Solar wind induced processes in the magnetotail

Solar wind/IMF parameters and their variations influence the state and dyna mics of the magnetosphere in several different ways, and the plasma sheet p lays its own active role to form the magnetotail's response to external dri ving. This field is still quite controversial; key unsolved issues are thos e which probably involve the nonsteady, nonequilibrium and nonlinear charac ter of the system. This paper discusses an interesting development of conce pts concerning (1) plasma sheet convection, (2) mechanisms which initiate t he substorm onset, and (3) variability of tail dynamics. A remarkable examp le is a recognition of Bursty Bulk Flows as a basic way for the plasma shee t to sustain the convective transport of plasma, energy and magnetic flux v ia transient mesoscale dynamic structures. As concerns the substorm onset, the sharp change from the magnetic reconnection (NENL) model to processes i n the dipolar-like near tail is now moving into a synthetic stage. Here non -linear models of different coupled instabilities are actively explored to find a way to excite the tearing mode starting from a singular thin current sheet configuration which seems to form in the near tail prior to the brea kup. Variable responses to external drivers and the variability of substorm s compel a recognition of the magnetotail as a very complicated nonlinear o pen system which includes a hierarchy of coupled processes of different sca les. A unique fleet of magnetospheric spacecraft, simultaneously probing di fferent domains and supported by extensive ground observations, global imag ing and solar wind monitoring, now provides a real chance to understand the magnetotail as a global dynamic system. (C) 1999 Elsevier Science Ltd. All rights reserved.