Impact of the low/high Alfven Mach number regime of the solar wind on the Aflven transition Layer of the cusp for IMF North: 3D global PIC simulation.

 CLUSTER experimental observations of  Lavraud et al. (2005) have evidenced the presence of a particular layer (so –called herein Alfven Transition Layer or ATL) almost adjacent to the upper edge of the stagnant exterior cusp (SEC), through which the plasma flow transits from super-(from magnetosheath) to sub- (to SEC) Alfvenic regime as the interplanetary magnetic field (IMF) is northward. Three dimensional globa PIC simulations have been recently used  (Cai et al., 2015) to analyze the main features of the cusp for an IMF configuration similar that in the observations. These simulations have allowed us to complete the global view of the cusp region  (in particular the features not accessible by MHD approach).  A  detailed analysis has allowed to retrieve the features of the ATL which reveals to be associated to the complicated 3D particles entry into the cusp region and exhibit an internal conic depletion region (CDR) where the ion fluxes concentrate and are very strong (which suggests very local ion precipitation). Moreover, simulation results show that the ATL expands towards areas out and even far from the cusp region and outside the meridian plane.

                     In the present work, the study is extended for different Ma regimes of the solar wind, as the IMF stays in northward  configuration. Results show the impact of this Ma variation on the 3D features of the overall magnetosphere and in particular on the cusp region, i.e. (i) on the 3D ATL structures/spatial scales, (ii) on the extension of the region surrounded by the ATL, and (iii) on the structures, the spatial scales and the dynamics of the CDR itself.