Sub-storms-model predictions and observations

Summary form only given, as follows. A model for substorm breakup based on the formation of a coupled current wedge structure within an enhanced conductivity channel has been developed. Self-consistent prebreakup solutions have been obtained for dipolar collapse on closed field lines. The results suggest that substorm onsets occur on closed field lines with moderate L-values. Perturbation of these theoretical solutions leads to an instability which may be related to the onset of the expansion phase of the substorm. The instability criterion is satisfied where the magnetospheric westward convective flow is decelerated due to the presence of a local substorm wedge current system. Westward convective flows are expected to be more intense west of the Harang discontinuity (HD) as mapped, to the equatorial plane. This leads to a predominance of substorm onsets west of the HD. The model predictions were compared with experimentally observed prebreakup and expansive auroral arc structures