P2.19
The study of cirrus clouds using ground-based high spectral resolution infrared measurements
Guang Guo, Texas A&M University, College Station, TX; and Q. Ji, P. Yang, and S. C. Tsay
The radiation budget, climate change and feedback processes involving clouds are important. In the tropics, the radiative heating/cooling and forcing are strongly modulated by cirrus clouds due to the fact that these clouds occur frequently and ubiquitously. Here we report an algorithm for inferring the microphysical and radiative properties of cirrus clouds ( i.e., effective size, ice water path, optical thickness and cloud emissivity) from ground-based high-spectral-resolution infrared observations. This approach is based on the fact that the downward radiance is sensitive to the cloud optical thickness in the 800~1200 cm-1 atmospheric window region. Additionally, the spectral slope of the brightness temperature for the downward radiance is sensitive to both the effective radius of ice crystals and the optical thickness of cirrus clouds. This spectral feature of atmospheric infrared radiation allows us to retrieve three microphysical properties of cirrus clouds simultaneously. In practice, we employ a “curve enveloping” technique to avoid the effect of a “non-absorption band shift”. Thirty in-situ size distributions are used to calculate the mean scattering properties of ice crystals in cirrus clouds. The clear sky optical thickness and downward radiance are simulated by a line-by-line radiative transfer model and the discrete-ordinate-method radiative transfer model, respectively. Furthermore, we use sky images and normalized lidar backscatter profiles to identify cloudy and cloud-free conditions. As a case study, we apply the present algorithm to the retrieval of cirrus properties on the basis of the surface infrared spectrum acquired during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) in July 2002.
Poster Session 2, Atmospheric, Oceanic and Land Observations
Wednesday, 14 January 2004, 2:30 PM-4:00 PM, Hall AB
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