Statistical distributions of field‐aligned electron events in the near‐equatorial magnetosphere observed by the Low Energy Plasma Analyzer on CRRES

Abstract

Low energy (≤100 eV–10 keV) field‐aligned electrons are often observed by the Low Energy Plasma Analyzer (LEPA) on the CRRES satellite. These electrons usually occur in bursts of <10 min duration and are mostly bidirectional, though opposing fluxes are not always equal. The events can be seen from L‐values of 5 outward (to at least L = 7) and from 0800 magnetic local time (MLT) through midnight to 1400 MLT. Larger numbers of events were seen at the outer edge of CRRES' coverage and in the evening and early morning sectors, when the apogee of CRRES was at higher latitudes. The bursts normally occur within 20 min of substorm onset. High‐latitude, low‐altitude spacecraft often observe upgoing field‐aligned electron beams. We suggest that these are the source of the field‐aligned electron beams seen by CRRES near the equator.

Quasi-parallel electron beams and their possible application in inferring the auroral arc's root in the magnetosphere

“…For example, the energy range (∼ 100-500 eV), the peak energy flux level (∼ 10 8 eV cm −2 s −1 sr −1 eV −1 ), and the beam width (< 20 • ) of our observed QPEBs are all compatible with the results from a statistical survey by Abel et al (2002b) based upon CRRES measurements in the nightside inner magnetosphere. However, before we claim that those QPEBs are the magnetospheric trace of the upgoing electron beams from the ionosphere, we need to carefully examine other candidate mechanisms capable of producing electrons with parallel/antiparallel anisotropy.…”

“…The electron beams then become largely a "trapped" population that bounce within the magnetosphere. Eventually, the electron beams appear on magnetosphere satellite measurements as collimated beams with finite beam width (∼ 10-15 • in the nightside inner magnetosphere as surveyed by Abel et al, 2002b) along directions both parallel and antiparallel to the ambient magnetic field. Such bidirectional, collimated electron beams were previously reported on the basis of data from magnetospheric satellites such as ATS-6 (Lin et al, 1979), AMPTE/CCE (Klumpar et al, 1988;Klumpar;1993), CRRES (Abel et al, 2002a, b), and Cluster (Marklund et al, 2004;Wright et al, 2008).…”

Oblique Whistler-Mode Waves in the Earth’s Inner Magnetosphere: Energy Distribution, Origins, and Role in Radiation Belt Dynamics

“…47 Profiles of growth/damping rate for whistler-mode waves (with ω pe /Ω ce = 4.5) in the presence of a weak temperature anisotropy A e = T ⊥ /T and with a negligible Landau damping from suprathermal electrons following substorm onset dipolarizations (Abel et al 2002). Further comparisons with the required resonant parallel energy for wave-particle interaction indicate that such very low energy sporadic beams should probably excite very oblique lower-band waves mainly via Landau resonance (Mourenas et al 2015).…”

Fast earthward flows, electron cyclotron harmonic waves, and diffuse auroras: Conjunctive observations and a synthesized scenario

“…This feature cannot be attributed to an injection from remote substorm origin since the required drift time for ∼100 eV electrons would have been much too long. We have also carefully examined the pitch angle distribution (not shown) of this soft electron flux enhancement in full‐angular‐resolution measurements, and found it is unlikely to be composed of field‐aligned electron beam of ionospheric origin either [e.g., Abel et al , 2002]. One reasonable interpretation to such soft electron flux enhancement is that it was contributed by the “cold” electrons carried by the fast flows from the mid‐tail.…”