Evolution of the magnetic field configuration in the plasma sheet is modeled for an intense substorm event on March 19, 1978. The model is based on the idea that the substorm field-aligned currents are initiated in the ionosphere in response to an enhanced magnetospheric convection (Kan et al., 1988). The field-aligned currents in the model are determined from the ground-base magnetometer data with a time resolution of 5 min. The substorm field-aligned currents are assumed to close in the plasma sheet to complete the substorm current circuit. It is shown that the magnetic field produced by the substorm current system in the model can reproduce several important substorm signatures observed in the plasma sheet. These signatures include the taillike reconfiguration in the plasma sheet during the growth phase, the dipolarization of the plasma sheet associated with the substorm expansion onset, and the formation of a new X line. A shortcoming of the model is that the plasma dynamics in the plasma sheet have been ignored. In spite of this shortcoming, however, the model demonstrates that the ionosphere, in response to an enhanced magnetospheric convection, can cause the plasma sheet to change its magnetic configuration to result in the substorm signatures observed in the plasma sheet. The present study shows that it is possible for the ionosphere to play an active role in causing the observed reconfigurations of the plasma sheet during substorms. ¿American Geophysical Union 1991