Effects of Bursty Bulk Flows on the Turbulence in the Plasma Sheet.

Abstract:

Recent studies have shown the importance of turbulent processes in the dynamics of the magnetosphere of the Earth, including plasma and energy transport and the plasma sheet stability. We studied the properties of the turbulent plasma sheet in the presence and in the absence of the bursty bulk flow events for different phases of geomagnetic substorms and for quiet geomagnetic conditions. The criteria used for the selection of BBFs are similar to ones established by Angelopoulos et al., (JGR, 1994). The classification of time intervals as quiet, expansion phase, and recovery phase was based on the variation of the AL-index (Stepanova et al., 2011). Statistical analysis was performed using the data of THEMIS probes during tail-science seasons. It was found that the plasma pressure is the parameter which experienced major variation if we compare the data for different substrom phases, and also in the presence and absence of BBFs: The radial plasma pressure profiles are steaper during the substorm expansion phase, the presence of BBFs smoothes this effect, especially during the recovery phase and the quiet time. Study of eddy diffusion showed that even in the absence of BBFs the plasma sheet is strongly turbulent. Analysis of bulk velocity data 20 minutes before and after a BBF showed that the BBFs could generate additional vorticity at the leading and trailing edges, but their contribution is not decisive.