IMF Control of the LLBL Structure and Thickness

Abstract:

A list of processes that can lead to the plasma transfer across the low-latitude boundary layer (LLBL) is long, and it has been broadly discussed in many papers but reconnection of magnetospheric and magnetosheath magnetic fields is believed to be a main contributor to this transfer. The paper presents a basic structure of two sublayers of the low-latitude boundary layer (LLBL) for northward and southward interplanetary magnetic field (IMF) orientations and shows that, regardless of different processes responsible for a formation and evolution of the entire LLBL, the outer part of the LLBL is significantly influenced by the sign of the IMF B_Z component. Under northward IMF conditions, this layer is present, whereas it is missing during a southward pointing IMF. This behavior can be understood in terms of a motion of reconnection spots due to changes of the orientation of the magnetosheath magnetic field in the vicinity of the magnetopause. Our case and statistical studies demonstrate that the changes of the LLBL structure can be observed in the subsolar region as well as on flanks near the dawn-dusk meridian. We briefly discuss effects of other magnetic field components and emphasize a role of magnetosheath magnetic field variations on the boundary layer formation.