Speaker
Description
The bulk of information on polarisation and propagation of ultra-low frequency (ULF, 1-1000 mHz) waves is normally obtained using ground-based magnetometer arrays. However, the ground ULF field observations may be significantly distorted by the transition of the magnetohydrodynamic wave into an electromagnetic wave at the boundary between the ionised and neutral parts of the atmosphere. These effects include polarisation rotation and spatial integration altering the spatial patterns of wave’s amplitude and phase. In this respect, high-frequency (HF, 3-30~MHz) radars comprising the Super Dual Auroral Radar Network (SuperDARN) enable in situ observations of the ULF wave parameters at ionospheric altitudes by measuring plasma drift variations caused by the wave’s electric field. This study utlises data from several SuperDARN radars covering mid-latitude and sub-auroral regions to identify the predominant polarisation modes and azimuthal wave numbers of evening-to-morning ULF events in the Pc5 frequency band (1.67-6.67 mHz). The observed statistics of these waves single out the solar wind dynamic pressure variations and Kelvin-Helmholtz instability at the magnetopause as their potential generation mechanisms, although the drift-bounce resonance with trapped energetic ions might be responsible for the small-scale eng of the observed Pc5 waves.
| Keyword-1 | ULF waves |
|---|---|
| Keyword-2 | SuperDARN |
