Recent Advances in the Physics of Hot Flow Anomalies

Abstract:

Hot flow anomalies (HFAs) are events observed near planetary bow shocks that are characterized by greatly heated solar wind plasmas and substantial flow deflection. HFAs are universal phenomena that have been observed near the bow shock of Earth, Venus, Mars, and Saturn. HFAs are not stable structures and they evolve with time. Statistical study shows that both ion and electron spectra can be used to classify young and mature HFAs. Classifications according to ion and electron spectra are not absolutely consistent, which might be due to different heating mechanisms and efficiency for ions and electrons. HFAs were also classified into four categories (“-+”, “+-”, “M”, and “W”) according their dynamic pressure profile. Most “W” type HFAs are mature HFAs (according to ion spectra) and most “-+” and “+-” type HFAs are young HFAs. Half of the “M” type HFAs are mature HFAs. Mature HFAs are pressure balanced while the pressure is higher inside young HFAs than that outside.