Relationship between clouds, temperature and humidity in NOAA IASI retrievals

The NOAA Infrared Atmospheric Sounding Interferometer (IASI) retrieval system has been operated at STAR/NESDIS since 2008. Its retrieval approach includes procedures of radiance calibration, microwave retrieval, cloud clearing, initial IR retrieval, and a final iterative physical retrieval. The L2 retrievals are based on the cloud-clearing method that combines the infrared radiances of IASI at 2 x 2 footprints and microwave radiance at the co-registrated single AMSU footprint. The L2 support product of temperature and moisture profiles has a horizontal resolution of ~ 45 km at nadir and is reported at 100 vertical levels. Associated cloud properties (including effective cloud fraction, cloud-top temperature and pressure) are reported at the 2x2 footprint resolution for up to 2 cloud layers.

The study uses three years (2009-2012) of IASI retrievals spatially and temporally collocated to global radiosonde data, collected at the NOAA Products Validation system (NPROVS, http://www.star.nesdis.noaa.gov/smcd/opdb/poes/NPROVS.php) to investigate the relationship between clouds, temperature, and humidity within the IASI retrieval system. Specially, we want to understand (a) if the retrieved cloud properties are thermo-dynamically consistent to temperature and humidity retrievals, and (b) what are the impacts of cloud presence and cloud clearing on the accuracies of the retrievals. This analysis is conducted in a statistical way for different atmospheric and surface conditions and for different cloud fraction classes. Radiosonde measurements are used as the reference to define the retrieval accuracy and comparison of the final physical retrievals with their first guess is used to infer the impact of the cloud clearing procedure. We discuss how such analysis can advance our understanding of the internal consistency of major components within the retrieval system and, furthermore, if major geophysical variables derived from the hyper spectral sounder represent a nominal level of maturity for application in climate monitoring. Methodologies developed from the study may be useful for evaluating the Environmental Data Records (EDRs) developed from the Cross-track Infrared and Microwave Sounder Suite (CrIMSS) on board Suomi NPP launched in 2011.