The response of the Earth's magnetosphere to the passage of interplanetary magnetic clouds is simulated using a three-dimensional magnetohydrodynamic (MHD) model. The input solar wind condition is given by the magnetic field, particle density, and plasma flow calculated from a model magnetic cloud. The cross-polar potential (&PHgr;p), Joule heating and electron energy precipitation into the polar cap are calculated. Synthetic magnetic indices Dst* and AE* are defined to serve as surrogates for the usual Dst and AE indices, respectively. We demonstrate that &PHgr;2p provides a good predictor of the energy deposition into the ionosphere during storm conditions and that Dst* and AE* behave qualitatively similarly to Dst and AE. ¿ American Geophysical Union 1995