Temporal Scales of Electron Precipitation Driven by Whistler-Mode Waves

TL;DR

This study uses ELFIN CubeSat measurements to analyze the temporal and spatial scales of electron precipitation driven by whistler-mode waves, revealing how different scales influence electron loss in Earth's outer radiation belt.

Contribution

It provides a detailed characterization of the temporal and spatial scales of electron precipitation variations caused by whistler-mode waves using multi-satellite data.

Findings

Small-scale variations (0.1-1 s, 100 km) linked to chorus wave packets.

Intermediate-scale variations (a few seconds to minutes, 1000 km) associated with ULF wave modulations.

Large-scale variations (several minutes to over 10 min, 1000-10000 km) related to mesoscale plasma structures.

Abstract

Electron resonant scattering by whistler-mode waves is one of the most important mechanisms responsible for electron precipitation to the Earth's atmosphere. We investigate temporal and spatial scales of such precipitation with measurements from the two low-altitude ELFIN CubeSats. We compare the variations in energetic electron precipitation at the same L-shells but on successive data collection orbit tracks by the two ELFIN satellites. Variations seen at the smallest inter-satellite separations are likely associated with whistler-mode chorus elements or with the scale of chorus wave packets (0.1 - 1 s in time and 100 km in space at the equator). Variations between precipitation L-shell profiles at intermediate inter-satellite separations are likely associated with whistler-mode wave power modulations by ultra-low frequency (ULF) waves, i.e., with the wave source region (from a few to tens of seconds to a few minutes in time and 1000km in space at the equator). During these two types of variations, consecutive crossings are associated with precipitation L-shell profiles very similar to each other. Therefore the spatial and temporal variations at those scales do not change the net electron loss from the outer radiation belt. Variations at the largest range of inter-satellite separations, several minutes to more than 10 min, are likely associated with mesoscale equatorial plasma structures that are affected by convection (at minutes to tens of minutes temporal variations and [1000,10000]km spatial scales). The latter type of variations results in appreciable changes in the precipitation L-shell profiles and can significantly modify the net electron losses during successive tracks.