Substantial Equatorward Auroral Expansion Driven by Deep Penetration of Magnetospheric Convection During the May 2024 Superstorm

Abstract During extreme geomagnetic storms, the auroral oval can move equatorward beyond its typical high‐latitude location, producing low‐latitude auroras, yet the physical process controlling such substantial expansion remains unresolved. Using coordinated space and ground‐based observations, we investigate the equatorward expansion of the auroral oval in the postmidnight‐to‐dawn sector during the main phase of the May 2024 superstorm. The equatorward boundary of the auroral oval is observed to extend below 50 magnetic latitude. We show that this substantial expansion results from the deep earthward penetration of magnetospheric convection. Enhanced solar‐wind‐driven convection transported plasma sheet particles earthward, bringing electron precipitation at lower latitudes and producing a coherent equatorward displacement of the auroral oval. Consistent with this expansion, Region 1/2 field‐aligned currents and auroral electrojets also shifted to lower latitudes. These observations identify magnetospheric convection penetration as a key process controlling substantial low‐latitude auroral expansion. Given the stronger, more deeply penetrating convection expected at higher Kp and more negative Dst, this mechanism may also help explain the substantial equatorward auroral expansion observed during previous superstorms.