CUTLASS HF radar observations of high-latitude azimuthally propagating vortical currents in the nightside ionosphere during magnetospheric substorms

Abstract. High-time resolution CUTLASS observations and ground-based magnetometers have been employed to study the occurrence of vortical flow structures propagating through the high-latitude ionosphere during magnetospheric substorms. Fast-moving flow vortices (~800 m s^-1) associated with Hall currents flowing around upward directed field-aligned currents are frequently observed propagating at high speed (~1 km s^-1) azimuthally away from the region of the ionosphere associated with the location of the substorm expansion phase onset. Furthermore, a statistical analysis drawn from over 1000 h of high-time resolution, nightside radar data has enabled the characterisation of the bulk properties of these vortical flow systems. Their occurrence with respect to substorm phase has been investigated and a possible generation mechanism has been suggested.

Key words: Ionosphere (auroral ionosphere; electric fields and currents) · Magnetospheric physics (storms and substorms)