Statistical Characterization of the Dynamic Near-Earth Plasma Sheet Relative to Ultra-Low Frequency (ULF) Wave Growth at Substorm Onset

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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Magnetospheric substorms are a complex phenomenon. During the initial stages of a substorm a variety of important processes occur in near-Earth space within a span of several minutes. The relative timing and links between these processes are critical to understanding how, where and when substorms may occur. One of the first observed signatures at substorm onset is the exponential increase in ULF (Ultra-Low Frequency) wave power in the near-Earth magnetotail (e.g., −7.5 ≤ XGSM ≤ −12.5 RE). We use the Time History of Events and Macroscale Interactions during Substorms spacecraft to examine the conditions in the magnetotail plasma sheet before, during and after local ULF wave growth. Prior to the ULF wave growth, the magnetotail stretches with convectional flows dominating. We then find strong earthward and azimuthal flows that peak at a similar time to the peak ULF wave power. These flows are found to be faster in the mid-tail (−10 ≤ XGSM ≤ −12.5 RE) than the near-tail (−7.5 ≤ XGSM ≤ −10 RE). Examining the local plasma energy density (magnetic, thermal and kinetic), we find no statistical decrease that could explain the exponentially growing ULF waves, in fact the local energy density is found to increase. This suggests that there may be an injection of energy from elsewhere in the magnetotail. Following the peak ULF wave power the tail is seen to dipolarize, and the local energy density is enhanced.
Original languageEnglish
Article numbere2022JA030491
Number of pages16
JournalJournal of Geophysical Research: Space Physics
Volume128
Issue number1
Early online date19 Jan 2023
DOIs
Publication statusPublished - Jan 2023

Fingerprint

Dive into the research topics of 'Statistical Characterization of the Dynamic Near-Earth Plasma Sheet Relative to Ultra-Low Frequency (ULF) Wave Growth at Substorm Onset'. Together they form a unique fingerprint.

Cite this