Analysis of the Alfven transition layer in the cusp region by the use of 3D global particle-in-cell simulations

Abstract:

Three-dimensional (3D) global full electromagnetic particle-in-cell (PIC) simulations are used in order to analyze the cusp region within the frame of the global solar wind- terrestrial magnetosphere interaction when the Interplanetary Magnetcic Field (IMF) is in a northward configuration. Recent results of PIC simulations (Cai et al., 2014) have recovered the general expected features of the cusp issued from both previous experimental and MHD simulation results. One new striking feature was the evidence of an Alfven transition layer (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 in a good agreement with experimental data statistics performed by Lavraud and al. (2005) but not mentionned in MHD results. In complement to these experimental results, present simulations displayed in the image show that (i) the ATL largely extends out of the upper cusp region until even reaching the subsolar region, (ii) the ATL presents some assymetry around the meridian plane ; (iii) it has a 3D structure which is analyzed in details (not performed before); (iv) the middle region of the ATL (3D) located above the upper cusp presents a depletion where its width is much thinner and corresponds to a privilegied region where large plasma flows are observed which suggests strong local plasma precipitation. We take advantage of the 3D PIC simulations in order to analyze carfefully this area and plasma précipitation, and to separate plasma flows passing through the nearby reconnection lobes located along the magnetopause (and above the ATL) from those which do not. The main goal is to establish a link between the 3D dynamic of the reconnection lobes and of the upper cusp region.