The stratospheric changes inferred from 10 years of AIRS and AMSU-A radiances

Abstract

e analyze global-mean radiances observed by AIRS (Atmospheric Infrared Sounder) and AMSU-A (Advanced Microwave Sounding Unit) from 2003 to 2012. We focus on channels sensitive to emission and absorption in the stratosphere. Optimal fingerprinting is used to obtain estimates of changes of stratospheric temperature in five vertical layers due to external forcing in the presence of natural variability. Natural variability is estimated using synthetic radiances based on the 500-year GFDL CM3 and 240-year HADGEM2-CC control runs. The results show a cooling rate of 0.65±0.11(2σ) K decade-1 in the upper stratosphere above 6hPa, ~0.46±0.24 K decade-1 in two middle stratospheric layers between 6hPa and 30hPa, and 0.39±0.32 K decade-1 in the lower stratosphere (30-60hPa). The cooling rate in the lowest part of the stratosphere (60-100hPa) is -0.014±0.22 K decade-1, which is smallest among all five layers and statistically insignificant. The synergistic use of well-calibrated passive infrared and microwave radiances permits disambiguation of trends of carbon dioxide and stratospheric temperature, increases vertical resolution of detected stratospheric temperature trends, and effectively reduces uncertainties of estimated temperature trends.