Retrieval of upper tropospheric relative humidity profiles over low clouds from the Atmospheric Infrared Sounder

In this paper we discuss a method to retrieve humidity profiles in the upper troposphere using cloud-affected radiances measured by the Atmospheric Infrared Sounder (AIRS). The magnitude of retrieval error for temperature and water vapor profiles caused by ignoring cloud presence depends strongly on the height of clouds as well as on the cloud fraction in the sensor's field of view. Error analysis based on radiative transfer calculations performed for 155 channels using a set of diverse atmospheric profiles shows that the relative humidity in the upper troposphere at pressure levels between 200 and 400 hPa could be estimated if the cloud height was lower than the height of the 800 hPa pressure level. Applying the channel ranking technique to evaluate the cloud influence in the observed spectra, we examined a high-resolution humidity map of the upper troposphere over land and sea. Citation: Ishimoto, H. (2009), Retrieval of upper tropospheric relative humidity profiles over low clouds from the Atmospheric Infrared Sounder, Geophys. Res. Lett., 36, L11814, doi:10.1029/2009GL037665.