Inbetween these major cloud bands are two relatively cloud-free areas, one in each hemisphere, where the world's great deserts are found. The polar areas are very different in terms of cloudiness. Whereas the North Pole is surrounded by the Arctic Ocean, the South Pole is near the middle of Antarctica and is less cloudy, primarily because the elevated land mass prevents the passage of ocean storms. Antarctica is the driest as well as the coldest continent. The oceans are almost always cloudier than the land masses.
Clouds regulate the Earth's thermostat.
Areas with persistent cloudiness, the northwest U.S. for example, tend to have small temperature variations from day to night. Records from satellite observations indicate that global temperatures are slightly cooler because of clouds. The reason for this is the large amount of cooling that results from the cloud masses found over ocean areas. These clouds are particularly efficient at deflecting incoming sunlight back to space.