MOTIVATION: NASA DE-1/RIMS OBSERVATIONS HAVE REVEALED THAT THE DENSITY PROFILE OF HEAVY COLD IONS IS DISTINCTLY DIFFERENT FROM THAT OF LIGHT IONS (H+ AND HE+) [E.G. HORWITZ ET AL. 1984; ROBERTS ET AL. 1988]: O+ AND O++ DENSITIES ARE ENHANCED IN THE VICINITY OF THE PLASMAPAUSE (50%) DURING OR AFTER STORMS WHILE NOMINAL O+ CONCENTRATIONS ARE 1% OR LESS INSIDE THE PLASMASPHERE. ONE MIGHT SUSPECT THAT HEAVY IONS ARE NOT SUPPLIED VIA THE SAME REFILLING PROCESS FROM THE IONOSPHERE [GALLAGHER AND COMFORT 2016]. THE UNDERLYING PHYSICAL PROCESSES THAT COULD EXPLAIN THE OBSERVED PROFILES HAVE STILL NOT BEEN COMPLETELY KNOWN ALTHOUGH TWO HYPOTHESES HAVE BEEN PROPOSED: GEOMAGNETIC MASS SPECTROMETER PROCESS [LOCKWOOD ET AL. 1985; HORWITZ AND LOCKWOOD 1985; WAITE ET AL. 1985] AND IONOSPHERIC HEATING PROCESS [HORWITZ ET AL. 1986]. THE DISTRIBUTION OF THE HEAVY IONS IN TIME AND SPACE IS NOT YET FULLY UNDERSTOOD: FOR EXAMPLE WHETHER OR NOT THE OXYGEN TORUS IS ACTUALLY A TORUS AND WHETHER OR NOT HAS THE OXYGEN ION TORUS BEEN CONFUSED WITH THE WARM (10--100EV) PLASMA CLOAK [CHAPPELL ET AL. 2008]. THIS IS IMPORTANT BECAUSE COMPOSITION IMPACTS THE GROWTH OF ELECTROMAGNETIC ION CYCLOTRON (EMIC) WAVES THAT SCATTER RADIATION BELT ELECTRONS. FURTHERMORE MASS LOADING ALTERS THE ALFVEN SPEED AT WHICH ULTRALOWFREQUENCY (ULF) WAVES PROPAGATE. IN ADDITION THE PLASMASPHERIC MASS DENSITY MAY AFFECT THE DAYSIDE MAGNETIC RECONNECTION BY EXERTING LARGE INERTIA. SCIENCE GOALS AND OBJECTIVES: THE OVERALL OBJECTIVE OF THIS PROJECT IS TO EXAMINE THE VARIOUS UNDERLYING PHYSICAL PROCESSES THAT CONTROL THE COLD ION COMPOSITION IN THE PLASMASPHERE. THE PROPOSAL WILL ADDRESS 2 SPECIFIC SCIENCE QUESTIONS: (1) WHAT ARE THE PHYSICAL PROCESSES THAT CAN EXPLAIN THE COLD HEAVY ION COMPOSITION IN PLASMASPHERE; (2) AND WHAT ARE THEIR RELATIVE ROLES AND TIME SCALES ON INDIVIDUAL STORM EVENTS? METHODOLOGY: (1) NUMERICAL SIMULATIONS USING THE FULLY COUPLED WHOLE ATMOSPHERE MODEL (WAM) AND THE IONOSPHERE PLASMASPHERE MODEL (IPE) TO QUANTIFY THE PLASMASPHERIC COLD ION COMPOSITION; (2) ANALYSIS OF RBSP HOPE AND TWINS ENA DATA TO QUANTIFY THE ENERGY INPUT TO THE THERMAL PLASMAS DUE TO COULOMB COLLISIONAL DEGRADATION OF HOT IONS IN THE INNER MAGNETOSPHERE DURING SELECTED STORMS WITH THE HELP OF THE COMPREHENSIVE INNER MAGNETOSPHERE-IONOSPHERE (CIMI) MODEL; (3) INCLUSION OF RING CURRENT HEATING INTO THE WAM-IPE TO EVALUATE THE PLASMASPHERIC ION COMPOSITION; (4) VALIDATING OF MODELED ION COMPOSITION AGAINST RBSP OBSERVATIONS; (5) COMPREHENSIVE SENSITIVITY STUDIES TO UNDERSTAND THE VARIOUS EFFECTS ON PLASMASPHERIC COLD ION COMPOSITIONS. RELEVANCE: UNDERSTANDING THE EVOLUTION OF THE COLD ION COMPOSITION IN THE PLASMASPHERE IS CRITICAL IN UNDERSTANDING THE RADIATION BELT FLUX SUCH AS BY WAVE-PARTICLE INTERACTIONS WHICH IS A MAIN SCIENCE GOAL OF THE NASA RBSP MISSION. COMBINED USE OF RBSP AND NASA TWINS MEASUREMENTS WILL HELP US ENHANCE OUR UNDERSTANDING OF THE EVOLUTION OF THE MAGNETOSPHERIC STRUCTURE PROCESSES AND ION DYNAMICS WHICH IS THE MAIN SCIENCE GOAL OF THE NASA TWINS MISSION. THE PROJECT IS RELEVANT TO ONE OF THE TOP FOUR SCIENTIFIC GOALS LISTED IN THE NASA HELIOPHYSICS DECADAL SURVEY DETERMINE THE DYNAMICS AND COUPLING OF EARTH S MAGNETOSPHERE IONOSPHERE AND ATMOSPHERE AND THEIR RESPONSE TO SOLAR AND TERRESTRIAL INPUTS.