Time of flight analysis of pulsating aurora electrons, considering wave‐particle interactions with propagating whistler mode waves

Abstract

[1] We propose a model for the energy dispersion of electron precipitation associated with pulsating auroras, considering the wave-particle interactions with propagating whistler mode waves from the equator. Since the resonant energy depends on the magnetic latitude, the pitch angle scattering of different energy electrons can occur continuously along the field line. Considering the energy-dependent path length and the precipitation start time of the precipitating electrons, the transit time of whistler mode waves, and the frequency drift, we calculated the precipitation of electrons observed at the topside ionosphere. Note that higher energy electrons precipitate into the ionosphere of the opposite hemisphere earlier than lower energy electrons. As a result, an energy dispersion of precipitating electrons is observed at the topside ionosphere, even though the modulation of low energy electrons occurs prior to that of high energy electrons. Using the model, we conducted a time-of-flight (TOF) analysis of precipitating electrons observed by the REIMEI satellite, assuming an interaction with the whistler mode chorus rising tone. Our TOF analysis suggests that the modulation region of the pitch angle scattering is near the magnetic equator, whereas previous models expected that the modulation region is far from the magnetic equator. The estimated parameters, such as wave-frequency and latitudinal distribution of the modulation region, are consistent with previous statistical studies of whistler waves at the magnetosphere.

Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution

“…Pulses with a slower rise time appeared as a few consecutive pulses, and the pulses with a slower fall time appeared for at most two pulsations at a time. The slow rise time is unlikely to be due to time-offlight effects of electrons of varying energy since the rise time is much longer than realistic dispersion times, as observed with Reimei and modelled by Miyoshi et al (2010), and also since the pulses of slower rise time are not seen for the majority of the pulses, which would then be the case. also found auroral pulsations where the rise time was slower than the fall time.…”

“…The most accepted the-ory is that high-energy electrons in the central plasma sheet get pitch angle scattered into the loss cone by cyclotron resonance with very-low-frequency (VLF) plasma waves (Coroniti and Kennel, 1970;Johnstone, 1983;Davidson, 1990). Time-of-flight analysis of the energy dispersion of the precipitating electrons as measured by the Reimei satellite showed that the source region of the scattered electrons is near the magnetic equator (Miyoshi et al, 2010). There are two main wave modes that can resonate with plasma sheet electrons in the equatorial plane in the energy ranges observed for pulsating aurora: electrostatic electron cyclotron harmonic (ECH) waves, which will interact with plasma sheet electrons of energies ranging from a few hundred electron volts to a few kilo-electronvolts, and electromagnetic whistlermode chorus waves, which can resonate with electrons of a few to several tens of kilo-electronvolts (Horne et al, 2003;Meredith et al, 2009).…”

Low‐altitude satellite measurements of pulsating auroral electrons

“…However, other rocket observations have measured Maxwellian characteristic energies of 10 keV to 12 keV [Johnstone, 1978;Smith et al, 1980], andMcEwan et al [1981] reported energies as low as 1 keV to 2 keV. More recently, Jaynes et al [2013] reported energies ranging from 30 keV to 50 keV, and Reimei satellite observations have revealed pulsating aurora associated with 8 keV to 12 keV electron precipitation using ground-based imaging and the onboard imager on Reimei [Miyoshi et al, 2010]. Stenbaek-Nielsen and Hallinan [1979], using triangulation and assuming typical atmospheric parameters, determined the altitude of many pulsating aurora events to be 10.1002/2015JA021292 below 92 km, indicating a Maxwellian characteristic energy of the incident primary electron beam in excess of 20 keV.…”

Ground‐based ELF/VLF chorus observations at subauroral latitudes—VLF‐CHAIN Campaign

“…These waves interact with high-energy (10-100 keV) electrons and cause modulation of spectacular pulsating auroras [e.g., Tsuruda et al, 1981;Nishimura et al, 2010;Miyoshi et al, 2010;Lessard, 2012;Li et al, 2012;Ozaki et al, 2012]. ELF/VLF chorus emissions can also interact with relativistic electrons in the radiation belts, contributing to their acceleration and dissipation in the inner magnetosphere [e.g., Miyoshi et al, 2003Miyoshi et al, , 2007Katoh and Omura, 2007;Kasahara et al, 2009].…”