THE AMAZON IS A HOME FOR MORE THAN 34 MILLION PEOPLE AND A PARADISE OF A HUGE VARIETY OF PLANTS AND ANIMALS. THE AMAZON RAINFOREST PLAYS A VITAL ROLE IN THE GLOBAL ECOSYSTEM AND CLIMATE CHANGE REGULATING TEMPERATURES AND STORING VAST QUANTITIES OF CARBON DIOXIDE. A QUESTION WE NEED TO THUS ASK IS: WHAT IS THE LIMITING FACTOR THAT CONTROLS PLANT GROWTH OVER AMAZONIA: LIGHT OR WATER? CONSIDERABLE EVIDENCE DEMONSTRATES THAT SUNLIGHT INDEED DRIVES AMAZON FOREST GROWTH ALTHOUGH WATER DEFICIT COULD BE A LIMITING FACTOR DURING SEVERE DROUGHT SEASONS. ATMOSPHERIC AEROSOLS AND CLOUDS IMPACT SOLAR RADIATION REACHING PLANT CANOPY NOT ONLY IN TOTAL AMOUNT BUT ALSO IN THE RATIO OF DIRECT AND DIFFUSE RADIATION THE LATTER ENHANCING PLANT LIGHT USE EFFICIENCY. YET ALTHOUGH PRESENCE OF AEROSOLS AND CLOUDS HAS A SIGNIFICANT INFLUENCE ON FOREST PRODUCTIVITY VIA THEIR IMPACT ON RADIATION FIELDS A SYSTEMATICAL ASSESSMENT OF SUCH AN INFLUENCE ON MULTI-SEASON AND MULTIYEAR SCALES OVER THE AMAZON BASIN HAS NOT YET BEEN EXPLORED. WE PROPOSE A THREE-YEAR PROJECT TO FILL THIS GAP BY ADDRESSING THE FOLLOWING QUESTIONS: 1. HOW DO ATMOSPHERIC AEROSOLS AND CLOUDS IMPACT SOLAR RADIATION AND THUS IMPACT VEGETATION OVER THE AMAZON BASIN? 2. WHAT IS THE SEASONAL DEPENDENCE (DRY WET AND TRANSITION) OF SUCH A RELATIONSHIP AMONG AEROSOL/CLOUD RADIATION TEMPERATURE SOIL MOISTURE AND FOREST PRODUCTIVITY? 3. DOES NATURAL YEAR-TO-YEAR VARIATION IN LIGHT INTENSITY OWING TO CLOUD COVER (TREND OR EXTREME EL NI O EVENT) DOMINATE THE INTERANNUAL VARIATION OF PHOTOSYNTHESIS AND CARBON UPTAKE OVER THE AMAZON? WE WILL SYNERGISTICALLY USE VARIOUS OBSERVATIONS AND THE GEOS-5 AGCM MODEL IN THIS STUDY. FIRST WE WILL ANALYZE VARIOUS SATELLITE PRODUCTS (I.E. AEROSOL CLOUD RADIATION PRECIPITATION NDVI AND SIF) OVER 1997-2017 TO REVEAL THEIR MAGNITUDE TREND AND CORRELATION ON MONTHLY SEASONAL (DRY WET AND TRANSITION) AND ANNUAL BASIS. THE ANALYSES WILL BE PERFORMED FURTHER BY SEPARATING CLIMATE BACKGROUNDS OF NORMAL EL NI O AND LA NI A YEARS. SECOND WE WILL CONDUCT A GLOBAL BASELINE SIMULATION WITH GEOS-5 FOR THE SAME PERIOD. THE GEOS-5 MODEL WILL INCLUDE A CAPABILITY OF COUPLING AEROSOL-CLOUD-RADIATION-VEGETATION PROCESSES TO ALLOW DYNAMIC FEEDBACK OF AEROSOL AND CLOUD ON RADIATION AND VEGETATION FIELDS. WE WILL USE OBSERVATIONS FROM GROUND-BASED AIRCRAFT AND SATELLITE TO EVALUATE THE MODEL FOCUSING ON THE AMAZON REGION AND USE THE EVALUATED MODEL TO CONFIRM THE SATELLITE FINDINGS OBTAINED IN STEP ONE. THIRD WE WILL CONDUCT A SERIES OF SENSITIVITY EXPERIMENTS USING THE GEOS-5 MODEL BY PERTURBING: 1) THE AMAZON BIOMASS BURNING EMISSION TO EXPLORE A BETTER STRATEGY OF CONTROLLING THE AMAZON FIRES FROM A PERSPECTIVE OF PRESERVING FOREST CARBON; AND 2) CLOUDINESS TO GAIN INSIGHT INTO THE IMPACT OF POTENTIAL FUTURE CLOUD CHANGE ON THE AMAZON FOREST PRODUCTIVITY. OUR PROPOSED STUDY DIRECTLY ADDRESSES THE ACMAP S RESEARCH THEMES HOW DOES ATMOSPHERIC COMPOSITION RESPOND TO AND AFFECT GLOBAL ENVIRONMENTAL CHANGE? AND WHAT TRENDS IN ATMOSPHERIC COMPOSITION AND SOLAR RADIATION ARE DRIVING GLOBAL CLIMATE?