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A Gridded Climatology of Clouds over Land (1971-1996) and Ocean (1954-2008) from Surface Observations Worldwide (NDP-026E)*

PDF PDF File   data Data (NDP-026E)

Date of Publication

Original date of publication: December 2007.

*Updated August, 2010:
This page and the global cloudiness dataset and documentation were updated to reflect an additional 11 years (through 2008) of ocean data added by the investigators in December, 2009. Also, two new data directories (cat_55-70 and cat_71-82) were added containing the updated data and additional ancillary files were added to the directory: ancillary_ocean_files. Please see the new APPENDIX U in ndp026e.pdf containing information on this update.

The recommended citation reflecting the updating of this database is:

Hahn, C.J., and S.G. Warren, 2007 (updated 2009): A Gridded Climatology of Clouds over Land (1971-1996) and Ocean (1954-2008) from Surface Observations Worldwide. Numeric Data Package NDP-026E, CDIAC, Department of Energy, Oak Ridge, Tennessee. (Documentation, 71 pages; plus a 4-page appendix describing an update of ocean cloud averages for the years 1998-2008.)


C. J. Hahn,
Dept. of Atmospheric Sciences,
University of Arizona

S. G. Warren,
Dept. of Atmospheric Sciences,
University of Washington



Map of Worldwide Total Cloud Cover


Surface synoptic weather reports from ships and land stations worldwide were processed to produce a global cloud climatology which includes: total cloud cover, the amount and frequency of occurrence of nine cloud types within three levels of the troposphere, the frequency of occurrence of clear sky and of precipitation, the base heights of low clouds, and the non-overlapped amounts of middle and high clouds. Synoptic weather reports are made every three hours; the cloud information in a report is obtained visually by human observers. The reports used here cover the period 1971-96 for land and 1954-2008 for ocean.

This digital archive provides multi-year monthly, seasonal, and annual averages in 5x5-degree grid boxes (or 10x10-degree boxes for some quantities over the ocean). Daytime and nighttime averages, as well as the diurnal average (average of day and night), are given. Nighttime averages were computed using only those reports that met an "illuminance criterion" (i.e., made under adequate moonlight or twilight), thus minimizing the "night-detection bias" and making possible the determination of diurnal cycles and nighttime trends for cloud types. The phase and amplitude of the first harmonic of both the diurnal cycle and the annual cycle are given for the various cloud types. Cloud averages for individual years are also given for the ocean for each of 4 seasons, and for each of the 12 months (daytime-only averages for the months). [Individual years for land are not gridded, but are given for individual stations in a companion data set, CDIAC's NDP-026D).]

This analysis used 185 million reports from 5388 weather stations on continents and islands, and 50 million reports from ships; these reports passed a series of quality-control checks. This analysis updates (and in most ways supercedes) the previous cloud climatology constructed by the authors in the 1980s. Many of the long-term averages described here are mapped on the University of Washington, Department of Atmospheric Sciences Web site.

The Online Cloud Atlas containing NDP-026E data is available via the University of Washington.

Last updated 8/2010