We simulate plasma transport from the plasma sheet to the ring current, for the first time including the feedback effect of the drifting particles on both the electric and magnetic fields. Results suggest that strong, steady adiabatic convection throughout the middle plasma sheet leads to a highly stretched inner plasma sheet, but no ring current particle flux increases. We subsequently impose a substantial reduction of the specific entropy PV5/3 near midnight outside 10 RE, where P is particle pressure and V = ∫ds/B is flux tube volume. This produces a strong enhancement of the asymmetric ring current, which becomes symmetric when the pressure depletion and strong convection are quelled. We suggest that a reduction of the specific entropy in a region of the inner plasma sheet, apparently by some process that violates the assumption of adiabatic drift, plays a major role in the injection of a storm-time ring current.