Cold Dense Magnetopause Boundary Layer Under Northward IMF: Results From THEMIS and MHD Simulations

A layer of nearly stagnant cold dense plasma is observed by THEMIS spacecraft on a closed field region immediately inside the dayside magnetopause near the low latitude boundary layer on 3 June 2007. Using the OpenGGCM global MHD magnetosphere numerical model, we successfully reproduce this observed cold dense plasma layer in the simulation. The simulation results show that reconnection first occurs poleward of the cusp in the northern hemisphere, creating new open field lines extending southward and forming an open field layer; then subsequently occurs in the other hemisphere, creating new closed field lines that capture the magnetosheath plasma and form the dayside cold dense plasma layer. In this event, the open layer and the skin of the cold dense plasma layer have a southward tangential flow while the inner part of the cold dense plasma layer has a more stagnant and more turbulent flow.