Parametric dependencies of spontaneous hot flow anomalies

摘要

Parametric dependencies of spontaneous hot flow anomalies at the quasi-parallel bow shock are investigated using global hybrid (kinetic ions and fluid electron) simulations with a variety of solar wind Mach numbers and directions of the interplanetary magnetic field (IMF). Simulations with solar wind Alfvénic Mach number of 3 and small IMF cone angles (with the flow velocity) show sporadic formation of spontaneous hot flow anomalies (SHFAs). Increasing the Mach number shows the formation of copious number of SHFAs whose properties are examined in this study. It is shown that the duration of SHFAs does not show much variation with Mach number indicating that their size generally increases with Mach number. Additionally, the level of solar wind deceleration associated with SHFAs increases with Mach number as does the core ion temperature. It is also found that the edges of SHFAs are associated with jumps in magnetic field that increase with shock Mach number. The results also show that the rate of SHFA formation increases with increasing Mach number. Simulations with IMF cone angle of 90° show that SHFAs form at the quasi-parallel bow shock provided the shock Alfvén Mach number is ~>3. This shows that SHFAs may form at all cone angles.