THEMIS -
Scientific Aims

DEVELOPMENT OF SUBSTORMS

Currently there are two competing models to explain the substorm process: the Current-Disruption Model (CDM) und das Near Earth Neutral Line Model (NENL).

The CDM requires a local plasmainstability in the nightside magnetosphere at a distance of about 8-10 R_E, causing a disruption of the tail current in the magnetosphere and subsequent closure of this current in the ionosphere. As a result of this current disruption a rarefaction wave is generated, propagating tailward at large velocities and triggering magnetic reconnection at about a distance of 25 R_E.

In contrast to this the NENL requires magnetic reconnection at a distance of about 25 R_E as the trigger of the substorm process. So-called bursty bulk flows transport large amounts of energy into the inner magnetosphere where this energy is converted to thermal energy and flow diversion around the Earth at the inner edge of the plasma sheet occurs. The field-aligned currents of the substorm current wedge are generated by the process.