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

Monday, 3 June 2002
Comparison of Stratus Cloud Properties Deduced from Surface, GOES, and Aircraft Data during the March 2000 ARM Cloud IOP
Xiquan Dong, Univ. of Utah, Salt Lake City, UT; and P. Minnis, G. G. Mace, W. L. Smith Jr., M. Poellot, R. T. Marchand, and A. D. Rapp
Low-level stratus cloud microphysical properties derived from surface and GOES data during the March 2000 cloud IOP at the ARM SGP site are compared with aircraft in situ measurements. For the surface retrievals, the cloud-droplet effective radius and optical depth are retrieved from a 2-stream radiative transfer model with the input of ground-based measurements, and cloud liquid water path (LWP) is retrieved from ground-based microwave radiometer measured brightness temperature. The satellite results, retrieved from GOES visible, solar-infrared, and infrared radiances, are averaged in a 0.5 x 0.5 box centered on the ARM SGP site. The FSSP on the University of North Dakota Citation aircraft provided in situ measurements of the cloud microphysical properties. During the IOP, four low-level stratus cases were intensively observed by the ground- and satellite-based remote sensors and aircraft in situ instruments resulting in a total of 10 hours of simultaneous data from the three platforms. In spite of the large differences in temporal and spatial resolution between surface, GOES, and aircraft, the surface retrievals have excellent agreement with the aircraft data overall for the entire 10-hour period, and the GOES results agree reasonably well with the surface and aircraft data and have similar trends and magnitudes. Most of the GOES-derived effective radii are larger than the surface and aircraft results, and their mean for the 10-hour period is about 2 mm larger than the surface and aircraft means. There is excellent agreement in cloud LWP and optical depth and almost the same mean values from three datasets for the 10-hour period with high correlation coefficients (~0.8) between the three datasets. On average, the aircraft deduced cloud-droplet effective radius, LWP and optical depth differed from the corresponding surface retrievals by 4%, 1% and 8%, respectively, while they differed from those derived from GOES by 23%, 2%, and 5%, respectively during the 10-hour period. Additional surface-satellite datasets were analyzed for time periods when the aircraft was unavailable. When these additional results are combined with the retrievals from the four in situ cases, the mean satellite-derived values of cloud-droplet effective radius, LWP and optical depth differ from their surface-based counterparts by 16%, 4%, and 6%, respectively. The frequency distributions of the two datasets are very similar indicating that the satellite retrieval method should be able to produce reliable statistics of boundary-layer cloud properties for use in climate and cloud process models.

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