ELFIN Observations of the Electron Isotropic Boundary at Quiet and Active Times
Abstract
We present a survey of electron Isotropic Boundary (IB) location as a function of energy (50 keV - 5 MeV) at quiet and active times using ELFIN observations. The IB for a given energy is the magnetic latitude of isotropization of precipitating and trapped particle fluxes, interpreted as due to magnetic curvature scattering at the equator. It characterizes the radial transition of the near-Earth magnetic field from a dipole-like to a tail-like (stretched) configuration, capable of non-adiabatic curvature scattering of electrons with gyroradii comparable to the scale of field line curvature. Knowledge of the instantaneous IB layer location is an important remote measure of the magnetic field curvature profile in the tail, and of great value to refinement of magnetic field models connecting the ionosphere to the nightside magnetosphere under varying geomagnetic activity and substorm phases. The set of electron IB locations as a function of energy are obtained by the ELFIN dual 3U CubeSat mission, which launched in 2018 to study the loss of energetic electrons in the inner magnetosphere. The ELFIN satellites are presently in a 450 km circular polar orbit and are equipped with state-of-the-art energetic particle detectors (EPDs) to measure differential electron fluxes from 50 keV to ~5 MeV with high energy resolution (dE/E<0.4) in 16 channels and 16 pitch-angle bins (11.5 deg resolution at 2-3 secs/spin). The high-resolution electron observations provide a unique opportunity to determine the fine energy structure of the isotropic boundary over a wide range of L-shells with frequent transits. Additionally, because the two ELFIN spacecraft are in the same orbit track but delayed in time (by minutes up to ~1 hr), they provide a unique opportunity to also quantify the short-term variability of the IB layer location as it evolves during periods of activity. Possibilities for a secondary IB layer resulting from the potential of multiple tail Bz extrema (non-monotonic with respect to tailward distance) are also explored.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSM023..03W
- Keywords:
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- 2455 Particle precipitation;
- IONOSPHERE;
- 2716 Energetic particles: precipitating;
- MAGNETOSPHERIC PHYSICS;
- 7867 Wave/particle interactions;
- SPACE PLASMA PHYSICS;
- 7999 General or miscellaneous;
- SPACE WEATHER