Hot Flow Anomalies near the Bow Shock and Their Geoeffects

The Earth’s magnetic field carves out a cavity known as the magnetosphere in the solar wind ejected from the Sun’s upper atmosphere.  A bow shock standing upstream from the magnetosphere serves to decelerate and deflect the supersonic solar wind, enabling it to flow around the magnetosphere.  In gasdynamic and magnetohydrodynamic models, no information about the interaction reaches the region upstream from the bow shock.  However, when kinetic effects are considered, hot flow anomalies (HFAs) form upstream from the Earth’s bow shock. HFAs exhibit dramatic plasma heating (by a factor of 10) and enormous flow deflections (sometimes even backward toward the Sun). Because HFAs drive magnetopause boundary waves, 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, they are an essential aspect of the solar wind-magnetosphere-ionosphere interaction and deserve detailed study.  From a theoretical point of view, they provide a fascinating example of local (microscale) phenomena having global effects.  I will begin by providing a basic introduction to the Earth’s magnetospheric environment, introduce what are HFAs, why do we study them, and then describe evolutions of HFAs, I will then discuss particle heating inside HFAs, reconnection within an HFA, and the discovery of Spontaneous HFAs (SHFA). Finally, I will discuss an extreme HFA event greater than 10 Earth Radii and its geoeffects.