Journal of Geophysical Research: Atmospheres
AIRS, AMSU, water vapor, relative humidity, validation
Climate | Meteorology
 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°N to 67°S and from the surface to the upper troposphere and lower stratosphere (UT/LS). By using a smaller comparison window (1 h and 22.5 km) than previous studies, we show that the absolute percentage difference of water vapor (|dH2Operc|) is ~20–60% and the absolute temperature difference (|dTemp|) is ~1.0–2.5 K. The land retrievals show improvements versus Version 4 by ~5% in water vapor concentration and ~0.2 K 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 4 h and 100 km in order to keep the errors from window sizes within ~10%. To constrain the uncertainties in previous validation results, we show that every 22.5 km (or 1 h) increment in window sizes contributes to ~2% |dH2Operc| and ~0.1 K |dTemp| increases.
Minghui Diao, Loayeh Jumbam, Justin Sheffield, Eric Wood, and Mark Zondlo. "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" Journal of Geophysical Research: Atmospheres (2013). https://doi.org/10.1002/jgrd.50483