Digital Databases:

Extended Edited Cloud Reports from Ships and Land Stations over the Globe, 1952-1996.   http://cdiac.ornl.gov/epubs/ndp/ndp026c/ndp026c.html

Cloud Climatology for Land Stations Worldwide, 1971-1996.   http://cdiac.ornl.gov/epubs/ndp/ndp026d/ndp026d.html

Gridded Climatology of Clouds over Land (1971-96) and Ocean (1954-2008) from Surface Observations Worldwide.  http://cdiac.ornl.gov/epub/sndp/ndp026e/ndp026e.html