Using ARM data to correct plane-parallel satellite retrievals of cloud properties
| Dong, Xiquan | University of North Dakota |
| Minnis, Patrick | NASA Langley Research Center |
| Xi, Baike | University of North Dakota |
| Khaiyer, Mandana | Analytical Services and Material, Inc. |
Category: Cloud Properties
The angular variations of cloud properties derived from GOES data are examined using simultaneously collocated ARM surface observations/retrievals at the DOE ARM SGP site during the 6-yr period from January 1997 to December 2002. The dependencies of GOES cloud retrievals on solar zenith angle (SZA), scattering angle (SCA), and relative azimuth angle (RZA) are investigated for single-layer and overcast low-level stratus clouds. The GOES-retrieved cloud-droplet effective radius (re), optical depth (τ), LWP and TOA albedo (Rtoa) increase significantly with increasing SZA. For example, when SZA increases from 16o to 81o, re increases from 9.7 to 12.6 µm (13.4%), τ from 10.3 to 31.3 (194%), LWP from 71 to 270 (280%), and Rtoa from 0.36 to 0.66 (83%). At the same time, the surface-observed cloud properties are nearly independent of SZA except that Rtoa increases with increasing SZA. For the SCA dependence, the GOES-derived re is much larger than surface retrievals before reaching a minimum at 125o, then climbs up to 175o; τ trends in the opposite direction to re for SCA<125o, then fluctuates at smaller values. Consequently, LWP has a small variation with SCA, a composite result of both re and τ. The GOES-derived cloud properties vary with RZA in manner similar to those for SCA, but are not observed at angles < 90o. Techniques are developed for empirically correcting for the angular dependence of the GOES-derived cloud properties.
This poster will be displayed at the ARM Science Team Meeting.
