A Multi-Instrument Study of a Dipolarization Event in the Inner Magnetosphere

H. Matsui, R. B. Torbert, H. E. Spence, M. R. Argall, I. J. Cohen, M. B. Cooper, R. E. Ergun, C. J. Farrugia, J. F. Fennell, S. A. Fuselier, M. Gkioulidou, Yu V. Khotyaintsev, P. A. Lindqvist, A. Matsuoka, C. T. Russell, M. Shoji, R. J. Strangeway, D. L. Turner, H. Vaith, J. R. Wygant

Research output: Contribution to journalArticlepeer-review

Abstract

A dipolarization of the background magnetic field was observed during a conjunction of the Magnetospheric Multiscale (MMS) spacecraft and Van Allen Probe B on September 22, 2018. The spacecraft were located in the inner magnetosphere at L ∼ 6–7 just before midnight magnetic local time (MLT). The radial separation between MMS and Probe B was ∼1RE. Gradual dipolarization or an increase of the northward component BZ of the background field occurred on a timescale of minutes. Exploration of energization and Radiation in Geospace located 0.5 MLT eastward at a similar L shell also measured a gradual increase. The spatial scale was of the order of 1 RE. On top of that, MMS and Probe B measured BZ increases, and a decrease in one case, on a timescale of seconds, accompanied by large electric fields with amplitudes > several tens of mV/m. Spatial scale lengths were of the order of the ion inertial length and the ion gyroradius. The inertial term in the momentum equation and the Hall term in the generalized Ohm's law were sometimes non-negligible. These small-scale variations are discussed in terms of the ballooning/interchange instability and kinetic Alfvén waves among others. It is inferred that physics of multiple scales was involved in the dynamics of this dipolarization event.

Original languageEnglish (US)
Article numbere2021JA029294
JournalJournal of Geophysical Research: Space Physics
Volume126
Issue number5
DOIs
StatePublished - May 1 2021

Bibliographical note

Funding Information:
This work was supported by NASA?s MMS contract NNG04EB99C and Van Allen Probes contract NAS5-01072.

Funding Information:
This work was supported by NASA’s MMS contract NNG04EB99C and Van Allen Probes contract NAS5‐01072.

Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.

Keywords

  • dipolarization
  • inner magnetosphere
  • multiple scale dynamics

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