A survey of changes in cloud cover and cloud types over land from surface observations 1971–96

• Main Authors: Stephen G. Warren, Ryan, M. Eastman, Carole J. Hahn
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: Arctic; Many Islands
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.469.3901; http://www.atmos.washington.edu/~ignatius/CloudMap/Publications/WarrenEtal2007_CloudSurvey.pdf

From a dataset of weather observations from land stations worldwide, about 5400 stations were selected as having long periods of record with cloud-type information; they cover all continents and many islands. About 185 million synoptic reports were analyzed for total cloud cover and the amounts of nine different cloud types, for the 26-yr period 1971–96. Monthly and seasonal averages were formed for day and night separately. Time series of total-cloud-cover anomalies for individual continents show a large decrease for South America, small decreases for Eurasia and Africa, and no trend for North America. The largest interannual variations (2.7%) are found for Australia, which is strongly influenced by ENSO. The zonal average trends of total cloud cover are positive in the Arctic winter and spring, 60°–80°N, but negative in all seasons at most other latitudes. The global average trend of total cloud cover over land is small,0.7 % decade1, offsetting the small positive trend that had been found for the ocean, and resulting in no significant trend for the land–ocean average. Significant regional trends are found for many cloud types. The night trends agree with day trends for total cloud cover and for all cloud types except cumulus. Cirrus trends are generally negative over all