Plots recording observations of electromagnetic ion cyclotron waves at four different locations
(a) Frequency spectrogram of the observed electromagnetic ion cyclotron (EMIC) wave (north-south magnetic field component) at Eskdalemuir, Scotland (ESK) at the same time as the satellite observations, when ESK was roughly 5° southward and 5° eastward of the satellite footprint region; the white lines indicate the approximate temporal extent of the wave. (b-d) Change in the phase of Very-Low-Frequency (VLF) signals transmitted from the transmitters at Anthorn, UK (GQD) and Skelton, UK (GBZ), at the receivers at Ny-Ålesund, Norway (NYA) and Reykjavik, Iceland (REY), respectively, relative to the quiet-time curve, indicative of energetic particle precipitation occurring along each of the VLF ray paths: (b) from GQD to NYA; (c) from GBZ to NYA; (d) from GQD to REY. Credit: Hendry et al. [2020], Figure 2
Source: Geophysical Research Letters

A long-standing question about electromagnetic ion cyclotron waves (EMIC) in the Earth’s magnetosphere is the energies and rates at which they interact with the energetic electrons. A related question is how this interaction drives the precipitation of the energetic electrons into the upper atmosphere. Both questions are due to our lack of precise knowledge on the spatial scale size of EMIC activity regions.

Hendry et al. [2020] effectively turn the combination of two orbiting satellites (the NASA Van Allen Probe B and the Japanese Arase) and a ground sub-ionospheric Very-Low-Frequency (VLF) network into a powerful “magnetosphere-ionosphere observatory”.

By combining the observations from the different space- and ground-based platforms, the authors successfully determine the longitudinal extent of the EMIC source region. In the process, the combination demonstrates the growing power of such “heliospheric observatories” for tackling long-standing questions of the Sun-Earth system.

Citation: Hendry, A. T., Santolik, O., Miyoshi, Y., Matsuoka, A., Rodger, C. J., Clilverd, M. A., et al. [2020]. A multi‐instrument approach to determining the source‐region extent of EEP‐driving EMIC waves. Geophysical Research Letters, 47, e2019GL086599.

—Andrew Yau, Editor, Geophysical Research Letters

Text © 2020. The authors. CC BY-NC-ND 3.0
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