WE PROPOSE TO USE OBSERVATIONS FROM OCO-2 AND OCO-3 TO EVALUATE REGIONAL PERTURBATIONS TO THE CARBON CYCLE DUE TO ANOMALIES IN CLIMATE (E.G. HOT COLD WET DRY). WE WILL ANALYZE THE ENVIRONMENTAL FACTORS THAT DRIVE THOSE REGIONAL CHANGES AND THE EXTENT TO WHICH SOLAR-INDUCED FLUORESCENCE (SIF) AND NEAR.INFRARED REFLECTANCE OF VEGETATION (NIRV) CAN PREDICT THE CARBON CYCLE RESPONSE. WE WILL ALSO EVALUATE DIFFERENCES AMONG ESTIMATES OF THE CARBON CYCLE RESPONSE WITHIN AN ENSEMBLE OF STATE-OF-THE-ART TERRESTRIAL BIOSPHERE MODELS (TBMS) AND DIAGNOSE WHAT ENVIRONMENTAL FACTORS ARE LIKELY DRIVING DIFFERENCES AMONG THESE MODELS. EVEN SMALL VARIABILITY IN ENVIRONMENTAL OR METEOROLOGICAL CONDITIONS CAN YIELD LARGE REGIONAL PERTURBATIONS IN CO2 FLUXES. THESE FLUX PERTURBATIONS PROVIDE IMPORTANT CASE STUDIES TO UNDERSTAND KEY CONTROLS ON THE CURRENT CARBON CYCLE AND ARE A PREREQUISITE TO UNDERSTAND FUTURE CARBON-CLIMATE FEEDBACKS. EXISTING TBMS HOWEVER YIELD VERY DIFFERENT RESPONSES TO CLIMATE ANOMALIES AND DIFFER BY OVER A FACTOR OF FIVE IN THEIR RESPONSE TO DROUGHT HEAT COLD SPELLS AND EXTREME WET CONDITIONS. WE HYPOTHESIZE THAT DROUGHTS IN TROPICAL DRYLAND ECOSYSTEMS YIELD PERTURBATIONS TO CO2 FLUXES THAT ARE LARGER THAN FROM ANY OTHER CLIMATE ANOMALY. WITH THAT SAID WE HYPOTHESIZE THAT MOST TBMS OVERESTIMATE THE DIRECT CARBON CYCLE RESPONSE TO ANOMALOUS CLIMATE EVENTS BUT UNDERESTIMATE THE CARBON CYCLE RECOVERY TIME (I.E. LEGACY EFFECTS) AND THAT MANY TBMS PRODUCE THE RIGHT RESPONSE TO THESE EVENTS FOR THE WRONG REASONS. WE SPECIFICALLY PROPOSE TO ESTIMATE CO2 FLUXES USING GEOSTATISTICAL INVERSE MODELING. THIS APPROACH IS UNIQUE IN THAT WE CAN DIRECTLY ASSIMILATE DATASETS LIKE TEMPERATURE AND PRECIPITATION IN THE INVERSE MODEL AND THEREFORE CREATE AN EXPLICIT LINK WITH KEY CARBON CYCLE PROCESSES. WE CAN THUS DIRECTLY COMPARE ENVIRONMENTAL RELATIONSHIPS INFERRED FROM OCO-2 AND OCO-3 TO THOSE IN AN ENSEMBLE OF TBMS PROVIDING A PATHWAY TO IMPROVE PROCESS-BASED FORMULATIONS WITHIN CO2 FLUX MODELS. AS PART OF THIS EVALUATION OF ENVIRONMENTAL RELATIONSHIPS WE WILL ALSO LEVERAGE OBSERVATIONS FROM NUMEROUS NASA INSTRUMENTS INCLUDING ECOSTRESS AND SMAP TO DIAGNOSE DISCREPANCIES AMONG TBMS AND IMPROVE THEIR FUTURE DEVELOPMENT. THE PROPOSED WORK RESPONDS TO THREE SPECIFIC TASKS OUTLINED IN THE SOLICITATION: THE USE OF FLUX INVERSIONS TO ADVANCE UNDERSTANDING OF THE CARBON CYCLE INNOVATIVE ANALYSIS USING OCO-2 AND OCO-3 COMBINED WITH OTHER SATELLITE-BASED SENSORS AND STUDIES THAT USE SIF IN COMBINATION WITH LEVEL 2 CO2 OBSERVATIONS FROM OCO-2/OCO-3.