Assimilation of thermodynamic information from advanced infrared sounders under partially cloudy skies for regional NWP

Generally, only clear‐infrared spectral radiances (not affected by clouds) are assimilated in weather analysis systems. This is due to difficulties in modeling cloudy radiances as well as in observing their vertical structure from space. To take full advantage of the thermodynamic information in advanced infrared (IR) sounder observations requires assimilating radiances from cloud‐contaminated regions. An optimal imager/sounder cloud‐clearing technique has been developed by the Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin‐Madison. This technique can be used to retrieve clear column radiances through combining collocated multiband imager IR clear radiances and the sounder cloudy radiances; no background information is needed in this method. The imager/sounder cloud‐clearing technique is similar to that of the microwave/IR cloud clearing in the derivation of the clear‐sky equivalent radiances. However, it retains the original IR sounder resolution, which is critical for regional numerical weather prediction applications. In this study, we have investigated the assimilation of cloud‐cleared IR sounder radiances using Atmospheric Infrared Sounder (AIRS)/Moderate Resolution Imaging Spectroradiometer for three hurricanes, Sandy (2012), Irene (2011), and Ike (2008). Results show that assimilating additional cloud‐cleared AIRS radiances reduces the 48 and 72 h temperature forecast root‐mean‐square error by 0.1–0.3 K between 300 and 850 hPa. Substantial improvement in reducing track forecasts errors in the range of 10 km to 50 km was achieved. Key Points The application of IR cloud clearing for radiance assimilation in NWP The benefits of assimilating AIRS/MODIS cloud‐cleared radiances are discussed Forecasts are substantially improved with assimilating cloud‐cleared radiances