Magnetosheath cavities: case studies using Cluster observations

Abstract. This paper presents examples of magnetosheath cavities in Cluster spacecraft observations. The cavities are accompanied by high energy particles in the magnetosheath and characterized by depressed magnetic fields and densities. Flow speeds decrease and temperatures increase within the cavities. All magnetosheath parameters show increased variability within the cavities when the energetic particle flux is high. We predict outward motion of the magnetopause boundary in response to the decreases in the magnetosheath ram pressure caused by the high energy particles within the magnetosheath cavities. For our events, the magnetopause distance is predicted to be 30% larger during the times of high energy particle flux in the magnetosheath than that predicted using concurrent upstream solar wind pressure observations. Our events show no preference to occur for a particular IMF direction or solar wind plasma condition.