Ballooning instability in the presence of a plasma flow: A synthesis of tail reconnection and current disruption models for the initiation of substorms

The drift ballooning mode (DBM) instability near the inner edge of the plas ma sheet (IEPS) is studied further by including a nonstationary earthward f low and flow shear in the analysis. Both equatorial and off-equatorial regi ons are considered. It is found that the presence of a decelerated earthwar d flow destabilizes both the M- and M+ branches of the DBM in a large porti on of the current sheet near the IEPS and substantially increases the growt h rate of the instability. The flow shear in the premidnight sector causes the conventional ballooning mode to weakly subside, while it slightly enhan ces the growth rate for the Alfvenic ballooning mode. The combination of th e earthward flow and flow shear makes both the Alfvenic ballooning mode and conventional ballooning mode grow much faster than they would without the flow, giving rise to coupled alfvenic slow magnetosonic waves, field-aligne d currents and the formation of a current wedge, a synthesis of tail reconn ection and cross-tail current disruption scenarios is proposed for the subs torm global initiation process: When the fast flow produced by magnetic rec onnection in the midtail abruptly decelerates at the IEPS, it compresses th e plasma populations earthward of the front, transports momentum to them, a nd pushes them farther earthward, This creates the configuration instabilit y in a large portion of the inner tail magnetic field lines on both the tai lward side and earthward side of the braking point.. As soon as the ionosph eric conductance increases over a threshold level, the auroral electrojet i s greatly intensified, which leads to the formation of the substorm current wedge and dipolarization of the magnetic field. This substorm paradigm com bines the near-Earth neutral line and near-Earth current disruption scenari os for the initiation of substorms and may also synthesize dynamical proces ses in the magnetosphere-ionosphere coupling and field line resonance durin g the substorm onset. We intend to use this global model to explain substor m expansion onsets occurring: under the southward interplanetary magnetic f ield condition.