In this report we use 0.1- to 32-keV H+ and O+ flux modulations observed during a large-scale dayside pulsation event at ~6RE near the equatorial plane on April 4, 1979, to estimate the azimuthal wave electric field and spatial radial gradient of the phase space densities for the two ion species as a function of energy. We first find that the average azimuthal electric field associated with the wave has an amplitude of approximately 10 mV/m; this electric field magnitude can cause field lines to be displaced ~1.5 RE during the course of an oscillation. Because of the large field displacement we can infer the ion distribution spatial radial gradients from a theoretical expression which describes the effects of a resonant hydromagnetic wave on a particle distribution. We find that for both H+ and O+, ∂f/∂R<0 for all energies. In addition, we find that the spatial scale length for changes in f for both O+ and H+ is generally of the order of several earth radii.