnetopause compressing inward to about $4\,R_E$ during the CME arrival, with two cusp emission ridges forming and migrating poleward after the IMF $B_z$ turns northward, the northern cusp remaining brighter due to sunward dipole tilt and solar wind flow. The results demonstrate the potential of global X-ray imaging (e.g., STORM/SMILE) to provide quantitative, large-scale measurements of magnetopause and cusp locations and dynamics under extreme solar wind conditions, complementing in situ and ionospheric observations.

Abstract

The coronal mass ejection (CME) arriving at Earth on May 10, 2024 caused the most intense geomagnetic storm in the last two decades, and resulted in highly unusual magnetopause and cusp 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 ~ 4 RE, and at the same time, the two cusps manifest as nearly parallel emission ridges in X-Ray. As the interplanetary magnetic field reverses, the cusp ridges move to higher latitudes for ~ 10 minutes after the reversal. The X-Ray emission can be detected by imagers to be flown on future missions to provide a global picture of the magnetopause and cusps with quantitative determination of their locations

Figures (3)

• Figure 1: Upstream magnetic field (B), density (n), velocity(V) and temperature (T) used as the simulation input. The data were measured by MMS (B, n, V) and Wind (T), and all data have been time-shifted to the bow shock nose. The reversal of the magnetic field $B_y$ and $B_z$ is associated with a density pulse reaching 120 $cm^{-3}$ and a temperature drop immediately after the density pulse.
• Figure 2: (Top) Volume rendering of the integrand of Equation \ref{['eq:xray']} at 22:36 UT. The white sphere and yellow line show a line-of-sight from a spacecraft positioned at $y=30 R_E$ ($x=z=0$). IMF field lines are drawn in cyan. Red and green field lines connect to the southern and northern cusps respectively. Magenta field lines are closed. (Bottom) Soft X-ray intensity after line of sight integration observed by an imager at [0, 30, 0] $R_E$ (top row) and at [0, 0, 30] $R_E$ (bottom row) . The soft X-ray images are constructed with an angular resolution $0.25^\circ \times 0.25^\circ$. The STORM mission is designed to have an angular resolution $0.17^\circ$ to $0.25^\circ$ and a field of view marked by the boxes. Annotations show Northern cusp (NC), Southern cusp (SC) and magnetopause (MP). All vectors are in the SM coordinates.
• Figure 3: [Left] Magnetopause position determined by magnetic topology (top panel) and extrema in the X-ray intensity and its second derivative (bottom). [Right] X-ray intensity as seen from $y = 30 R_E$ along $\theta_2 = 0$ showing the motion of the magnetopause.