The Day-Side Magnetic Reconnection Rate and Cusp Ion Dispersion During the May 2024 Geomagnetic Storm

During intense space weather events, magnetic flux can be rapidly eroded from the Earth's day-side magnetosphere, potentially exposing satellites as low as geosynchronous orbit (∼5.6 (Formula presented.) altitude) directly to magnetosheath plasma. This was observed during the 10–11 May 2024 geomagnetic storm, the most severe storm to have occurred in over two decades. High interplanetary magnetic field (IMF) strength and solar wind dynamic pressure within multiple interacting coronal mass ejections resulted in strongly driven magnetic reconnection at the day-side magnetopause. A Multiscale Atmosphere Geospace Environment (MAGE) simulation of the May 2024 geomagnetic storm shows the day-side magnetopause reconnection rate reached (Formula presented.) mV/m during two different intervals of storm-time southward IMF, a factor of at least 5 larger than quiet time. One of the selected intervals also has a significant (Formula presented.) component of the IMF, which leads to a large component x-line on the day-side magnetopause. Super Dual Auroral Radar Network radar observations during the nonzero (Formula presented.) interval infer reconnection rates up to 5 mV/m, consistent with the simulation. Simulated cusp ion test particle dispersions estimate reconnection rates of (Formula presented.) mV/m during the zero (Formula presented.) interval and (Formula presented.) mV/m during the nonzero (Formula presented.) interval.