Recent Changes in Cloud Cover and Cloud Types over the Arctic

Recent rapid changes in sea ice extent and thickness may partially be affected by cloud radiative forcing, and sea-ice changes could in turn impart changes in cloud cover. We are analyzing visual cloud reports, which are made on land by weather stations, and in the Arctic Ocean by ships and drifting ice stations. Total cloud amount is reported, as well as the amounts of the different cloud types: the low clouds cumulus, cumulonimbus, stratus, stratocumulus, and fog; the middle clouds nimbostratus, altostratus and altocumulus; and the high (cirrus-type) clouds. Data are available over land beginning 1971, and over ocean beginning 1954, with no change in observing procedures.

An arctic cloud climatology has been produced for total cloud cover and the nine cloud types. The cloud climatology suggests a division of the arctic into two distinct regions, 'High' and 'Low' Arctic, based on seasonal cycles of stratiform cloudiness.

Interannual variations of cloud amounts show significant trends and correlations with other climatic variables, such as surface air temperature, total sea ice extent, and the Arctic Oscillation. Composite climatologies are formed for the five years of maximum September ice extent and the five years of minimum ice extent. Reduced September ice extent tends to be preceded by more extensive stratocumulus and cirrus in winter and spring. Following an anomalously low September ice extent the autumn has more stratus and altocumulus, but the winter tends to be less cloudy. The trends obtained show some disagreements with those obtained from satellite data. We also compare the observed trends to the cloud changes predicted by GCM's with climatic warming.