Modeling and analysis of MLS 203 and 186.5GHz radiances at 14-18km tangent heights

This paper presents a radiative transfer modeling study of cloud-induced limb radiances at 14-18km tangent heights and its application to UARS MLS data. In the presence of thick-and-dense clouds, MLS observations show that the radiances near ~200GHz are significantly enhanced by cloud ice scattering and emission. Using a two-frequency technique (203 and 186.5GHz), one can separate contributions between cloud and water vapor, allowing retrieval of cloud properties. By incorporating a realistic ice particle size parameterization [McFarquhar and Heymsfield, JAS, 1997], we are able to model and interpret MLS cloud signals at 14-18km tangent heights more accurately. Preliminary calculations suggest that these signals are likely due to the scattering of large ice particles brought up to these altitudes by strong deep convection. The calculated brightness temperatures from cloud scattering are in line with MLS observations, showing a variation of 0-60K at 16km for ice water content of 0-0.1 g/m3. In the light of this study, the 203 and 186.5GHz limb sounding could provide a good remote sensing technique to measure ice content at the top of heavy convective clouds such as cumulonimbus.