Smith, AW;
Rae, IJ;
Forsyth, C;
Watt, CEJ;
Murphy, KR;
(2023)
Statistical Characterization of the Dynamic Near‐Earth Plasma Sheet Relative to Ultra‐Low Frequency (ULF) Wave Growth at Substorm Onset.
Journal of Geophysical Research: Space Physics
, 128
(1)
, Article e2022JA030491. 10.1029/2022ja030491.
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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.
| Type: | Article |
|---|---|
| Title: | Statistical Characterization of the Dynamic Near‐Earth Plasma Sheet Relative to Ultra‐Low Frequency (ULF) Wave Growth at Substorm Onset |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1029/2022ja030491 |
| Publisher version: | https://doi.org/10.1029/2022JA030491 |
| Language: | English |
| Additional information: | © 2023 The Authors. This is an open access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/). |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10163734 |
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