Predictive radar tracking reveals >500 mV/m electric-field transients during the May 2024 superstorm

arXiv:2605.31046v2 Announce Type: replace Abstract: The bulk motion of E-region radar aurora provides a sparsely distributed, direct measurement of the ionospheric electric field in intermittent bursts. We present a tracking procedure for \textsc{icebear} VHF measurements of Farley-Buneman waves. Each cluster is represented as an $\alpha$-shape; frame-to-frame association is a Hungarian linear-assignment problem with a cost combining centroid distance and shape Intersection-over-Union; kinematic prediction amounts to a degenerate Kalman filter. Births, deaths, splits, and mergers are monitored; each tracked trajectory is reduced to per-segment velocities by piecewise-linear regression. We validate against \textit{in-situ} observations. During the G5 storm of 10 May 2024, on closed dayside field-lines, our method recovers a five-second cluster moving at $11{,}240\pm660$~m/s, implying an electric field strength of $\approx 560$~mV/m, a value that exceeds documented sub-auroral thermal emission speeds and the most extreme reported sub-auroral drifts. The detection is consistent with extreme E-field structures appearing as short-lived bursts, representing field variability, and we provide parameterizations of this variability for space weather modeling.