Validation of a Direct Cooling Rate Retrieval Method Using AIRS and TES Data

An accurate and computationally-efficient means for deriving heating and cooling rate profiles at small horizontal resolution in the Tropical Tropopause Layer is necessary for the understanding of stratospheric water vapor transport. We first present a formal error budget analysis for clear-sky infrared radiative cooling rates in that region with respect to uncertainties in atmospheric temperature, water vapor, and other pertinent profiles. Subsequently, we explore the extent to which current hyperspectral thermal infrared sounders such as AIRS and TES describe the clear-sky infrared cooling rate profiles within a retrieval-based optimal estimation framework. Next, we detail formal and ad hoc methods for treating the absence of spectral coverage for wavelengths longer than 15.4 μm and tabulate a computational cost budget comparing our methods with standard ones for calculating cooling rate profiles. Our approach to directly infer cooling rate profile from space is cross-validated using in situ water vapor, temperature, and ozone profile data from the Fall 2004 Aura Validation Experiment. Finally, we show that data from the advanced, though under-utilized, extended staring capability of the TES instrument is well-suited for application to the understanding of cooling rate profiles.