Observations of the LLBL spatial profile and mechanisms of its formation

The low-latitude boundary layer (LLBL) serves as an interface between the Earth's magnetosheath and plasma sheet. A study of the spatial profile of the LLBL is important for understanding processes involving formation of this layer as well as plasma transfer processes across the magnetopause. We use the THEMIS as well as Interball-1 projects because they are a unique tool for the LLBL investigation due to their highly elliptical orbit and frequent magnetopause crossings. The different types of the LLBL spatial profiles were reported depending on upstream solar wind (magnetosheath) conditions. The direction of the interplanetary magnetic field (IMF) Bz component seems to play a crucial role for the LLBL morphology. We present the detailed analysis of the LLBL profile under different IMF orientations. We demonstrate monotonous changes of the ion density and temperature over a distance of about 1 RE under the northward pointing IMF and a strongly different LLBL profile during long-lasting southward IMF with no presence of the outer part of the LLBL. Moreover, the evolution of the LLBL profile is demonstrated using abrupt changes of the IMF orientation.