11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Monday, 3 June 2002
An integrated algorithm for retrieving low-level stratus cloud microphysical properties using millimeter radar and microwave radiometer data
Xiquan Dong, University of Utah, Salt Lake City, UT; and G. G. Mace
Two methods have been developed for inferring the vertical profiles of cloud microphysics in liquid phase stratocumulus clouds. The first method uses cloud liquid water path derived from microwave radiometer observations and a profile of radar reflectivity together with a previously derived layer-mean cloud-droplet effective radius to infer the vertical profiles of cloud liquid water content and effective radius. This algorithm is applicable to single layer and overcast low-level stratus clouds that occur during the day. In order to extend the retrieval algorithm from a narrow to a broad range of conditions, we describe a second method that uses an empirical relationship between effective radius and radar reflectivity based on theory and the results of method 1. Very good agreement is shown between the surface-retrieved and the aircraft-observed cloud liquid water content and effective radius during the March 2000 cloud Intensive Observing Period at the Atmospheric Radiation Measurement site in Oklahoma. On average, the surface-retrieved effective radii from methods 1 and 2 differed from the corresponding aircraft data by 4% and 11%, respectively. Sensitivity studies show that the retrieved cloud-droplet effective radius from method 2 is more sensitive to the variation of radar reflectivity when the radar reflectivity is large, but not strongly dependent on the assumptions made concerning the cloud-droplet number concentration profile and shape of the size distribution.

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