VALIDATION OF SATELLITE RETRIEVALS OF CLOUD MICROPHYSICS AND LIQUID WATER PATH USING OBSERVATIONS FROM FIRE

Cloud effective radii (r(e)) and cloud liquid water path (LWP) are der ived from ISCCP spatially sampled satellite data and validated with gr ound-based pyranometer and microwave radiometer measurements taken on San Nicolas Island during the 1987 FIRE IFO. Values of r(e) derived fr om the ISCCP data are also compared to values retrieved by a hybrid me thod that uses the combination of LWP derived from microwave measureme nt and optical thickness derived from GOES data. The results show that there is significant variability in cloud properties over a 100 km x 80 km area and that the values at San Nicolas Island are not necessari ly representative of the surrounding cloud field. On the other hand, e ven though there were large spatial variations in optical depth, the r (e) values remained relatively constant (with sigma less than or equal to 2-3 mu m in most cases) in the marine stratocumulus. Furthermore, values of r(e) derived from the upper portion of the cloud generally a re representative of the entire stratiform cloud. When LWP values are less than 100 g m(-2), then LWP values derived from ISCCP data agree w ell with those values estimated from ground-based microwave measuremen ts. In most cases LWP differences were less than 20 g m(-2). However, when LWP values become large (e.g., greater than or equal to 200 g m(- 2)), then relative differences may be as large as 50%-100%. There are two reasons for this discrepancy in the large LWP clouds: 1) larger ve rtical inhomogeneities in precipitating clouds and 2) sampling errors on days of high spatial variability of cloud optical thicknesses. Vari ations of r(e) in stratiform clouds may indicate drizzle: clouds with droplet sizes larger than 15 mu m appear to be associated with drizzli ng, while those less than 10 mu m are indicative of nonprecipitating c louds. Differences in r(e) values between the GOES and ISCCP datasets are found to be 0.16 +/- 0.98 mu m.