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

摘要

High-time resolution CUTLASS observations andground-based magnetometers have been employed to study the occurrence ofvortical flow structures propagating through the high-latitude ionosphere duringmagnetospheric substorms. Fast-moving flow vortices (~800 m s-1)associated with Hall currents flowing around upward directed field-alignedcurrents are frequently observed propagating at high speed (~1 km s-1)azimuthally away from the region of the ionosphere associated with the locationof the substorm expansion phase onset. Furthermore, a statistical analysis drawnfrom over 1000 h of high-time resolution, nightside radar data has enabled thecharacterisation of the bulk properties of these vortical flow systems. Theiroccurrence with respect to substorm phase has been investigated and a possiblegeneration mechanism has been suggested.Key words: Ionosphere (auroral ionosphere; electricfields and currents) · Magnetospheric physics (storms and substorms)