THE AIM OF THE PROPOSED INVESTIGATION IS TO CHARACTERIZE THE TIME-VARYING EARTH S RADIATION ENVIRONMENT DUE TO SEP AND CGRS AND RESPONSE OF THIS ENVIRONMENT TO THEIR TEMPORAL VARIABILITY AFFECTED BY THE SUN. IN ORDER TO ACHIEVE THESE GOALS WE WILL DETERMINE FLUXES AND ENERGY SPECTRA OF SEP AND GCRS IN THE REGION STARTING FROM THE MAGNETOPAUSE TO THE LEO S ALTITUDES. IN THIS INVESTIGATION WE WILL ANALYZE ENERGETIC PROTON SPACECRAFT OBSERVATIONS AND USE THEM FOR THE MODEL VALIDATION. THE NECESSARY MODELING THAT WILL BE PERFORMED AS A PART OF THE PROPOSED STUDY INCLUDES TWO MAJOR COMPONENTS: 1) KINETIC SIMULATION OF SEP AND GCRS BY TRACING THEM IN THE MAGNETOSPHERE STARTING FROM THE MAGNETOPAUSE TO THE LEO S ALTITUDES AND 2) MHD MODELING OF THE MAGNETOSPHERE TO OBTAIN THE GLOBAL VARIATIONS OF MAGNETIC AND ELECTRIC FIELDS. THE NOVEL FEATURE OF OUR APPROACH IS THAT THE NECESSARY MODELING OF THE MAGNETOSPHERE SEP AND GCRS WILL BE PERFORMED SIMULTANEOUSLY AS TWO PART OF THE SAME MODEL RUN WHERE A MAGNETIC FIELD ACTING UPON ENERGETIC PARTICLES WILL BE TIME-DEPENDENT AND UPDATED AS MODELING OF THE MAGNETOSPHERIC PLASMA PROGRESSES. DISTRIBUTION AND ENERGY SPECTRA OF SEP AND GCRS IN THE MAGNETOSPHERE WILL BE DETERMINED BY TRACKING THEIR TRAJECTORIES STARTING FROM THE MAGNETOPAUSE WHERE THEY ARE INJECTED INTO THE MAGNETOSPHERE. FLUX AND ENERGY SPECTRUM OF SEP AT THE MAGNETOPAUSE WILL BE DERIVED FROM MODELING OF THE SEP PROPAGATION FROM THE SUN TO THE EARTH PERFORMED WITH THE FIELD-LINE-ADVECTION MODEL FOR SOLAR PARTICLE ACCELERATION (FLAMPA) MODEL. PARAMETERS OF GCRS AT THE MAGNETOPAUSE WILL BE SPECIFIED WITH THE ISO-15390 MODEL.