Structure and thickness of plasma depletion layer in MHD models and comparisons with themis observations

Abstract

When the magnetic field piles up against the dayside magnetopause, plasma depletion layer (PDL) is formed with decreasing plasma density and increasing magnetic field in front of the magnetopause boundary layer. Most of the PDL events were observed when the Interplanetary Magnetic Field (IMF) direction is northward. In this study, we examined a magnetosheath passage, including two clear PDL intervals, observed by THEMIS spacecrafts (B and D) in June 2, 2007. In order to understand the relationship between the PDL and upstream solar wind conditions, ACE spacecraft is used as Interplanetary Magnetic Field (IMF) and solar wind plasma monitor. Our observational findings verify those of previous studies that these two observed plasma depletion layers occurred during the northward IMF condition as well. We did not see any specific dependence on the solar wind plasma conditions in these plasma depletion layers. In addition to all these, the PDL observations and the results from the MHD models (OpenGGCM and BATSRUS) are compared for studying the characteristics of PDL. The OpenGGCM are seen to depict the variations observed in the THEMIS data better while these are seen to be smoothed out in BATSRUS results. By examining visually the magnetic field and density contours of simulations in XZ and XY planes, we determined the change in thickness of PDL. It is seen that the thickness increases both in magnetic local time and latitude. Plasma depletion layer was found to be thinnest at the subsolar point and increases with latitude. In addition, we see that PDL becomes thicker and weaker towards the flanks. Density contours give better signatures to illustrate the thickness of plasma depletion layer.