A statistical study of the properties of large amplitude whistler waves and their association with few eV to 30 keV electron distributions observed in the magnetosphere by Wind

TL;DR

This study statistically analyzes large amplitude whistler waves in Earth's magnetosphere using Wind spacecraft data, revealing their properties, association with energetic electron distributions, and implications for electron energization.

Contribution

It provides the first comprehensive statistical characterization of very large amplitude whistler waves and their correlation with electron distributions in the magnetosphere.

Findings

Approximately 40% of waves exceed 50 mV/m amplitude.

Largest magnetic field amplitude wave recorded at >/- 8 nT.

Associated Poynting flux suggests rapid electron energization.

Abstract

We present a statistical study of the characteristics of very large amplitude whistler waves inside the terrestrial magnetosphere using waveform capture data from the Wind spacecraft as an addition of the study by Kellogg et al., [2010b]. We observed 244(65) whistler waves using electric(magnetic) field data from the Wind spacecraft finding ~40%(~62%) of the waves have peak-to-peak amplitudes of >/- 50 mV/m(>/- 0.5 nT). We present an example waveform capture of the largest magnetic field amplitude (>/- 8 nT peak-to-peak) whistler wave ever reported in the radiation belts. The estimated Poynting flux magnitude associated with this wave is >/- 300 microW/m^2, roughly four orders of magnitude above previous estimates. Such large Poynting flux values are consistent with rapid energization of electrons. The majority of the largest amplitude whistlers occur during magnetically active periods (AE > 200 nT). The waves were observed to exhibit a broad range of propagation angles with respect to the magnetic field, 0{\deg} </- {\theta}_kB < 90{\deg}, which showed no consistent variation with magnetic latitude. These results are inconsistent with the idea that the whistlers are all generated at the equator, propagating along the magnetic field, and that the observed obliqueness is due to propagation effects. We also identified three types of electron distributions observed simultaneously with the whistler waves including beam-like, beam/flattop, and anisotropic distributions. The whistlers exhibited different characteristics depending on the observed electron distributions. The majority of the waveforms observed in our study have f/f_ce </- 0.5 and are observed primarily in the radiation belts simultaneously with anisotropic electron distributions.