Geomagnetotail dynamics: Different types of equilibriums and transitions between them

Abstract

Two time scales are distinguished in the geomagnetotail dynamics. The small scale (T1) corre� sponds to disturbances propagating in the tail lobes, which have a relatively strong magnetic field and low plasma density. The larger scale (T 2 ) corresponds to plasma motions in the plasma sheet and has a relatively weak magnetic field and a relatively higher density. A disturbance, which is initiated by a localized burst of magnetic reconnection and appears in the geomagnetotail on the time scale T1, generates the upset of equi� librium in the plasma sheet zones with intermediate spatial dimensions (about RE). The theoretical consid� erations and numerical simulation indicate that the relaxation process, which subsequently proceeds on the larger time scale (T 2 ), results in the appearance of extremely thin embedded current sheets and in the gener� ation of fast plasma flows. This process gives an effective mechanism by which the magnetic energy stored in the geomagnetotail is transformed into the plasma flow kinetic energy. Such fast flows can also generate eddy plasma motions on smaller spatial scales. On the one hand, fast MHD components of this process carry a dis� turbance in other plasma sheet zones, where new magnetic reconnection bursts can originate at a large dis� tance from the zone of an initial nonlinear disturbance. As a result, new recurrent processes of relaxation orig� inate on the T2 time scale. Alternation originating in such a way is apparently the characteristic feature of eddy disturbances actually observed in the plasma sheet.