The magnetospheric substorm is a key mode of flux and energy transport throughout the magnetosphere associated with distinct and repeatable magnetotail dynamical processes and plasma injections. The substorm growth phase is characterized by current sheet thinning and magnetic field reconfiguration around the equatorial plane. The global characteristics of current sheet thinning are important for understanding of magnetotail state right before the onset of magnetic reconnection and of the key substorm expansion phase. In this paper, we investigate this thinning at different radial distances using plasma sheet (PS) energetic (>50 keV) electrons that reach from the equator to low altitudes during their fast (∼1 s) travel along magnetic field lines. We perform a multi‐case study and a statistical analysis of 34 events with near‐equatorial observations of the current sheet thinning by equatorial missions and concurrent, latitudinal crossings of the ionospheric projection of the magnetotail by the low‐altitude Electron Losses and Fields Investigation (ELFIN) CubeSats at approximately the same local time sector. Energetic electron fluxes thus collected by ELFIN provide near‐instantaneous (<5 min duration) radial snapshots of magnetotail fluxes. Main findings of this study confirm the previously proposed concepts with low‐altitude energetic electron measurements: (a) Energy distributions of low‐altitude fluxes are quantitatively close to the near‐equatorial distributions, which justifies the investigation of the magnetotail current sheet reconfiguration using low‐altitude measurements. (b) The magnetic field reconfiguration during the current sheet thinning (which lasts ≥ an hour) results in a rapid shrinking of the low‐altitude projection of the entire PS (from near‐Earth, ∼10
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.
more » « less- PAR ID:
- 10552716
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Space Weather
- Volume:
- 22
- Issue:
- 10
- ISSN:
- 1542-7390
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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