A comment about the seasonal cycle of cloud cover

The most striking feature of low cloud cover during the winter months is the relative maximum over the northern North Atlantic. This manifests the uplift of air masses by the frequent cyclone activity in this area associated with the Icelandic Low. Low cloud cover is rather limited over central and eastern Siberia because of the general subsidence (downward motion) of air in the area of the strong Siberian high. During summer, the Icelandic Low and Siberian High weaken. Low cloud cover becomes more uniform, but with a distinct increase over the Arctic Ocean. The increase reflects the dominance of low-level stratus, which form as warm air masses moving over the ocean are chilled by the cold, melting sea ice cover. Then autumn months illustrate the transition back to the winter pattern. Total cloud cover combines low, middle and high clouds. While amounts of total cloud are hence greater than for only low cloud, it can be seen that most cloud cover is of the low variety.