WATER VAPOR MAKES THE SINGLE MOST IMPORTANT CONTRIBUTION TO THE RADIATIVE FORCING THAT IS WARMING THE CLIMATE AND GLOBAL TEMPERATURES ARE SENSITIVE IN PARTICULAR TO CHANGES OF WATER VAPOR IN THE UPPER TROPOSPHERE AND LOWER STRATOSPHERE (UT/LS). OUR CONFIDENCE IN THE LATTER RESULT IS UNDERPINNED BY NEARLY THREE DECADES OF SATELLITE WATER VAPOR MEASUREMENTS AND THEIR MERGING INTO A SINGLE CONTINUOUS RECORD OF STRATOSPHERIC WATER VAPOR OVER THE GLOBE. THIS ACHIEVEMENT IS IN LARGE PARTS DUE TO THE REMARKABLE ACCURACY STABILITY AND LONGEVITY OF THE MLS INSTRUMENT ON NASA'S EOS AURA SATELLITE AND TO A NETWORK OF BALLOON-BORNE FROST POINT MEASUREMENTS THAT HAVE BEEN PROVIDING VALIDATION FOR SATELLITE WATER VAPOR MEASUREMENTS AS WELL AS PROVIDING ROBUST ESTIMATES OF STRATOSPHERIC WATER VAPOR TRENDS. HOWEVER WITH AURA NOW WELL INTO ITS EXTENDED MISSION AND WITH NO SUCCESSOR TO MLS CURRENTLY ON THE LAUNCH HORIZON THE COMING TERMINATION OF AURA WILL LIKELY RESULT IN AN EXTENDED GAP IN THE GLOBAL WATER VAPOR RECORD POSSI BLY YEARS IN LENGTH. SAGE-III ON ISS WHICH IS SCHEDULED FOR LAUNCH IN LATE 2016 IS CURRENTLY THE ONLY SPACE-BASED SYSTEM SET TO PROVIDE PROFILING OF STRATOSPHERIC WATER VAPOR DURING THIS 'WATER GAP'. WHILE OTHER SYSTEMS MAY BE DEVELOPED TO AUGMENT SAGE-III IT APPEARS VERY LIKELY THAT MONITORING OF UT/LS WATER VAPOR FROM SPACE WILL BECOME EXTREMELY LIMITED AT SOME POINT IN THE COMING YEARS. THE SUCCESS OF THIS STRATEGY OF LIMITED SPACE-BASED MONITORING OF WATER VAPOR WILL RELY HEAVILY ON NASA S SUPPORT OF SUBORBITAL MEASUREMENT PROGRAMS TO MONITOR WATER VAPOR IN THE UT/LS IN PARTICULAR A SMALL GROUP OF SITES IN THE TROPICS AND MIDDLE LATITUDES THAT PROFILE WATER VAPOR REGULARLY WITH BALLOON BORNE FROST POINT INSTRUMENTS. IT IS THUS CRITICAL THAT NASA CONTINUE TO SUPPORT WATER VAPOR MEASUREMENTS AT THESE SITES. THESE WILL FULFILL THE NEED BOTH FOR MONITORING OF THE GLOBAL STRATOSPHERIC WATER VAPOR AND FOR VALIDATION OF PROFILES FROM SAGE-ILL WATER VAPOR AND OTHER SPACE-BASED SYSTEMS. RECOGNIZING THE PARAMOUNT IMPORTANCE OF WATER VAPOR IN THE CLIMATE SYSTEM AND THE GREAT VALUE OF ACCURATE YET RELATIVELY INEXPENSIVE BALLOON-BORNE FROST POINT HYGROMETERS FOR BOTH ITS MONITORING AND VALIDATION IN THE UT/LS WE INITIATED THE TICOSONDE/SHADOZ WATER VAPOR AND OZONE PROJECT IN COSTA RICA IN 2005. OVER THE SUBSEQUENT 11 YEARS WE HAVE MADE OVER 200 WATER VAPOR SOUNDINGS MAKING IT THE ONLY CONTINUOUS RECORD OF IN SITU WATER VAPOR MEASUREMENTS IN THE TROPICS. OVER THIS SAME PERIOD TICOSONDE HAS BEEN A KEY MEMBER OF THE SHADOZ STATION NETWORK CONTRIBUTING OVER 500 OZONE PROFILES. OUR OVERALL OBJECTIVE IN THIS PROPOSAL IS TO BUILD UPON THIS RECORD IN ORDER TO FULFILL NASA'S NEED TO NOT ONLY SUPPORT WATER VAPOR MONITORING BUT ALSO TO PROVIDE SUFFICIENT WATER VAPOR AND OZONE DATA FOR VALIDATION OF THE SAGE-III ISS AND OTHER SPACE-BASED MEASUREMENTS OF THESE TRACE SPECIES IN THE UT/LS. SAN JOSE COSTA RICA IS THE ONLY FROST POINT SITE LOCATED WITHIN THE DEEP TROPICS MAKING REGULAR MEASUREMENTS OF WATER VAPOR INTO THE LOWER STRATOSPHERE; THUS IT ALONE WI LL BE AB LE TO MONITOR TROPICAL WATER VAPOR DURING THE COMING 'WATER GAP' AND TO SUPPORT VALIDATION OF THE SAGE-ILL ISS INSTRUMENT. THE MEASUREMENT PROGRAM IS IN VERY RELIABLE HANDS: OVER THE PAST 5 YEARS THE PROJECT HAS HAVE ESTABLISHED A TOP-NOTCH LAUNCH TEAM AT THE UNIVERSITY OF COSTA RICA AND CO-I YOMEL IS THE DEVELOPER OF THE CFH INSTRUMENT AND AS SUCH HAS INTIMATE KNOWLEDGE OF ITS PERFORMANCE. TO ACHIEVE OUR PRIMARY OBJECTIVE TO SUPPORT MONITORING OF UT/LS WATER VAPOR AND TO PROVIDE DATA FOR VALIDATION OF SPACE-BASED PROFILES WE WILL CARRY OUT THE FOLLOWING ACTIVITIES: REGULAR IN SITU BALLOON-BORNE PROFILING OF WATER VAPOR AND OZONE AND TO THE LOWER AND MIDDLE STRATOSPHERE - WE WILL CONTINUE OUR PRESENT PROGRAM OF WEEKLY LAUNCHES IN COSTA RICA OF ELECTROCHEMICAL CONCENTRATION CELL (ECC) OZONE SONDES AUGMENTED ONCE MONTHLY WITH THE CRYOGENIC FROST POINT HYGRO