THE PROPOSED RESEARCH AIMS TO INCREASE OUR UNDERSTANDING OF WHAT DRIVES THE GLOBAL WATER CYCLE IN CLIMATE MODELS AND OBSERVATIONS. THE WORK HAS TWO SPECIFIC AIMS: A) TO IDENTIFY LIKELY LEADING MECHANISMS BEHIND THE SPREAD IN GLOBAL MEAN PRECIPITATION ACROSS CLIMATE MODELS AND B) TO DETERMINE WHY MANY CLIMATE MODELS APPEAR TO OVERESTIMATE THE PRESENT-DAY GLOBAL MEAN PRECIPITATION RATE. THE STUDY WILL EMPLOY OUTPUT FROM CURRENT STATE-OF-THE-ART CLIMATE MODELS NASA SATELLITE RETRIEVALS OF ATMOSPHERIC VARIABLES AND NASA'S GODDARD INSTITUTE OF SPACE STUDIES E3 (GISS-E3) CLIMATE MODEL. TWO SEPARATE FRAMEWORKS HELP US UNDERSTAND HOW HEAVILY IT PRECIPITATES: CLOUD-SCALE PROCESSES DRIVE LOCAL-SCALE PRECIPITATION AND AN ATMOSPHERIC ENERGETIC CONSTRAINT HELPS EXPLAIN GLOBAL-MEAN PRECIPITATION RATES BY TYING PRECIPITATION RATES TO LATENT HEAT FLUXES. DESPITE THEIR SEPARATE CONTRIBUTIONS TO OUR UNDERSTANDING OF THE GLOBAL WATER CYCLE THEY HAVE RARELY BEEN COMBINED IN PREVIOUS STUDIES. THE PROPOSED STUDY ATTEMPTS TO BRIDGE THESE TWO DIFFERENT FRAMEWORKS TO UNDERSTAND WHAT DETERMINES THE GLOBAL MEAN PRECIPITATION RATE IN CURRENT STATE-OF-THE-ART CLIMATE MODELS. WHEN WE EXAMINE THE PRESENT-DAY GLOBAL MEAN PRECIPITATION RATES AS SIMULATED BY CLIMATE MODELS PARTICIPATING IN THE FIFTH COUPLED MODEL INTERCOMPARISON PROJECT (CMIP5) WE FIND A 14% SPREAD IN GLOBAL MEAN PRECIPITATION RATE ACROSS MODELS EVEN WHEN THE MODELS ARE ALL FORCED WITH THE SAME SEA SURFACE TEMPERATURE AND ATMOSPHERIC FORCING AGENTS. BASED ON PRELIMINARY ANALYSES WE FIND THAT VARIATIONS IN THE LONGWAVE COOLING AND SENSIBLE HEAT FLUX INTO THE ATMOSPHERE EXPLAIN A MAJORITY OF THE VARIANCE AND WE HYPOTHESIZE THAT A SUBSTANTIAL AMOUNT OF THE INTERMODEL SPREAD IN GLOBAL MEAN PRECIPITATION CAN BE EXPLAINED BY DIFFERENCES IN MODEL PHYSICS THAT DETERMINE TWO MECHANISMS: THE PRECIPITATION EFFICIENCY AND VERTICAL MIXING STRENGTH. METRICS WILL BE CONSTRUCTED TO QUANTIFY THE STRENGTH OF THESE TWO MECHANISMS TO TEST THIS HYPOTHESIS. WE ALSO HYPOTHESIZE THAT THE STRENGTH OF THE TWO MECHANISMS EXPLAINS THE BIAS THAT MANY MODELS HAVE IN OVERESTIMATING THE GLOBAL MEAN PRECIPITATION. WE WILL TEST THIS HYPOTHESIS BY COMPARING THE METRICS OF THE TWO MECHANISMS WHICH WE CALCULATE FROM THE CMIP5 MODELS AND FROM NASA SATELLITE AND REANALYSIS PRODUCTS. THIS WILL GUIDE EXPERIMENTS WITH NASA'S GISS E3 CLIMATE MODEL. USING THE METRICS VARIOUS CONFIGURATIONS OF NASA'S GISS E3 MODEL WILL BE USED TO CONCLUSIVELY TEST WHETHER THE HYPOTHESIZED MECHANISMS CAN EXPLAIN DIFFERENCES IN PRECIPITATION RATES AT LEAST WITHIN THE CONFINES OF A SINGLE-MODEL FRAMEWORK. FINALLY WE WILL TEST WHETHER THE MODEL BIASES IN THE GLOBAL MEAN PRECIPITATION RATE ARE IMPROVED IF WE CONFIGURE THE LOCAL-SCALE PROCESS PARAMETERIZATIONS TO MATCH THE OBSERVED STRENGTH OF THE METRICS. THE FINDINGS FROM THIS INVESTIGATION WILL ADVANCE OUR UNDERSTANDING OF THE RELATIONSHIP BETWEEN LOCAL-SCALE PHYSICS AND GLOBAL-SCALE ENERGY CONSTRAINTS AND HELP PROVIDE A LARGE-SCALE MECHANISTIC UNDERSTANDING OF WHAT DRIVES THE OBSERVABLE WATER CYCLE. THE RESULTS WILL ALSO IDENTIFY WHAT MECHANISMS NEED TO BE BETTER UNDERSTOOD REPRESENTED IN CLIMATE MODELS AND OBSERVED IF WE WISH TO GAIN A FUNDAMENTAL UNDERSTANDING OF WHAT DRIVES THE GLOBAL WATER CYCLE IN THE FUTURE.