DUE TO THEIR STRONG WINDS AND INTENSE RAINFALL TROPICAL CYCLONES CAN HAVE A PROFOUND IMPACT ON THE THERMAL AND SALINITY STRUCTURE OF THE UPPER OCEAN. HOWEVER RECENT RESEARCH HAS ALSO EMPHASIZED THE IMPACT OF UPPER-OCEAN SALINITY STRATIFICATION ON THE TROPICAL CYCLONE-INDUCED SURFACE COOLING (MCPHADDEN ET AL. 2009; NEETU ET AL. 2012; ANDROULIDAKIS ET AL. 2016). THESE STUDIES SUGGEST THAT FRESHENING OF THE OCEAN SURFACE INDUCES SALINITY BARRIERS THAT INHIBIT VERTICAL MIXING OF THE UPPER OCEAN. THE REDUCED MIXING IN TURN ALLOWS WARMER SURFACE WATERS TO PERSIST RESULTING IN MORE INTENSE TROPICAL CYCLONES. HOWEVER OTHER STUDIES HAVE CHALLENGED THIS CONCLUSION CLAIMING THAT THE COOLING INHIBITION EFFECT OF SALINITY STRATIFICATION AND BARRIER LAYERS IS SMALL AND THAT REGIONAL VARIATIONS IN THERMAL STRATIFICATION ARE THE MAIN FACTOR CONTROLLING THE AMPLITUDE OF TROPICAL CYCLONE INDUCED COOLING. GIVEN THEIR SUBSTANTIAL SOCIETAL AND ECONOMIC IMPACT DEVELOPING A BETTER UNDERSTANDING OF THE MECHANISMS THAT CONTROL TROPICAL CYCLONE INTENSIFICATION IS OF OBVIOUS IMPORTANCE. IN THIS PROPOSAL WE SEEK TO BETTER UNDERSTAND THE INTERACTIONS AND POTENTIAL FEEDBACKS BETWEEN TROPICAL CYCLONES (TCS) AND SURFACE SALINITY THROUGH A COMBINED ANALYSIS OF SATELLITE AND IN-SITU OBSERVATIONS TC-RESOLVING GLOBAL MODEL SIMULATIONS AND SENSITIVITY STUDIES USING HIGH-RESOLUTION MODEL SIMULATIONS. IN PARTICULAR WE SEEK TO ANSWER THE FOLLOWING QUESTIONS: I) WHAT IS THE IMPACT OF TROPICAL CYCLONE RAINFALL AND WINDS ON OCEAN SURFACE SALINITY? II) TO WHAT EXTENT DOES HEAVY RAINFALL OR RUNOFF AFFECT BUOYANCY OF THE UPPER OCEAN IN WAYS THAT INFLUENCE TC INTENSIFICATION? III) WHAT IMPACT DO FRESHWATER SALINITY BARRIERS HAVE ON TROPICAL CYCLONE-INDUCED SURFACE COOLING AND SUBSEQUENT INTENSIFICATION? IV) ARE PERIODS OF INTENSE RAINFALL/RUNOFF AND ASSOCIATED SURFACE FRESHENING ASSOCIATED WITH INCREASE RISK OF FUTURE RAPID INTENSIFICATION? V) HOW CAN SATELLITE OBSERVATIONS BE BEST USED TO EVALUATE AND IMPROVE THE REPRESENTATION OF THESE PROCESSES IN GLOBAL MODELS? VI) CAN SURFACE SALINITY MEASUREMENTS IMPROVE INTENSITY FORECASTS? THE MAIN RESOURCE FOR THIS WORK WILL BE SATELLITE OBSERVATIONS OF SALINITY RAINFALL AND SURFACE WIND SPEED FROM NASAS AQUARIUS SATELLITE (2011-2015) AND NASAS SOIL MOISTURE ACTIVE-PASSIVE (SMAP) COMPLIMENTED BY OBSERVATIONS FROM THE EUROPEAN SPACE AGENCYS SOIL MOISTURE AND OCEAN SALINITY (SMOS) SATELLITE. ADDITIONAL INFORMATION ON THE VERTICAL STRUCTURE OF SALINITY AND TEMPERATURE IN THE UPPER OCEAN WILL COME FROM THE ARGO ARRAY OF PROFILING FLOATS AND FROM OCEAN ANALYSES OBTAINED FROM THE NOAA GFDL AND NASA GEOS IODAS OCEAN DATA ASSIMILATION SYSTEMS. SINCE THE LAUNCH OF AQUARIUS IN 2011 THERE HAVE BEEN OVER 500 TROPICAL CYCLONES GLOBALLY. WE PROPOSE TO CONSTRUCT STORM-CENTERED COMPOSITES OF ALL TCS FOR WHICH THERE ARE SALINITY OBSERVATIONS FROM ONE OF THE SATELLITES CONTRASTING THE SALINITY CONDITIONS BEFORE AND AFTER THE TC OVERPASS. THESE COMPOSITES WILL BE FURTHER STRATIFIED ACCORDING TO RAINFALL STORM INTENSITY AND SIZE TO QUANTIFY THE IMPORTANCE OF THESE FACTORS IN MODIFYING OCEAN SALINITY. THESE COMPOSITES WILL BE COMPARED TO GLOBAL MODEL SIMULATIONS FROM THE GFDL TC-PERMITTING COUPLED OCEAN-ATMOSPHERE AND IN REGIONAL MODEL DOWNSCALING SIMULATIONS. SENSITIVITY STUDIES WILL BE PERFORMED IN WHICH SURFACE SALINITY IS MODIFIED (E.G. SO IT DOES NOT RESPOND TO CHANGES IN TC-INDUCED ATMOSPHERIC FORCING OR ARTIFICIALLY ENHANCING SALINITY STRATIFICATION) TO EVALUATE THE IMPACT OF SALINITY CHANGES ON TC INDUCED MIXING AND SUBSEQUENT INTENSIFICATION. BY COMPLETING THESE TASKS THIS PROPOSAL WILL DIRECTLY SUPPORT OF THE PROGRAM GOALS OF EXPLOITING SATELLITE SALINITY MEASUREMENTS AND THEIR SYNERGISTIC USE WITH OTHER OBSERVATIONS TO INVESTIGATE SALINITY VARIABILITY PARTICULARLY NEAR-SURFACE SALINITY STRATIFICATION AND ITS LINKAGE THE ATMOSPHERIC HYDROLOGIC CYCLE