Global Asymmetry of Hot Flow Anomalies

We conduct a 3-D global hybrid simulation for the interaction of the Earth’s bow shock with a solar wind directional tangential discontinuity (TD) whose normal lies in the equatorial (z=0) plane. Although the convection electric field points into the TD from one side of the discontinuity on both sides of the equator, the interaction only generates an HFA in the southern hemisphere. HFA generation results from bow shock-reflected ions energized by the inward-pointing electric field on one side of the TD and inward ion gyration on the other side.  The latter phenomenon only occurs south of the equator due to the global bow shock geometry. The global HFA asymmetry is driven by a reversal in the north-south component of the ion velocities at the bow shock in the two hemispheres, such that the ions gyrate into (away from) the TD in the southern (northern) hemisphere.  Our results indicate that HFAs must generally exhibit north-south and dawn-dusk asymmetries.