MMS Observations 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. The dynamic pressure inside HFAs is lower than the ambient solar wind due to the density depletion and flow deflection. The passage of HFAs will therefore result in local negative pressure impulses, which lead to a local sunward expansion of the magnetopause. HFAs can also transmit compressional waves into the magnetosphere that can excite resonant ULF waves and cause particles to scatter into the loss cone and precipitate into the ionosphere, generate field-aligned currents in the magnetosphere that drive magnetic impulse events in the high-latitude ionosphere, and trigger transient auroral brightenings. NASA’s MMS mission produce unprecedented high resolution data, which enable the observations of HFA structures in great details.