THIS PROPOSAL ADDRESSES FST 3.1.3 STUDIES OF THE GLOBAL ELECTRODYNAMICS OF IONOSPHERIC DISTURBANCES. DERIVING STORM TIME IONO-SPHERIC ELECTRODYNAMICS IS OF PARTICULAR IMPORTANCE TO: LWS SSA-2 PHYSICS-BASED SATELLITE DRAG FORECASTING CAPABILITY; SSA-4 PHYSICS-BASED TEC FORECASTING CAPABILITY; AND SSA-5 PHYSICS-BASED SCINTILLATION FORECASTING CAPABILITY. WE PROPOSE TO DETERMINE STORM-TIME IONOSPHERIC ELECTRODYNAMICS FROM OBSERVATIONS AS FULLY AS POSSIBLE USING VARIOUS SATELLITE AND GROUND-BASED DATASETS AND QUANTITATIVELY TEST EXISTING EMPIRICAL AND PHYSICS-BASED MODELS THUS DERIVING ADVANCES IN MODELING CAPABILITIES TO IMPROVE QUANTITATIVE PREDICTIVE CAPABILITY OF STORM-TIME IONOSPHERIC ELECTRODYNAMICS. WE WILL (1) ASSESS STORM-TIME IONOSPHERIC ELECTRODYNAMICS FROM OBSERVATIONS INCLUDING THE IONOSPHERIC CONDUCTIVITY CURRENTS AND ELECTRIC FIELDS; (2) QUANTIFY THE VALIDITY OF EXISTING EMPIRICAL AND PHYSICS-BASED MODELS OF IONOSPHERIC ELECTRODYNAMICS; (3) IDENTIFY KEY AREAS OF DISCREPANCY AND ASSESS TECHNIQUES INCLUDING DATA-ASSIMILATION TO INCORPORATE AVAILABLE DATA INTO IONOSPHERE/THERMOSPHERE MODELS AND TO INFER EXTERNAL FORCING WHERE NOT WELL MEASURED; (4) TRANSLATE MODELED/ASSIMILATED GLOBAL ELECTRODYNAMICS TO BOTH MAGNETOMETER AND GIC MEASUREMENTS THAT CAN BE VALIDATED ON THE GROUND. THE STUDY WILL CONSIDER UNCERTAINTIES AND HOW THE SOURCES OF ERROR IMPACT THE RESULTS. NASA WILL FACILITATE INTERACTION WITH USER COMMUNITIES.