The Nimbus-7 Global Cloud Climatology

Abstract

A total of six years (April 1979 to March 1985) of continuous measurements from the Temperature Humidity Infrared Radiometer (THIR) and the Total Ozone Mapping Spectrometer (TOMS), both on the Nimbus-7 satellite, have been processed to form the Nimbus-7 Global Cloud Climatology (N7GCC). The cloud-estimation algorithms utilize THIR ?11.5-micron? radiances, TOMS-derived ?0.37-micron? reflectivities, climatological temperature lapse rates and concurrent surface temperatures, and snow-ice information. (The last two items are taken from the Air Force three-dimensional nephanalysis archive.) This cloud climatology gives, near local noon and midnight, the fractional area covered by high-level clouds middle-level clouds and low-altitude clouds, and the total fractional area covered by all clouds (total cloud). Statistics are also given for the special cloud types: cirrus, deep convective, and warm low-altitude clouds. lie cloud and clear-sky radiances, together with correlative surface temperatures, are included. These products have the same spatial resolution and temporal (daily and monthly) resolution as the independently derived concurrent Nimbus-7 Earth Radiation Budget data set. The N7GCC has been compared with preliminary results from the International Satellite Cloud Climatology Project (ISCCP) and with other cloud data sets. For July 1983, the mean global cover was estimated to be 49 percent by N7GCC and 63 percent by ISCCP. Older cloud climatologies showed average July global cloud cover in the 50 percent to 60 percent range.