Diagnosing the Time‐Dependent Nature of Magnetosphere‐Ionosphere Coupling via ULF Waves at Substorm Onset

A. W. Smith*, I. J. Rae, C. Forsyth, C. E. J. Watt, K. R. Murphy, I. R. Mann

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Azimuthal structuring is usually observed within the brightening auroral substorm onset arc; such structure has been linked to the exponential growth of electromagnetic ultralow‐frequency (ULF) waves. We present a case study investigating the timing and frequency dependence of such ULF waves on the ground and in the near‐Earth magnetotail. In the magnetotail, we observe an increase in broadband wave power across the 10‐ to 100‐s period range. On the ground, the arrival times spread from an epicenter. The onset of longer period waves occurs first and propagates fastest in latitude and longitude, while shorter periods appear to be more confined to the onset arc. The travel time from the spacecraft to the ground is inferred to be approximately 1–2 min for ULF wave periods between 15 and 60 s, with transit times of 60 s or less for longer period waves. This difference might be attributed to preferential damping of the shorter period waves, as their amplitude would take longer to rise above background levels. These results have important consequences for constraining the physics of substorm onset processes in the near‐Earth magnetotail and their communication to the ground.
Original languageEnglish
Article numbere2020JA028573
Number of pages17
JournalJournal of Geophysical Research: Space Physics
Volume125
Issue number11
Early online date23 Nov 2020
DOIs
Publication statusPublished - Nov 2020

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