Bibliography

Low Frequency ULF Waves in the Earth’s Inner Magnetosphere: Statistics During Coronal Mass Ejections and Seeding of EMIC Waves

Abstract Here we perform a statistical analysis of low frequency ultra-low-frequency (ULF) waves (mHz-Hz) in the Earth’s inner magnetosphere excluding electromagnetic ion cyclotron (EMIC) waves concurrently observed. We use the magnetic field data from the two Van Allen Probes during their first magnetic local time (MLT) revolution that cover the periods of coronal mass ejections. The major results of our analysis are as follows. (1) Spectra of both the transverse and compressional ULF waves are well approximated by the power-laws in the mHz-Hz frequency range. (2) There are two sources of the low frequency ULF waves: an internal magnetospheric source and an external source outside of the magnetosphere. (3) The average transverse power in the 6-24 hr MLT sector dominates that in the 0-6 hr sector, whereas the compressional power in the 12-24 hr sector dominates that in the 0-12 hr sector. (4) The average powers of transverse and compressional ULF waves in the plasmasphere dominate the average powers in the high L shell region of , and there is a deep power minimum in the intermediary region of . (5) The compressional ULF wave power has a maximum in the near equatorial region, whereas the transverse power has a minimum there. (6) A wave energy cascade from low frequency ULF waves into the higher frequency range of EMIC waves (Hz) supplies the nonthermal seed fluctuations from which EMIC waves can then grow due to instabilities of the energetic magnetospheric ions. This article is protected by copyright. All rights reserved.

Gamayunov, Konstantin; Engebretson, Mark;

Published by: Journal of Geophysical Research: Space Physics      Published on: 07/2021

YEAR: 2021     DOI: https://doi.org/10.1029/2021JA029247

coronal mass ejection; low frequency ULF waves; Earth s inner magnetosphere; statistics of ULF waves; turbulent energy cascade; seeding of EMIC waves; Van Allen Probes

Equatorial pitch angle distributions of 1 – 50 keV electrons in Earth s inner magnetosphere: an empirical model based on the Van Allen Probes observations

Using seven years of data from the HOPE instrument on the Van Allen Probes, equatorial pitch angle distributions (PADs) of 1 – 50 keV electrons in Earth s inner magnetosphere are investigated statistically. An empirical model of electron equatorial PADs as a function of radial distance, magnetic local time, geomagnetic activity, and electron energy is constructed using the method of Legendre polynomial fitting. Model results show that most equatorial PADs of 1 – 10s of keV electrons in Earth s inner magnetosphere are pancake PADs, and the lack of butterfly PADs is likely due to their relatively flat or positive flux radial gradients at higher altitudes. During geomagnetically quiet times, more anisotropic distributions of 1 – 10s of keV electrons at dayside than nightside are observed, which could be responsible for moderate chorus wave activities at dayside during quiet times as reported by previous studies. During active times, the anisotropy of 1 – 10s of keV electrons significantly enhances, consistent with the enhanced chorus wave activity during active times and suggesting the critical role of 1 – 10s of keV electrons in generating chorus waves in Earth s inner magnetosphere. Different enhanced anisotropy patterns of different energy electrons are also observed during active times: at R>∼4 RE, keV electrons are more anisotropic at dawn to noon, while 10s of keV electrons have larger anisotropy at midnight to dawn. These differences, combined with the statistical distribution of chorus waves shown in previous studies, suggest the differential roles of electrons with different energies in generating chorus waves with different properties. This article is protected by copyright. All rights reserved.

Zhao, H.; Friedel, R.; Chen, Y.; Baker, D.; Li, X.; Malaspina, D.; Larsen, B.; Skoug, R.; Funsten, H.; Reeves, G.; Boyd, A.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2020

YEAR: 2020     DOI: https://doi.org/10.1029/2020JA028322

Pitch angle distribution; energetic electrons; Earth s inner magnetosphere; Anisotropy; Chorus wave; statistical analysis; Van Allen Probes