Processes in the Magnetospheric Boundary Layer

Abstract

The earth's magnetopause is a boundary that separates two distinctly different plasma regions - the (shocked) solar wind and the hot magnetospheric plasma controlled by the terrestrial magnetic field. Through this boundary a small fraction of the solar wind energy and momentum is transferred. This energy powers all major plasma processes within the magnetosphere. Thus, a proper understanding of boundary layer phenomena is of vital importance for magnetospheric plasma physics.An overview of the two main theories put forward to explain the energy and momentum transfer processes near the earth's magnetospheric boundary - magnetic merging/reconnection and the boundary layer dynamo model - will be given. The theories are compared with recent in situ plasma observations in the vicinity of the magnetopause.It is suggested here that internal processes in the magnetospheric boundary layer are decisive for the transfer of energy and momentum into the inner magnetosphere, which is coupled to the high latitude ionosphere. On the other hand, external conditions at the magnetopause proper determine the coupling to the solar wind.Means of relating transient magnetic field signatures, such as flux transfer events, with plasma dynamo induced currents will also be discussed.