Climatic Atlas of Clouds Over Land and Ocean

This data set contains revised and updated versions of the maps presented twenty years ago in atlases of cloud climatological data obtained from visual observations at the Earth’s surface. The cloud averages presented on these maps come from digital archive of gridded land and ocean cloud climatological data and supersede the first cloud climatology. The new land maps based on analyses of 185 million visual cloud observations made at 5,388 weather stations on continents and islands over 26 years (1971-1996) rather than 11. The ocean maps are based on analyses of 50 million cloud observations made from ships over a 44-year period (1954-1997) rather than 30 years. Precipitation maps for both land and ocean are based on 1982-91 data. Also, more cloud types are distinguished in the low and middle levels, and the analysis procedures have been improved, particularly as regards the nighttime observations. Earlier climatic summaries were previously produced as Carbon Dioxide Information Analysis Center (CDIAC) Numeric Data Packages NDP-026C and NDP-026D. Two grid sizes are used to display the new cloud averages. Most data are given at 5-degree latitude-longitude resolution (with coarser longitudinal resolution toward the poles to preserve approximately equal-area grid boxes). A 10-degree grid (also with coarser longitudinal resolution toward the poles) is used for some ocean data. For each grid box, the digital database includes multi-year annual, seasonal and monthly averages, and the amplitude and phase of annual and diurnal cycles. Averages are given for total cloud cover, clear-sky frequency, and nine cloud types [five in the low level: fog, stratus, stratocumulus, cumulus, and cumulonimbus; three in the middle level: nimbostratus, altostratus, and altocumulus; and one in the high level: all cirriform clouds combined]. Cloud amounts and frequencies-of-occurrence are given for all types, and average base heights are given for the low cloud types.