Evaluation of Nimbus 7 THIR/CLE and Air Force three-dimensional Nephanalysis estimates of cloud amount

Three different estimates of the percent of fixed geographical regions (160 x 160 km) either free of cloud (clear) or covered by low, middle, and high (opaque) cloud have been intercompared. The estimates were derived by analysts interpreting geosynchronous satellite images, with concurrent meteorological observations; from Nimbus 7 temperature humidity infrared radiometer (THIR) CLOUD ERB (CLE) data; and from Air Force three dimensional nephanalysis (3DN) data. Air Force 3DN agrees better with the analyst than THIR/CLE, except for high cloud amount; the CLE and 3DN results tend to overestimate clear amount when clear amount is large and underestimate it when clear amount is small, by 10-20 percent for CLE and by 5-10 percent for 3DN, and both agree well with the analyst in the mean. Systematic and random errors for 3DN and CLE are specified. CLE estimates of cloud amount over land at night should not be used for scientific purposes unless restricted to high cloud amount. It is believed that the CLR and 3DN are the only two digitized, global cloud type and amount data sets in existence.