Comparative Study of Mirror Mode Storms Inside Sirs and in Icmes' Sheaths

This work focuses on comparing the characteristics of mirror mode storms observed in ICMEs with the storms observed inside SIRs. Mirror mode oscillations shaped as peaks and holes have been identified using STEREO high resolution magnetic field data. They appear as closely spaced structures with durations over minutes and hours and have been called "mirror mode storms". Such structures have been frequently found inside SIRs close to their leading edge. We have found that mirror mode storms can appear in both, SIRs with and without forward shocks. In this work we look for mirror mode storms observed inside the sheaths behind ICME shocks detected by STEREO. We make special emphasis in the sheaths associated to fast ICMEs. Since shocks ahead of fast ICMEs usually have high Mach numbers, their sheaths can be very perturbed and this can lead to plasma instabilities such as the mirror mode instability.