Evaluation of AIRS V5 temperature profiles using matched retrievals from COSMIC and ECMWF analyses

An evaluation of the Atmospheric Infrared Sounder (AIRS) version 5 temperatures is performed using retrievals from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) and analyses from the European Center for Medium-Range Weather Forecasts (ECMWF). Utilizing averaging kernels from AIRS, collocated temperatures were compared under different cloud conditions and surface types. The profiles over a 33 month period (July 2006 through March 2009) were sampled onto a regular grid at 100 AIRS pressure levels with a temporal resolution of 5 days and latitudinal resolution of 10 degrees. Results reveal that the AIRS temperatures are in generally good agreement with those from COSMIC. Time-mean temperature differences are of the order 0.5 K and the root mean square (RMS) deviations are of the order 1 K. Clouds occurring over oceans affect the mean temperature differences by as much as 0.3 K. Their effect over land is more pronounced, leading to differences as large as 0.5K. The significant differences in zonal profiles of AIRS RMS values when compared to those from ECMWF analyses are explained in terms of an annual variation in the AIRS temperatures relative to those from COSMIC and ECMWF. In the Southern hemisphere, this variation occurs at all latitudes South of 60S and maximizes at 50mb. The variation in the Northern hemisphere is less pronounced and is confined to polar latitudes near 50mb.