Statistical Study of Shock Non-Stationarity

Owing to the high temporal resolutions of FPI/DIS, MMS can resolve the fine structure of the shock ramp, which often shows presence of holes in reduced ion-phase space distributions (integrated along the tangential plane of the shock). Such holes have been associated with rippling propagating along the shock surface, but also have been observed in association with the shock reformation. In this study, we have focused on characterizing ion phase-space holes at the Earth’s bow shock using MMS observations. We use a machine learning approach to automatically identify shock crossings using the FPI/DIS data. We compile a database of those crossings including various spacecraft-related and shock-related parameters for each event. We select ~500 shock crossings with burst data and establish a systematic procedure to find the shocks exhibiting phase space holes. We characterize the occurrence of the holes as a function of shock parameters such as Mach number and geometry. These results are important to understanding the non-stationary behavior of collisionless shocks