We present preliminary results from time dependent 2-dimensional numerical modelling of the magnetohydrodynamic interaction of the solar wind with the magnetosphere. A southward solar wind field produces a magnetospheric topology consistent with Dungey's model. The interaction appears to be fundamentally unsteady; the shock, magnetosheath, and magnetopause are highly turbulent. We model a ''substorm'' as the passage of a rotational discontinuity over the magnetosphere; we observe the the onset of enhanced reconnection in the magnetospheric tail produces a closed magnetic island which convects downstream.