MAGNETIC RECONNECTION A PHENOMENON ASSOCIATED WITH BREAKING AND MENDING OF THE MAGNETIC FIELD LINES CONVERTS THAT ENERGY INTO THE THERMAL AND KINETIC ENERGY OF THE SURROUNDING PARTICLES. UNDERSTANDING MAGNETIC RECONNECTION IS IMPORTANT FOR PLASMA CONFINEMENT IN LABORATORY MAGNETIC FUSION EXPERIMENTS AND FOR PARTICLE ENERGIZATION IN GLOBAL SCALE PHENOMENA SUCH AS SOLAR FLARES AND AURORAL SUBSTORMS. 3D MAGNETOHYDRODYNAMIC SIMULATIONS AND LARGE-SCALE OBSERVATIONS HAVE LONG SHOWN THE FORMATION OF RECONNECTION X-LINES IN THE EARTH S CROSS-TAIL CURRENT SHEET DURING MAGNETIC SUBSTORMS AND STORMS. IN CONTRAST 2D KINETIC SIMULATIONS SHOW THAT MANY X-LINES FORM IN THINNED CURRENT SHEETS TO FORM MAGNETIC ISLANDS I.E. MAGNETIC ISLANDS OR FLUX ROPES IN THREE-DIMENSIONAL SPACE BETWEEN ELECTRON AND ION INERTIAL SCALES. AS RECONNECTION CONTINUES AT THE X-LINES NEIGHBORING MAGNETIC ISLANDS ARE PUSHED TOGETHER AND MERGE VIA RECONNECTION TO FORM LARGER ONES. THIS PROCESS IS TERMED COALESCENCE AND AS IT REPEATS LARGER AND LARGER SCALE ISLANDS ARE FORMED. AT THE DAYSIDE MAGNETOPAUSE AND IN THE CROSS-TAIL CURRENT SHEET FTES AND PLASMOIDS RESPECTIVELY ARE BELIEVED TO FORM DUE TO THIS PROCESS AND EVOLVE INTO LARGER STRUCTURES OVER TIME. THE RESEARCH TO BE SUPPORTED BY THIS UNSOLICITED PROPOSAL WILL ANALYZE THE HIGH SPATIAL AND TEMPORAL RESOLUTION PLASMA AND FIELDS MEASUREMENTS COLLECTED BY THE MAGNETOSPHERIC MULTISCALE (MMS) MISSION TO DETERMINE THE PHYSICAL PROPERTIES OF SUB-ION-SCALE FLUX ROPES IN THE CROSS-TAIL CURRENT SHEET AND THE MAGNETOPAUSE AND THE ROLE OF COALESCENCE IN THEIR GROWTH. OUR APPROACH IS TO USE A COMBINATION OF SINGLE- AND MULTI-SPACECRAFT DATA ANALYSIS TECHNIQUES TO INVESTIGATE THE CURRENTS SHEETS AND THE EMBEDDED X-LINES (E.G. MINIMUM VARIANCE AND WALEN ANALYSIS) AND THE STRUCTURE AND STRESS BALANCE IN ION-SCALE MAGNETIC FLUX ROPES (E.G. FORCE-FREE MODELING FITTING AND GRAD-SHAFRANOV RECONSTRUCTION). COMPARISONS WILL BE MADE AGAINST PUBLISHED PARTICLE-IN-CELL AND HYBRID SIMULATIONS TO DETERMINE THE PROPERTIES AND TIME-SCALES OF THE COALESCENCE PROCESS AND TO COMPARE AND CONTRAST HOW THE PROCESS OPERATES AT THE MAGNETOPAUSE AND IN THE TAIL. THE MMS CHARGED PARTICLES MEASUREMENTS PROVIDE THE ULTRA-HIGH TIME RESOLUTION DYNAMIC ENERGY SPECTRA PITCH ANGLE DISTRIBUTIONS AND FULL PARTICLE DISTRIBUTIONS AT SUFFICIENTLY HIGH-TIME RESOLUTION TO STUDY THE INTERNAL STRESS BALANCE BETWEEN PRESSURE GRADIENTS AND J X B WITHIN FLUX ROPES AS WELL AS BALANCING ANY EXTERNAL FORCES.