Wave activity inside hot flow anomaly cavities

Abstract

Low-frequency wave properties inside two hot flow anomalies (HFAs) at different stages of evolution are, for the first time, studied applying the k-filtering technique on multipoint measurements from the Cluster satellites. The observed wave activity in an HFA cavity in an early stage of its evolution was interpreted as the combination of inherent fluctuation in the solar wind and those of a plasma component specularly reflected at the Earth's bow shock, where the amplitude of the fluctuations had been enhanced by a plasma beam instability. The wave field of a more evolved HFA was found to be less complex but contained a periodicity in the wave number distribution with a period that is suggested to come from the geometry of the HFA cavity.