It is shown that the flux increases of trapped ions and electrons observed by Explorer 45 at L?4 during two large geomagnetic stroms can be quantitatively explained by a 1--3 RE inward radial displacement of the preexisting trapped particle distribution. This proposed source for the storm time ring current at L?4 requires only the acceleration of the previously existing trapped particle population via inward displacement under conservation of the first two adiabatic invariants. No source of new trapped particles at L?4 is required. Is was not possible to test whether such an inward radial displacement can account for storm time flux increases at any radial distances beyond L=4; however, the existence of particle losses implies that new particles are injected into the trapping region beyond L=4. The required inward radial displacement of the trapped particles can be explained by an equatorial electric field with an average azimuthal component of ~0.3--1.0 mV/m, which is a factor of 2 or 3 greater than electric fields observed within the plasmasphere in association with typical, nonstorm time, substorm activity. It is suggested that a significant difference between large geomagnetic storms and typical substorm activity may be inward convection occurring over a large (>270 ¿) longitude range during storms but only over a small (≲90 ¿) longitude range during typical substorms.