SCIENTIFIC GOALS CASSINI RADAR AND NEAR-IR CAPABILITIES REVEAL TITAN'S LAKES RAIN AND CLOUDS WHICH FORM PART OF A METHANE CYCLE SIMILAR TO THE HYDROLOGICAL CYCLE ON EARTH. MEASURED TEMPERATURE PROFILES NOW EXTEND FROM THE EQUATOR TO WITHIN 10 OF THE POLES OVER A RANGE OF SEASONS. YET STILL LITTLE IS KNOWN ABOUT TITAN'S CLIMATE AND ITS SEASONAL AND LATITUDINAL VARIATIONS LARGELY BECAUSE THE METHANE PROFILE IN TITAN'S TROPOSPHERE HAS BEEN MEASURED ONLY ONCE AT THE HUYGENS PROBE LANDING SITE (-10 LATITUDE 191W LONGITUDE) ON 14 JANUARY 2005 AND ONCE WITH KECK OBSERVATIONS OF THE METHANE ABUNDANCE ALONG A NORTH-SOUTH STRIP. THE CASSINI MISSION CANNOT MEASURE THE TROPOSPHERIC METHANE ABUNDANCE. IT LACKS HIGH SPECTRAL RESOLUTION CAPABILITIES NEEDED TO RESOLVE WEAK NON-SATURATED LINES. GROUND BASED MEASUREMENTS DO HAVE THIS CAPABILITY. METHODOLOGYTHE PROPOSED INVESTIGATION ANALYSES EXISTING KECK/NIRSPEC SPECTRAL IMAGES RECORDED IN 2006 2012 AND 2015 AND SCHEDULED OBSERVATIONS IN 2017 THAT WILL BE AVAILABLE BEFORE THE BEGINNING OF THIS PROJECT. WITH A RESOLVING POWER (R=25 000) 100 TIMES GREATER THAN CASSINI CAPABILITIES KECK OBSERVATIONS ISOLATE WEAK LINES SENSITIVE TO THE METHANE ABUNDANCE BELOW 10 KM ALTITUDE WHERE MOST OF THE METHANE RESIDES. THE 1.46-1.70 MICRON SPECTRA SPANNING NEARLY HALF A TITAN YEAR ENABLES MEASUREMENTS OF TROPOSPHERIC METHANE AND ITS CHANGES WITH LATITUDE AND SEASON. THE KECK DATA WITH A SPATIAL RESOLUTION EQUIVALENT TO 20 PIXELS ACROSS TITAN'S DISK SAMPLES THE NORTH TO SOUTH CHANGES IN THE METHANE ABUNDANCE FROM 2006 TO 2017. AMONG THE REGIONS TARGETED IS THE HUYGENS LANDING SITE IN 2015 (TEN YEARS AFTER THE LANDING) AND THE NORTH POLE BOTH OFF AND ON THE POLAR LAKES. THE DERIVED METHANE VALUES ARE INTERPRETED WITH THERMODYNAMIC MODELS TO DETERMINE THE STABILITY OF THE ATMOSPHERE WITH RESPECT TO CONVECTION WHICH TAKEN TOGETHER WITH CASSINI MEASUREMENTS OF THE TEMPERATURE AND WIND STRUCTURE PROBE THE PROCESSES UNDERLYING TITAN'S CLOUDS STORMS AND RAIN. THE LATITUDINAL VARIATIONS IN THE METHANE CONTENT WILL BE INTERPRETED WITH GENERAL CIRCULATION MODELS TO INVESTIGATE THE TRANSPORT OF METHANE BETWEEN THE SURFACE AND THE ATMOSPHERE AND FROM THE EQUATOR TO HIGH LATITUDES AND TO EXPLORE THE VARIABLE SEASONAL CLIMATIC CONDITIONS ACROSS TITAN'S GLOBE. LOCAL REGIONS OF ABNORMALLY HIGH METHANE AS INDICATED BY THE PRIOR 2014 KECK OBSERVATION (ADAMKOVICS ET AL. 2016) WILL BE STUDIED TO DETERMINE WHETHER THESE METHANE-RICH REGIONS ARE IMPERVIOUS TO SEASONAL CHANGES AND CONNECTED TO THE SURFACE INDICATIVE OF METHANE CRYOGENIC OUTGASSING OR SEEPAGE OF METHANE FROM SUBSURFACE RESERVOIRS. THIS ANALYSIS INVESTIGATES THE HISTORY OF TITAN S ATMOSPHERE AS THE CURRENT METHANE INVENTORY UNLESS SOMEHOW RESUPPLIED WILL BE IRREVERSIBLY EXHAUSTED IN 20 MILLION YEARS THEREBY SHRINKING THE ATMOSPHERE AND PURGING IT OF ORGANIC MATERIAL. RELEVANCE TO SOLAR SYSTEMS WORKINGS RESEARCHTHIS INVESTIGATION INVOLVES RESEARCH INTO ATMOSPHERIC CLIMATOLOGICAL AND GEOPHYSICAL PROCESSES OCCURRING ON PLANETARY BODIES AND ADDRESSES PHYSICAL PROCESSES THAT AFFECT SURFACES AND ATMOSPHERES. PLEASE NOTE THAT THIS PROJECT INVOLVES THE ANALYSIS OF EXISTING GROUND-BASED DATA AND IS THEREFORE NOT ELIGIBLE FOR FUNDING BY THE DATA ANALYSIS OR CASSINI PROGRAMS NOR THE SOLAR SYSTEM OBSERVATIONS PROGRAM.