SSS 2008-08-25

（单词翻译）

This is Scientific American's 60-Second Science. I'm Steve Mirsky . Got a minute?

For accurate weather forecasting and climate analysis, researchers need the best models possible about how the air circulates above the earth. And a new study is challenging the conventional picture of the planet’s air movements. Previous theories pointed¹ to two large circular systems—air rises at the warm equator and then travels toward either pole, where it chills and falls. But the new study posits² that there are actually four distinct air masses, two north of the equator and two south. The work appears in the August 21st issue of the journal Science.

In this new view, air again rises at the equator, but falls in the subtropics, making the first cell. The second cell consists of air rising in the middle latitudes—about 30 to 60 degrees north and south—and then falling again near the poles. The study says that this second cell of rising air accounts for temperatures, winds and moisture levels in the mid-latitudes. Water vapor³ is a major driver of weather events in the tropics. Turns out it may be just as important for weather—and climate—farther north and south.

Thanks for the minute for Scientific American's 60-Second Science. I'm Steve Mirsky.