A Climatology of Midlatitude Low Clouds from the ARM SGP Site: Part II: Comparison between GOES and ARM Surface Observations
Dong, X.(a), Minnis, P.(b), Rollefson, S.(a), Khaiyer, M.M.(c), and Xi, B.(a), University of North Dakota (a), NASA Langley Research Center (b), AS&M Inc (c)
Fourteenth Atmospheric Radiation Measurement (ARM) Science Team Meeting
In Part II of this series of papers examining the climatological properties of the low clouds studied over the ARM SGP site, we compare low cloud macrophysical, microphysical, and optical properties derived from surface and GOES data from January 2000 to December 2001. The cloud macrophysical properties include cloud height and temperature, and cloud microphysical/optical properties contain cloud-droplet effective radius, optical depth, LWP, and TOA albedo. For the surface data, the cloud-base height is derived laser ceilometer and cloud top height is derived cloud radar, and cloud temperatures are measured from ARM radiosonde sounding. For the surface retrievals, the cloud-droplet effective radius and optical depth are retrieved from a delta2-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. All surface data are averaged to half-hour temporal resolution to match the GOES results. 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 GOES radiances were calibrated by Minnis et al. (2002) using collocated measurements from the Tropical Rainfall Measuring Mission Visible Infrared Scanner (VIRS). Cloud temperature Tc, visible (VIS, 0.65 µm) optical depth, re, and LWP were derived by Minnis et al. (2001) from the multispectral GOES imager data using the visible infrared solar-infrared split-window technique (VISST), an updated version of the three channel technique described by Minnis et al. (1995). VISST relies on the infrared (IR, 10.8 µm) radiance to determine cloud temperature, 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 (Young et al. 1997). These parameters are determined iteratively for each pixel by matching the observations with a set of theoretical calculations with estimated instantaneous uncertainties of 15% for re and 12% for tau.
Note: This is the poster abstract presented at the meeting; an extended version was not provided by the author(s).
