A globally integrated substorm model: Tail reconnection and magnetosphere-ionosphere coupling

We present a globally integrated substorm (GIS) model in which the patchy-bursty tail reconnection process at similar to 20-35 R-E and the magnetosphere-ionosphere (M-I) coupling process form a global feedback system to cause substorms. We identify the necessary and sufficient conditions for the expansion onset in the near-Earth plasma sheet. The necessary condition for substorm onset is an abrupt convection braking in the near-Earth plasma sheet at a rate greater than or equal to similar to 3 (mV/m)/R-E, which is equivalent to dipolarizing the taillike field at a rate greater than or equal to similar to 0.5 nT/s. The sufficient condition requires the disrupted tail current to be carried away by the Alfven wave to form the substorm current wedge. These conditions must be satisfied by any onset mechanism. The Alfven wave launched by the dipolarization-induced electric field must carry away the disrupted tail current from the dipolarization region. As an example, we show that substorm expansion onset can be triggered by abruptly braking a bursty bulk flow of similar to 3 mV/m within similar to 1 R-E. The disrupted tail current at the expansion onset is similar to 10(5) A/R-E carried away by the Alfven wave launched by the dipolarization-induced electric field of similar to 14 mV/m. Substorm expansion onset in the ionosphere occurs similar to 1 min later when the Alfven wave is reflected at the ionosphere. The dipolarization-induced tail reconnection and the M-I coupling form a feedback system to power the ongoing expansion phase which typically lasts similar to 30 min. As the dipolarizing region expands tailward, the expansion phase turns into recovery phase when the local tail current becomes too weak to sustain the expansion phase and the aurora activities start to retreat equatorward.