Dear Tom,
Why is it usually more cloudy in the autumn than in the summer?
Roger Hohman
Dear Roger,
The difference in the amount of heat provided by sunlight is the fundamental cause of seasonal variations in cloudiness.
In the warm season, the nearly overhead sun strongly heats the ground and overlying air. Currents of ascending warm air give rise to cumulus clouds that grow vertically into local cloud patches rather than spreading horizontally into widespread overcasts.
The opposite process prevails in the autumn and winter. Sunshine strikes the ground at a small angle and delivers little heat. The atmosphere grows colder, and the coldest layer is at ground level. Colder air under warmer is stable, and condensation and cloudiness tend to be horizontally stratified, resulting in widespread and long-lasting overcasts.
Why is it usually more cloudy in the autumn than in the summer?
Roger Hohman
Dear Roger,
The difference in the amount of heat provided by sunlight is the fundamental cause of seasonal variations in cloudiness.
In the warm season, the nearly overhead sun strongly heats the ground and overlying air. Currents of ascending warm air give rise to cumulus clouds that grow vertically into local cloud patches rather than spreading horizontally into widespread overcasts.
The opposite process prevails in the autumn and winter. Sunshine strikes the ground at a small angle and delivers little heat. The atmosphere grows colder, and the coldest layer is at ground level. Colder air under warmer is stable, and condensation and cloudiness tend to be horizontally stratified, resulting in widespread and long-lasting overcasts.
