MICROPHYSICAL AND RADIATIVE PROPERTIES OF BOUNDARY-LAYER STRATIFORM CLOUDS DEDUCED FROM GROUND-BASED MEASUREMENTS

Two methods for retrieving the microphysical and radiative properties of marine and continental boundary layer stratiform clouds from ground -based measurements are implemented. The first method uses measurement s of the cloud liquid water path and the cloud nadir radiance at 1 mu m to infer the cloud optical depth, cloud droplet effective radius, an d cloud droplet concentration. In the second method a delta 2-stream r adiative transfer model is used to retrieve the microphysical and radi ative properties of stratiform clouds from measurements of the cloud l iquid water path, the cloud geometric thickness, the downward shortwav e irradiance at the surface, and atmospheric profiles of temperature, pressure, and relative humidity. In all of the retrievals the cloud dr oplets are assumed to have a lognormal size distribution with a logari thmic width of 0.35; the cloud droplet modal radius and cloud droplet concentration are free parameters. Data obtained in the Azores and Okl ahoma from marine and continental boundary layer stratiform clouds, re spectively, are used in the study.-Results of the analysis demonstrate d that the retrieved cloud droplet effective radii from the marine clo uds (13 mu m) were generally larger than the values from continental c louds (7 mu m), while cloud droplet number concentrations were much le ss in marine clouds (150 cm(-3)) than in continental clouds (500 cm(-3 )). The retrieved cloud droplet effective radius had a strong negative correlation with the cloud droplet concentration. The effects of unce rtainties in the measurements, the cloud droplet distribution width, a nd the Surface albedo on the retrieved properties were evaluated by us ing the delta 2-stream model. The errors in the retrieved cloud radiat ive properties were generally less than 5%, while the errors in the re trieved cloud microphysical properties were considerably larger.