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Whistler-Mode Waves in Near-Equatorial THEMIS Measurements: Reconstruction of Magnetic Field Spectra From Electric Field and Plasma Measurements
Journal article   Peer reviewed

Whistler-Mode Waves in Near-Equatorial THEMIS Measurements: Reconstruction of Magnetic Field Spectra From Electric Field and Plasma Measurements

Declan Frawley, Dmitri L. Vainchtein, Anton V. Artemyev and Vassilis Angelopoulos
Journal of geophysical research : Space physics (2013 - Present), v 131(6), 2026
06 Jun 2026
DOI: https://doi.org/10.1029/2026JA035333

Abstract

Astronomy & Astrophysics Science & Technology Physical Sciences
Electromagnetic whistler-mode waves are a natural emission in the outer radiation belt and the Earth's magnetotail. The resonant interaction of these waves and energetic electrons are responsible for electron acceleration and losses, thus coupling the magnetosphere and ionosphere. Near-equatorial spacecraft use search-coil magnetometers for whistler-mode wave measurements, and one of the largest (covering the longest period of time) data set of such waves has been collected by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission operating in the near-Earth magnetosphere within 2008-2025. However, after 2017, the search-coil magnetometers on two THEMIS spacecraft, THEMIS E and D, experienced problems with their signal in the plane normal to the spacecraft spin axis and were only able to detect the spin plane components of the wave vector. This significantly reduces our ability to detect the total wave amplitude and limits our ability to incorporate the THEMIS E, D data sets into investigation of whistler-mode waves. In this technical report, we propose and validate a technique for the reconstruction of magnetic field spectral density for Fast Fourier transform data product collected during Fast-Survey mode hereafter referred to as the fff data set collected by THEMIS E and D. We use measurements of the electric field instrument and cold plasma dispersion relation to evaluate the whistler-mode magnetic field spectral density. Verification of this technique by comparison with THEMIS A measurements (which retained their 3D measurement capability intact) confirms that restored magnetic field spectral density is within a factor of & times;1.5 of the actually measured magnitudes.

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