Statistical study of foreshock bubbles, hot flow anomalies, and spontaneous hot flow anomalies and their substructures observed by MMS

THEMIS and Cluster observations show that some cores contain local density enhancements which can be studied to better understand the evolution processes of foreshock transients. However, closer examinations of these substructures were not feasible until the availability of the higher resolution data from the Magnetospheric Multiscale mission (MMS).

We identify 164 FB-like, HFA-like, and SHFA events from two MMS dayside phases for a statistical study to investigate their solar wind conditions, properties, and substructure properties. Occurrence rates of the three event types are higher for lower magnetic field strengths, higher solar wind speeds and Mach numbers, and quasi-parallel bow shocks. Events usually span up to 3 R-E along the bow shock surface and extend up to 6 R-E upstream from the bow shock.