Solar wind energy transfer regions inside the dayside magnetopause—II. Evidence for an MHD generator process

Abstract

In this paper a quantitative analysis of magnetosheath injection regions observed by PROGNOZ-7 in the dayside high latitude boundary layer is performed. Particular emphasis is laid on describing the consequences of the observed excess transverse momentum of solar wind ions (H + and He 2+) as compared to the magnetospheric ions (e.g. He + and O +) in the magnetosheath injection regions, hereafter referred to as energy transfer regions. An important result of this study is that the observed excess drift velocity of the solar wind ions as compared to the magnetospheric ions can be interpreted as a negative inertia current being present in the boundary layer. This means that the inertia current goes against the local electric field and that particle kinetic energy is converted into electric energy there. The dayside high-latitude boundary layer therefore constitutes a voltage generator (at least with respect to the injected magnetosheath plasma). The MHD-theory predicts a strong coupling of the energy transfer process in the boundary layer and the ionosphere, both regions being connected by field aligned currents. The rate of decay of the inertia current in the injected plasma element is in the range of a few minutes, a value which is directly proportional to the ionospheric resistance. By taking into account both the Hall and the Pedersen conductivities in the ionosphere, the theory also predicts a strong coupling between ionospheric East/West and North/South currents. A considerable part of the inertia current may actually flow in the tangential (East/West) direction due to this coupling. Thus, a consequence of the boundary layer energy transfer process is that it may generate currents, powering other magnetospheric plasma processes, down to ionospheric heights.