This project aims to address the electromagnetic waves in Earth's magnetic field (magnetosphere) on charged particles, electrons specifically. This work is timely and highly relevant for improving the modeling and prediction of radiation belt electrons, which are of considerable practical importance due to their potential hazards to space systems. Specifically, radiation hazards have damaging effects on spacecraft through surface and internal charging. The research is directed towards advancing our understanding of the fundamental physical processes in the inner magnetosphere and dynamics of the radiation belt. The results will be utilized to improve current radiation belt modeling capabilities. This project also supports two early career scientists and a doctoral student. The findings of this project will be incorporated into a new introductory course in magnetospheric physics that the lead Principal Investigator is developing at University of Texas-Dallas .This project is a unified investigation, taking advantage of both observations and modeling, to quantify the effect of equatorial magnetosonic (MS) waves on energetic electron dynamics in the inner magnetosphere. MS waves have gained an increasing amount of attention in the research community, due to their potential mechanism for electron acceleration via Landau resonance, and their scattering of equatorially mirroring electron via bounce resonance. Recent Van Allen Probes observations have revealed the formation of electron butterfly distributions associated with MS waves, and in-situ modulation of the electron pitch angle distribution by the MS waves. The dynamics of equatorially mirroring electrons is important scientific question, which currently is not implemented in radiation belt models. This project will address the three fundamental scientific questions: What is the relation between MS waves and the electron butterfly pitch angle distribution in the inner magnetosphere? How do electron transport coefficients depend on magnetosonic wave normal and wave spectra and background plasma parameters? And how can bounce resonance effects be incorporated into models? To address these questions,  high-resolution wave and particle measurements from the twin Van Allen Probes will be analyzed. Test particle simulations will be carried out to calculate the electron transport coefficients as a function of pitch angle and energy, and then perform a parametric study of those transport coefficients. Phase space density evolution due to MS waves will be modelled and compared with high-resolution electron pitch angle distributions from Van Allen Probes.