Collaborative Research: Testing Climate Models by Feedback Analysis Using Atmospheric Infrared Sounder (AIRS) and Global Positioning System (GPS) Radio Occultation Data

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Outgoing longwave spectra obtained by the Atmospheric Infrared Sounder (AIRS) and GPS radio occultation data obtained by the CHAMP (Challenging Mini-satellite Payload) and COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) missions will be analyzed to provide observational constraints on longwave feedbacks and radiative forcing in the climate system. The high-spectral-resolution radiance measurements of AIRS contain the fingerprints of radiative forcing by a variety of atmospheric thermodynamic variables and constituent concentrations, and these fingerprints lead directly to longwave greenhouse forcing and atmospheric feedbacks. Because clouds and surface temperature contribute similar spectral signatures, radio occultation will provide the information to distinguish between the two. The investigators found, under their previous NSF support, that radio occultation trends constrain the surface air temperature response of climate models while infrared spectral radiance trends unambiguously constrain radiative forcing of the climate and the longwave feedbacks in climate models. Now they will apply these findings to the aforementioned satellite data to obtain estimates of radiative forcing by well-mixed greenhouse gases globally to at least 10% uncertainty, to estimate tropical water vapor and cloud longwave feedbacks to ~7% uncertainty by anomaly analysis, and to begin the estimation of global longwave feedbacks by trend analysis, albeit with large uncertainties due to natural variability.Broader impacts of this work lie in its use of optimal fingerprinting using multiple data types to test climate models against satellite data, and in the field of climate prediction. Highly accurate and reliable data will be used to provide strong observational constraints on climate models. The ultimate goal of this research program is to improve our skill at decadal scale climate projection. In addition, graduated students from the joint Harvard and University of Michigan efforts will be supported.