Picturing Global Substorm Dynamics in the Magnetotail Using Low‐Altitude ELFIN Measurements and Data Mining‐Based Magnetic Field Reconstructions

A global reconfiguration of the magnetotail characterizes substorms. Current sheet thinning, intensification, and magnetic field stretching are defining features of the substorm growth phase and their spatial distributions control the timing and location of substorm onset. Presently, sparse in‐situ observations cannot resolve these distributions. A promising approach is to use new substorm magnetic field reconstruction methods based on data mining, termed SST19. Here we compare the SST19 reconstructions to low‐altitude electron losses and fields investigation (ELFIN) measurements of energetic particle precipitations to probe the radial profile of the equatorial magnetic field curvature during a 19 August 2022 substorm. ELFIN and SST19 yield a consistent dynamical picture of the magnetotail during the growth phase and capture its key features such as the formation of a thin current sheet and its earthward motion. Furthermore, they resolve a “checkmark” pattern of isotropic electron precipitation boundaries in the time‐energy plane, consistent with earlier observations but now over a broad energy range. It is shown that in the growth phase, the mismatch between SST19 and ELFIN latitudes is much less than one degree, the capability unattainable for any other empirical or first‐principles model.