ELF/VLF waves related to magnetospheric compression: conjugated observations from satellite- and subauroral ground-based instruments.

Abstract:

Using a VLF loop antenna located at subauroral latitudes in Athabasca (ATH), Canada (54.7N, 246.7E, L=4.3), we have been able to monitor almost ELF/VLF emissions almost continuously since September 2012. This data has allowed us to find a unique conjugate event of ELF/VLF waves between ATH and the RBSP-B satellite, associated with intense magnetic compression.

This event took place on December 23, 2014 at 11:17 UT (03:17 MLT) and lasted for a couple of minutes. It was observed just after an intense sudden commencement caused by an enhancement of solar wind speed (~330 to ~420 km/h) during northward IMF. Data from both sources show see a clear chorus emission with discrete elements (rising tones at ATH) centered at ~2 kHz. RBSP-B also sees a hiss-like emission at ~0.8 kHz, starting a minute before the chorus. We suggest the increasing magnetic field on the dayside, caused by the compression of the magnetosphere due to increased solar wind speed, caused betatron acceleration of plasma-sheet electrons. This leads to enhancement of the temperature anisotropy that regulates electron cyclotron instability and thus induced whistler-mode wave generation.

We use wave and particle measurements from RBSP-B to discuss the origins and properties of these emissions using both electric and magnetic field data. As the hiss-like emission started one-minute earlier than the chorus, we investigate if they were generated independently or if they instead correspond to upper and lower-band of a single emission. In addition, using electron flux data we examine possible relativistic electron acceleration caused by these chorus waves.