Observations of magnetospheric high-m poloidal waves by ST-5 satellites in low Earth orbit during geomagnetically quiet times

TitleObservations of magnetospheric high-m poloidal waves by ST-5 satellites in low Earth orbit during geomagnetically quiet times
Publication TypeJournal Article
Year of Publication2015
AuthorsChi, PJ, Le, G
JournalJournal of Geophysical Research: Space Physics
Date Published05/2015
Keywordsdrift Alfven ballooning mode; high-m waves; poloidal mode
AbstractThe poloidal waves with large azimuthal wavenumbers (m~100) in the magnetosphere are known to be generated by drift or drift bounce resonance with energetic ring current particles, and these waves may play a role in modulating the energetic particles in the inner magnetosphere. When examining the magnetic field data collected by the NASA ST-5 satellites in the low Earth orbit, Le et al. [2011] discovered many wave events with frequencies of 30–200 mHz (in the Pc 2–3 band), and they proposed that these waves should in fact be Doppler-shifted high-m poloidal waves in the magnetosphere with frequencies at only a few mHz (in the Pc 5 band). Using a new method that examines the differences in wave phase detected by the three ST-5 satellites, we confirm that the frequencies in the Earth frame for the poloidal waves observed are mainly between 3 and 5 mHz. Not only were poloidal waves observed frequently by ST-5 in the dayside magnetosphere, but they were also occasionally seen in the nightside when the satellites passed through the same L shells. In each wave event, the azimuthal wavenumber may change with L, but the wave frequency in the Earth frame remains the same. We also find that poloidal waves can last more than 9 hours during geomagnetically quiet conditions, suggesting that even a very weak ring current can supply enough energetic particles to excite poloidal waves.
URLhttp://doi.wiley.com/10.1002/2015JA021145
DOI10.1002/2015JA021145
Short TitleJ. Geophys. Res. Space Physics


Page Last Modified: June 4, 2015