Evolution of thermal electron distributions in the magnetotail:
convective heating and scattering-induced losses
Abstract
Earth’s magnetotail is filled with solar wind and ionospheric electrons,
whose initial energies are significantly lower than the typical energies
(temperatures) of plasmasheet electrons. One of the most common
mechanisms responsible for heating of solar wind and ionospheric
electrons in Earth’s magnetotail is adiabatic heating caused by
earthward convection of these electrons from the deep tail (i.e., from
the region of a weak magnetic field) towards the region of stronger
magnetic fields closer to Earth. This heating is moderated by electron
losses into the ionosphere due to local wave scattering. In this study,
we compare electron spectra from simultaneous observations of The Time
History of Events and Macroscale Interactions during Substorms (THEMIS)
spacecraft at different radial distances with spectra obtained from a
simple model that includes adiabatic heating and losses. Our comparison
shows that the model heating significantly overestimates the increase in
energetic (>1 keV) electron fluxes, indicating that losses
are essential for accurate modelling of the observed spectra. The
required electron losses are similar to or even greater than the losses
in the strong diffusion limit (when the loss cone is full). The latter
can be interpreted as loss cone widening by field-aligned electron
acceleration.