Remote Sensing of Cirrus Particle Size Vertical Profile Using 1.38 μm Spectrum and MODIS/ARM Data
| Wang, Xingjuan | UCLA Department of Atmospheric & Oceanic Sciences |
| Liou, Kuo-Nan | UCLA |
| Ou, Szu-cheng | University of California, Los Angeles |
| Takano, Yoshihede | UCLA Department of Atmospheric & Oceanic Sciences |
| Chen, Yong | UCLA |
Category: Cloud Properties
The time series of backscattering coefficients derived from lidar and Doppler millimeter-wave radar returns, as well as from balloon and aircraft in-situ measurements have shown that cirrus clouds exhibit significant vertical inhomogeneity in terms of ice crystal sizes and shapes. The vertical variation of ice crystal size can alter the radiative heating/cooling profiles in cirrus cloudy atmospheres and hence is an important component in the study of cloud-radiation and climate feedback. We have simulated the 1.38 μm (6600-7500 cm−1) bidirectional reflectance spectra in cirrus cloudy conditions on the basis of an adding-doubling radiative transfer program coupled with the correlated k distribution approach for sorting absorption lines using a 0.01cm−1 spectral interval. Based on the sensitivity of 1.38 μm spectral reflectance on water vapor absorption, a conceptual approach has been developed to infer the vertical distribution of ice crystal mean effective size. We have selected 17 channels, 12 of them are located between 6600 and 6800 cm−1 where the ice crystal single-scattering albedo is sensitive to cloud particle size. The remaining 5 channels are located between 7200 and 7500 cm−1 where the cirrus cloud absorption is minimal and reflectance is dependent on cloud optical depth. Channels with the relatively strong water vapor absorption in this region also bear information on cloud temperature. A library of reflectance at the 17 channels for a variety of two-layer cirrus clouds has been built and a three-step retrieval scheme based on the look-up table approach has been developed. Synthetic retrievals using a minimization method that were conducted for a number of cases involving small ice crystals aloft and large particles below have illustrated some success. Finally, we apply the principle of the multiple-layer multi-channel retrieval scheme to the MODIS (0.645, 1.375, 1.64, 2.13, and 3.75 μm) data over the ARM site and carry out preliminary validation of the retrieval results using independent ground-based lidar/radar measurements.
This poster will be displayed at the ARM Science Team Meeting.
