  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 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 expected features such as the formation of a thin
current sheet and its earthward motion. Furthermore, they resolve a V-like
pattern of isotropic electron precipitation boundaries in the time-energy
plane, consistent with earlier observations but now over a broad energy range.
