Possible causes of recent changes in the Arctic cloud cover, surface temperature, and temperature inversions.

摘要

Arctic surface temperature, total cloud, heat and moisture convergence, and sea ice concentration are changing in ways that are a function of season and geographic regions. For surface temperature, a significant cooling trend over the Arctic Ocean in winter, and a significant warming trend in the Arctic in spring and summer from 1982 to 2000 are found. Consistent with the surface temperature trend, trends in total cloud cover show a significant negative trend over the Arctic Ocean in winter, and generally a positive trend in the Arctic in spring and summer. These trends cannot be explained completely by changes in the Arctic Oscillation.; Changes in cloud cover influence surface temperature changes observed from satellites. The all-sky surface temperature trend can be partitioned into two parts: the first part is related to the combination of the surface temperature trends under clear-sky and cloudy conditions; the second part is caused by the cloud cover change and the surface temperature difference between cloudy and clear-sky conditions. The relative importance of these two parts differs seasonally, with the second part more important in winter, and the first part more important in spring, summer and autumn.; The mechanisms behind the total cloud cover changes vary with region and season. Moisture convergence in winter from 1982 to 1998 shows a significant negative trend over the Nansen Basin and parts of the Barents and Kara Seas (75--90°N, 45--90°E). Over this region, correlation coefficients between monthly anomalies in the cloud cover and the moisture convergence are relatively large and statistically significant. As moisture advection is the most important source of clouds over the Arctic Ocean in winter, the decreasing moisture convergence results in less cloud formation, possibly as a result of weakening cyclonic activity. Less cloud over this region leads to less cloud cover over the central Arctic Ocean in that less cloud is advected westward in the cyclone track. In spring and summer, increasing cloud cover is related to increasing moisture convergence due to increasing cyclonic activity.