Multiharmonic Toroidal Standing Alfvén Waves in the Midnight Sector Observed During a Geomagnetically Quiet Period

Kazue Takahashi, Massimo Vellante, Alfredo Del Corpo, Seth G. Claudepierre, Craig Kletzing, John Wygant, Kiyokazu Koga

Research output: Contribution to journalArticle


Excitation of toroidal mode standing Alfvén waves in the midnight sector of the inner magnetosphere in association with substorms is well documented, but studies are sparse on dayside sources for the waves. This paper reports observation of midnight toroidal waves by the Van Allen Probe B spacecraft during a geomagnetically quiet period on 12–13 May 2013. The spacecraft detected toroidal waves excited at odd harmonics below 30 mHz as it moved within the plasmasphere from (Formula presented.) 2100 magnetic local time to (Formula presented.) 0030 magnetic local time through midnight in the dipole (Formula presented.) range 4.2–6.1. The frequencies and the relationship between the electric and magnetic field components of the waves are consistent with theoretical toroidal waves for a reflecting ionosphere. At the time of the nightside toroidal waves, compressional waves were observed by geostationary satellites located on the dayside, and the amplitudes of both types of waves varied with the cone angle of the interplanetary magnetic field. The nightside toroidal waves were likely driven by fast mode waves that resulted from transmission of upstream ultralow frequency waves into the magnetosphere. Ground magnetometers located near the footprint of the spacecraft did not detect toroidal waves.

Original languageEnglish (US)
Article numbere2019JA027370
JournalJournal of Geophysical Research: Space Physics
Issue number3
StatePublished - Mar 1 2020


  • ion foreshock
  • nightside magnetosphere
  • toroidal Alfvén waves
  • Van Allen Probe

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