Cloud Altitudes

Having been raised in Nevada, I grew accustomed to the sight of white, puffy clouds drifting high in a dark blue sky. When I settled in Alaska, I was perplexed because the sky didn't seem as blue or the clouds so high.

Relative elevation explained one of the differences. Nevada is at an average elevation of about 5000 feet, while Fairbanks is only at about 500. The intervening layers of atmosphere at lower elevations effectively dull the brilliant blue seen in the mountains where the air is thinner.

But this still did not explain why the clouds seem so much lower. Common sense would seem to dictate that if the ground elevation were lower, the clouds should seem even higher.

The fact is that normal clouds in the Arctic actually do occur lower than they do further south. That portion of the earth's atmosphere in which weather occurs is called the troposphere. As the earth spins on its axis, the troposphere bulges out at the equator due to centrifugal effects. The difference in thickness of the troposphere with latitude is truly significant. At the equator, it rises to a height of about 13 miles, at the poles, it is only about 5 miles thick. So clouds associated with weather actually do ride closer to the earth's surface at higher latitudes.

Paradoxically, the bulge caused by the earth's rotation means that the roof of the troposphere at the equator is colder--about -110°F--than it is at the poles, where it averages a relatively balmy -60°F.