The dc electric field detector onboard the instrumented portion of the Trigger payload detected a large-amplitude (~200 mV/m) electric field pulse which was observed with a time delay consistent only with an electromagnetic wave. A model for this perturbation is constructed in this paper and the associated field-aligned current calculated as a function of altitude. Near the explosion point, downward currents of 2500 &mgr;A/m2 and upward currents of 90 &mgr;A/m2 are indicated by the model. The lower upward current has the same direction as the field-aligned current in discrete auroral arcs. Taking into account the attenuation of the wave and the changes in Alfven speed and plasma density, the associated differential drift velocity between electrons and ions is found to peak at 750-km altitude at a value one-third of the electron thermal speed. This is well above the threshold for ion cyclotron wave turbulence and approaches the value necessary for production of electrostatic shocks or double layers. The differential velocity associated with the downward current well exceeds the electron thermal speed. The time delay for observation of accelerated electrons is consistent with the Alfven propagation time to 750-km altitude. The initial explosion pulse had internal temporal variations just above the oxygen ion cyclotron frequency in agreement with other experiments of this type. The Poynting flux in the electromagnetic pulse was sufficiently intense to create the observed particle precipitation.