Validation of AIRS/AMSU-A water vapor and temperature data with in situ aircraft observations from the surface to UT/LS from 87°N-67°S

Validation of the Atmospheric Infrared Sounder (AIRS)/Advanced Microwave Sounding Unit (AMSU-A) data set with in situ observations provides useful information on its application to climate and weather studies. However, different space/time averaging windows have been used in past studies, and questions remain on the variation of errors in space, such as between land/ocean and the Northern/Southern Hemispheres. In this study, in situ aircraft measurements of water vapor and temperature are compared with the AIRS/AMSU-A retrievals (Version 5 Level 2) from 87 degrees N to 67 degrees S and from the surface to the upper troposphere and lower stratosphere (UT/LS). By using a smaller comparison window (1h and 22.5km) than previous studies, we show that the absolute percentage difference of water vapor (|dH(2)Operc|) is similar to 20-60% and the absolute temperature difference (|dTemp|) is similar to 1.0-2.5K. The land retrievals show improvements versus Version 4 by similar to 5% in water vapor concentration and similar to 0.2K in temperature at 200-800 mbar. The land (ocean) retrievals are colder and drier (warmer and moister) than the in situ observations in the boundary layer, warmer and drier (warmer and moister) at the UT/LS. No significant differences between hemispheres are noted. Overall, future comparisons are suggested to be done within 4h and 100km in order to keep the errors from window sizes within similar to 10%. To constrain the uncertainties in previous validation results, we show that every 22.5km (or 1h) increment in window sizes contributes to similar to 2% |dH(2)Operc| and similar to 0.1K |dTemp| increases.