A Climatology of Midlatitude Continental Clouds from the ARM SGP Central Facility:Part III: Comparison of low cloud properties between GOES and surface
| Dong, Xiquan | University of North Dakota |
Dong, X.(a), Minnis , P.(b), Xi, B.(a), and Khaiyer, M. (c) University of North Dakota (a) NASA Langley Research Center (b) AS&M Inc (c) Point of contact: Xiquan Dong, dong@aero.und.edu; phone: 701-777-6991 A statistical comparison has been performed from 6-yr of single-layer and overcast low-level stratus cloud macrophysical and microphysical properties derived from both surface and GOES observations at the Atmospheric Radiation Measurement (ARM) Southern Great Plains Central Facility (SCF). The dataset includes approximately 1206 hours of daytime and 765 hours of nighttime results during the 6-yr period from January 1997 to December 2002. For the surface results, the cloud-base and -top heights and temperatures are derived from a ground-based radar and lidar pair, and rawinsonde sounding; cloud liquid water path (LWP) is retrieved from ground-based microwave radiometer measured brightness temperature; and cloud-droplet effective radius (re), cloud optical depth (), top-of-atmosphere albedo (RTOA) are calculated from a new parameterization. All surface results are averaged to half-hour temporal resolution to match the GOES results. The GOES results, retrieved from VISST for daytime (SZA<82o) and from SIST for nighttime (SZA>87.5o), are averaged in a 25-km radius centered on the ARM SGP site. The VISST relies on the infrared (IR, 10.8 µm) radiance to determine effective cloud temperature (as well as height with ECMWF sounding), the visible reflectance to obtain cloud optical depth, the solar-infrared (SI; 3.9 µm) radiance to estimate cloud particle size, and the split-window channel (SWC, 12.0 µm) to help determine phase. The SIST utilizes the SIR, IR, and SWC channels simultaneously to determine cloud macrophysical properties. In spite of the large differences in temporal and spatial resolution between surface and GOES, the GOES results agree reasonably well with the surface data from a statistical point of view. The cloud properties were analyzed in terms of their seasonal, monthly, and hourly variations. In general, more stratus clouds occur during winter and spring than in summer and fall seasons. Cloud-layer altitudes were higher in summer than in winter, the highest in middle afternoon (~1600-1700 LT) and the lowest in middle morning (~1000-1100 LT). The daytime GOES-derived effective cloud temperature (Te =278.3 K) and height (Ze =1.664 km) are very close to the surface-derived cloud-top temperature (Ttop =277.8 K) and height (Ztop =1.849 km), and the nighttime comparisons are similar to their daytime counterparts. The correlations between Ze (Te) and mean cloud height (temperature) are 0.36 (0.79) for daytime, and 0.45 (0.83) for nighttime. The annual averages of the daytime surface-derived re, LWP, and RTOA are 9.1 m, 123.7 gm-2, 21.1, and 0.517; their GOES counterparts are 10.8 m, 147.8 gm-2, 19.6, and 0.466; and their corresponding correlations are 0.12, 0.65, 0.65, and 0.73, respectively.
This poster will be displayed at the ARM Science Team Meeting.