A GLOBALLY INTEGRATED SUBSTORM MODEL - TAIL RECONNECTION AND MAGNETOSPHERE-IONOSPHERE COUPLING

We present a globally integrated substorm (GIS) model in which the pat chy-bursty tail reconnection process at similar to 20-35 R-E and the m agnetosphere-ionosphere (M-I) coupling process form a global feedback system to cause substorms. We identify the necessary and sufficient co nditions for the expansion onset in the near-Earth plasma sheet. The n ecessary condition for substorm onset is an abrupt convection braking in the near-Earth plasma sheet at a rate greater than or equal to simi lar 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 suff icient condition requires the disrupted tail current to be carried awa y by the Alfven wave to form the substorm current wedge. These conditi ons must be satisfied by any onset mechanism. The Alfven wave launched by the dipolarization-induced electric field must carry away the disr upted tail current from the dipolarization region. As an example, we s how 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-induc ed electric field of similar to 14 mV/m. Substorm expansion onset in t he ionosphere occurs similar to 1 min later when the Alfven wave is re flected at the ionosphere. The dipolarization-induced tail reconnectio n and the M-I coupling form a feedback system to power the ongoing exp ansion phase which typically lasts similar to 30 min. As the dipolariz ing region expands tailward, the expansion phase turns into recovery p hase when the local tail current becomes too weak to sustain the expan sion phase and the aurora activities start to retreat equatorward.