The roles of the magnetopause and plasmapause in storm-time ULF wave power enhancements

J. K. Sandhu*, I. J. Rae, F. A. Staples, D. P. Hartley, M.-T. Walach, Tom Elsden, K. R. Murphy

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


Ultra low frequency (ULF) waves play a crucial role in transporting and coupling energy within the magnetosphere. During geomagnetic storms, dayside magnetospheric ULF wave power is highly variable with strong enhancements that are dominated by elevated solar wind driving. However, the radial distribution of ULF wave power is complex - controlled interdependently by external solar wind driving and the internal magnetospheric structuring. We conducted a statistical analysis of observed storm-time ULF wave power from the Van Allen Probes spacecraft within 2012-2016. Focusing on the dayside (06 < magnetic local time ≤ 15), we observe large enhancements across 3 < L < 6 and a steep L dependence during the main phase. We consider how accounting for concurrent magnetopause and plasmapause locations may reduce statistical variability and improve parameterization of spatial trends over and above using the L value. Ordering storm time ULF wave power by L provides the weakest dependences from those considered, whereas ordering by distance from the magnetopause is more effective. We also explore dependences on local plasma density and find that spatially localized ULF wave power enhancements are confined within high density patches in the afternoon sector (likely plasmaspheric plumes). The results have critical implications for empirical models of ULF wave power and radial diffusion coefficients. We highlight the necessity of improved characterization of the highly distorted storm-time cold plasma density distribution, in order to more accurately predict ULF wave power.
Original languageEnglish
Article numbere2021JA029337
Number of pages14
JournalJournal of Geophysical Research: Space Physics
Issue number7
Early online date29 Jun 2021
Publication statusPublished - 12 Jul 2021


  • ULF waves
  • Geomagnetic storms
  • Van Allen Probes
  • Inner magnetosphere
  • Plasmasphere


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