Convection in the distant magnetotail under extremely quiet and weakly disturbed conditions

Abstract

Measurements of the magnetic field and low-energy plasma by the Geotail spacecraft have been used to study magnetospheric convection in the distant tail at X = -(79 - 200) RE under extremely quiet and weakly disturbed conditions. The analysis was carried out separately for the tail lobes and the plasma sheet; these regions were identified by plasma and magnetic field parameters. It is shown that plasmas in the northern and southern tail lobes move tailward along magnetic field lines at the same time as magnetic field lines converge towards the plasma sheet. The main processes occurring in the distant tail under extremely quiet conditions (northward interplanetary magnetic field) and weakly disturbed conditions (southward IMF) are very similar, excluding the passage of high-speed tailward plasmoids, which are obviously generated in the near-Earth plasma sheet. Magnetic turbulence, that is, fluctuations of the magnetic field occurring against the background of a totally northward field (BZ>0), consistent with intense oscillations in the plasma flow VX component, is typical of all conditions. It is concluded that the stretched and antiparallel field lines of the northern and southern tail lobes are reconnected in the plasma sheet. Tail lobe plasma constantly enters the plasma sheet, where the lobe magnetic field energy converts into the kinetic energy of the plasma producing the magnetic turbulence. It seems likely that the direction (northward or southward) of the IMF is not necessary for tail formation, and processes in the near tail (substorm activity) does not strongly influence reconnection in the distant tail. Copyright 1999 by the American Geophysical Union.