Detection of Hertz Frequency Multiharmonic Field Line Resonances at Low-L (L = 1.1–1.5) During Van Allen Probe Perigee Passes

F. R. Lena, L. G. Ozeke, J. R. Wygant, S. Tian, A. W. Breneman, I. R. Mann

Research output: Contribution to journalLetterpeer-review

Abstract

We present new and previously unreported in situ observations of Hertz frequency multiharmonic mode field line resonances detected by the Electric Field and Waves instrument on-board the NASA Van Allen probes during low-L perigee passes. Spectral analysis of the spin-plane electric field data reveals the waves in numerous perigee passes, in sequential passes of probes A and B, and with harmonic frequency structures from ∼0.5 to 3.5 Hz which vary with L-shell, altitude, and from day-to-day. Comparing the observations to wave models using plasma mass density values along the field line given by empirical power laws and from the International Reference Ionosphere model, we conclude that the waves are standing Alfvén field line resonances and that only odd-mode harmonics are excited. The model eigenfrequencies are strongly controlled by the density close to the apex of the field line, suggesting a new diagnostic for equatorial ionospheric density dynamics.

Original languageEnglish (US)
Article number2020GL090632
JournalGeophysical Research Letters
Volume48
Issue number1
DOIs
StatePublished - Jan 16 2021

Bibliographical note

Funding Information:
I. R. Mann is supported by a Discovery grant from Canadian NSERC. This research was supported by funding from the Canadian Space Agency through a Geospace Observatory (GO) Canada Science and Applications grant. The authors acknowledge the WDC for Geomagnetism, Kyoto University, Japan, for the geomagnetic indices (http://wdc.kugi.kyoto-u.ac.jp/). The authors also acknowledge use of NASA/GSFC's Space Physics Data Facility's OMNIWeb service and OMNI data.

Funding Information:
I. R. Mann is supported by a Discovery grant from Canadian NSERC. This research was supported by funding from the Canadian Space Agency through a Geospace Observatory (GO) Canada Science and Applications grant. The authors acknowledge the WDC for Geomagnetism, Kyoto University, Japan, for the geomagnetic indices ( http://wdc.kugi.kyoto-u.ac.jp/ ). The authors also acknowledge use of NASA/GSFC's Space Physics Data Facility's OMNIWeb service and OMNI data.

Publisher Copyright:
© 2020. American Geophysical Union. All Rights Reserved.

Keywords

  • field line resonance
  • ionosphere
  • magneto-seismology
  • magnetosphere
  • plasmasphere
  • standing Alfvén waves

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