D. Sibeck | Searcharxiv

arXiv2025

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

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

physics.space-ph↗

arXiv2013

Active current sheets and hot flow anomalies in Mercury's bow shock

Hot flow anomalies (HFAs) represent a subset of solar wind discontinuities interacting with collisionless bow shocks. They are typically formed when the normal component of motional (convective) electric field points toward the embedded current sheet on at least one of its sides. The core region of an HFA contains hot and highly deflected ion flows and rather low and turbulent magnetic field. In this paper, we report first observations of HFA-like events at Mercury identified over a course of two planetary years. Using data from the orbital phase of the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission, we identify a representative ensemble of active current sheets magnetically connected to Mercury's bow shock. We show that some of these events exhibit unambiguous magnetic and particle signatures of HFAs similar to those observed earlier at other planets, and present their key physical characteristics. Our analysis suggests that Mercury's bow shock does not only mediate the flow of supersonic solar wind plasma but also provides conditions for local particle acceleration and heating as predicted by previous numerical simulations. Together with earlier observations of HFA activity at Earth, Venus and Saturn, our results confirm that hot flow anomalies are a common property of planetary bow shocks, and show that the characteristic size of these events is of the order of one planetary radius.

astro-ph.EP↗