THE LACK OF DATA AT HIGH ENOUGH SPATIO-TEMPORAL SCALES HAS BEEN AN OBVIOUS HANDICAP FOR QUANTIFYING THE ROLE OF SALINITY IN INTRASEASONAL VARIABILITY AND HAS GREATLY INHIBITED THE ATTEMPTS TO QUANTIFY ITS ROLE ON MJO OR OTHER EXTENDED-RANGE PREDICTIONS. THE UNPRECEDENTED SSS SATELLITE OBSERVATIONS TOGETHER WITH IN SITU SALINITY OBSERVATIONS NOW OFFER A UNIQUE OPPORTUNITY TO TACKLE THIS IMPORTANT ISSUE. IN THIS PROPOSAL WE WILL PRODUCE OUR OWN HIGH-QUALITY SEA SURFACE SALINITY (SSS) PRODUCTS BY BLENDING THE INFORMATION DERIVED FROM IN SITU MEASUREMENTS WITH THE NASA AQUARIUS AND ESA SMOS SATELLITE OBSERVATIONS. FOR THE PURPOSE OF INTRASEASONAL APPLICATION WE WILL DEVELOP THE PRODUCTS AT SUB-MONTHLY TIMESCALES (10 DAYS 5 DAYS AND DAILY). FURTHER BASED ON THE SSS PRODUCTS AND A STATE-OF-THE-ART OPERATIONAL CLIMATE MODEL WE WILL CONDUCT EXPERIMENTS TO FOCUS ON TWO MAIN SCIENTIFIC QUESTIONS: (1) HOW/WHERE DOES THE SSS PLAY A VITAL ROLE IN UPPER OCEAN STRATIFICATION AND SST VARIABILITY IN THE TROPICAL OCEANS AND HOW DOES IT INFLUENCE MJO EVOLUTION? (2) HOW CAN WE OPTIMALLY EMPLOY SSS OBSERVATIONS TO FURTHER IMPROVE MJO PREDICTION? TO ADDRESS QUESTION (1) WE WILL DETERMINE HOW SIMULATIONS OF THE INTRASEASONAL SST VARIABILITY AND MJO ARE SENSITIVE TO SSS IN DIFFERENT BASINS. THE REGIONS IDENTIFIED AS IMPORTANT CAN THEN BE A FOCUS FOR FURTHER PROCESS STUDIES AND SENSITIVITY EXPERIMENTS AND ALSO GUIDE OBSERVATIONAL STRATEGIES. FOR QUESTION (2) WE WILL COMPARE A SET OF MJO PREDICTION EXPERIMENTS BY APPLYING SSS OBSERVATIONS IN DIFFERENT WAYS: SKIN VS. BULK SURFACE SALINITY HIGH (1M) VS. STANDARD (10M) VERTICAL RESOLUTION IN THE OCEAN MODEL FULL VS. ANOMALY INITIALIZATIONS AND DIFFERENT FREQUENCY OF SSS PRODUCTS. IN EACH OF THE SIMULATIONS AND PREDICTIONS RELEVANT OCEAN DYNAMIC AND AIR-SEA INTERACTION PROCESSES WILL ALSO BE ANALYZED IN DETAILS TO QUANTIFY THE ROLE OF SSS IN MJO PREDICTION.