THE EARTH S MAGNETOSPHERE IS HIGHLY DYNAMIC. THROUGHOUT THE MAGNETOSPHERE THE PLASMA IS IN MOTION. ONE CONSEQUENCE OF THIS MOTION IS THE EARTHWARD TRANSPORT OF PLASMA ON CLOSED MAGNETIC FIELD LINES IN THE MAGNETOTAIL. AS THE PLASMA CONVECTS IT IS HEATED ADIABATICALLY AND THE PLASMA PRESSURE INCREASES. AS SUCH WHAT WAS PLASMA FLOW ENERGY IN THE OUTER MAGNETOSPHERE HAS BECOME THERMAL ENERGY IN THE INNER MAGNETOSPHERE. OR IN TERMS OF PRESSURE DYNAMIC PRESSURE FROM THE FLOW HAS BECOME THERMAL PRESSURE. THESE PRESSURES BOTH CONTRIBUTE TO THE FORCE BALANCE WITHIN THE PLASMA. THERE IS A THIRD CONTRIBUTOR TO THE FORCE BALANCE AND THAT IS THE FORCE ASSOCIATED WITH MAGNETIC FIELD PRESSURE AND CURVATURE THAT IS THE JXB FORCE. IN THE INNER MAGNETOSPHERE WHERE THE THERMAL PRESSURE FREQUENTLY DOMINATES THE DYNAMIC PRESSURE THE JXB FORCE MAINLY BALANCES THE THERMAL PRESSURE FORCE. BUT WHEN THE MAGNETOSPHERE IS DYNAMIC AS OCCURS DURING SUBSTORMS THE DYNAMIC PRESSURE BECOMES AN IMPORTANT CONTRIBUTOR. WHILE THE PLASMA MUST BE IN LOCAL FORCE BALANCE IN THE ABSENCE OF PARALLEL ELECTRIC FIELDS THE FIELD LINES ARE EQUIPOTENTIALS AND SINCE THE FIELD LINES THREAD THE IONOSPHERE ANY MAGNETOSPHERIC FLOW PATTERN MAPS TO THE IONOSPHERE. THE IONOSPHERE HOWEVER IS HIGHLY COLLISIONAL AND THE NEUTRAL ATMOSPHERE ACTS TO SLOW DOWN ANY IMPOSED FLOW. THERE MUST THEREFORE BE A JXB FORCE ACTING IN THE IONOSPHERE AS WELL TO OVERCOME THE FRICTIONAL DRAG FROM THE NEUTRALS. BECAUSE OF THE COLLISIONS THE IONOSPHERE IS GENERALLY DISSIPATIVE (J.E>0) AND THE MAGNETIC FIELD DOES WORK ON THE PLASMA. THE PERPENDICULAR CURRENTS THAT OVERCOME THE FRICTION MUST CLOSE VIA FIELD-ALIGNED CURRENTS TO REGIONS WERE THE CURRENTS ARE GENERATED I.E. J.E<0. THIS COUPLING IS INHERENTLY COMPLEX SINCE WITHIN THE MAGNETOSPHERE THERE ARE ALSO REGIONS WHERE J.E>0. BUT THE POINT HERE IS THAT FORCE BALANCE IN THE IONOSPHERE REQUIRES FIELD-ALIGNED CURRENTS THAT IN TURN CLOSE WITH PERPENDICULAR CURRENTS IN THE MAGNETOSPHERE. THE RESULTANT JXB FORCE BALANCES THE PLASMA THERMAL AND DYNAMIC PRESSURE FORCES. BASED ON THE DIFFERENT CONTRIBUTORS TO THE FORCE BALANCE IN THE MAGNETOSPHERE THE FIELD-ALIGNED CURRENT CLOSURE IN THE MAGNETOSPHERE MAY BE ASSOCIATED WITH THERMAL PRESSURE GRADIENTS FLOW BRAKING OR VORTICITY IN THE PLASMA FLOW. THE BASIC OBJECTIVE OF THE PROPOSED RESEARCH IS TO DETERMINE THE RELATIONSHIP BETWEEN THE VARIOUS FORCES AND ASSOCIATED CURRENTS IN THE COUPLED TIME-VARYING MAGNETOSPHERE-IONOSPHERE SYSTEM. THE PROPOSED RESEARCH USES A COMBINATION OF DATA AND SIMULATIONS. DATA FROM THE LOW EARTH ORBITING FAST AURORAL SNAPSHOT (FAST) SMALL EXPLORER PROVIDE INFORMATION ON THE FIELD-ALIGNED CURRENTS AND THE ASSOCIATED PARTICLE DISTRIBUTIONS ABOVE THE IONOSPHERE. THE LATTER CAN BE USED TO CONSTRAIN WHERE THE FIELD-LINES PASSING THROUGH THE FAST SPACECRAFT MAP TO IN THE MAGNETOSPHERE. FOR EXAMPLE THE PRESENCE OF A DOUBLE LOSS-CONE FEATURE IN THE IONS SUGGESTS THAT THE FIELD LINES MAP TO THE INNER MAGNETOSPHERE WHERE PITCH-ANGLE SCATTERING IS REDUCED. IN SITU OBSERVATIONS FROM THE THEMIS SPACECRAFT CAN FURTHER CONSTRAIN THE MAPPING. WE WILL ALSO MAKE USE OF GROUND-BASED RESOURCES SUCH AS ALL SKY IMAGERS (ASIS) AND MAGNETOMETERS. MAGNETOMETER MEASUREMENTS CAN BE USED TO CREATE EQUIVALENT CURRENT SYSTEM MAPS TO PLACE THE MORE LOCAL FAST MEASUREMENTS INTO A GLOBAL CONTEXT. FINALLY WE WILL MAKE USE OF NUMERICAL SIMULATIONS TO GUIDE US IN OUR INTERPRETATION OF THE IN SITU OBSERVATIONS AND ALLOW US TO DETERMINE THE RELATIVE IMPORTANCE OF FLOW SHEAR FLOW BRAKING OR PRESSURE GRADIENTS. THE PROPOSED RESEARCH ADDRESSES TWO SCIENCE GOALS AS GIVEN IN THE HELIOPHYSICS DECADAL SURVEY: (1) DETERMINE THE DYNAMICS AND COUPLING OF THE EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR TERRESTRIAL INPUTS; AND (2) DISCOVER AND CHARACTERIZE FUNDAMENTAL PROCESSES THAT OCCUR BOTH WITHIN THE HELIOSPHERE AND THROUGHOUT THE UNIVERSE.