I Didn’t Know That...

Q: Is it true that there are “deserts” in the oceans, places where little or no rain falls?

A: Yes, according to atmospheric scientist Joel Norris of the Scripps Institution of Oceanography. The “deserts” exist because of circulatory patterns in the atmosphere, particularly the Hadley circulation, in which warm air rises near the equator, flows outward toward the poles at upper levels, sinks down to the surface over the subtropics, and returns to the equator in the form of trade winds. The air that rises near the equator loses most of its moisture before it reaches the upper levels. But the sinking air over the subtropics prevents subtropical clouds from getting big enough to produce much rain. Very little rainfall thus occurs over ocean or land between 10 degrees and 30 degrees north and south of the equator. Most of the world’s major deserts lie within these latitudes. The poleward ends of these zones were known as the horse latitudes or doldrums, where sailing ships could be becalmed and run out of water. Horses being traded between Europe and the Americas were sometimes thrown overboard to conserve water for the crew.