Identification and Statistical Analysis of Hot Flow Anomalies Using Cluster Multi-Spacecraft Measurements

Discovered nearly 20 years ago near the Earth's bow shock, the identification and separation of Hot Flow Anomalies (HFAs) from other events is still under debate. We have used the observations of instruments FGM, CIS, and RAPID aboard the four Cluster spacecraft to detect and study these phenomena. The definition and basic features of HFAs (size, direction of tangential discontinuity, electric field, speed of propagation) have been refined, several series of events identified, and a preliminary statistical analysis carried out. After combining data from RAPID and FGM the pitch angle distributions of protons have been calculated. The measured and calculated features of HFA events are confronted with the results of hybrid simulations.