> as far as I know it's not a lack of water but what happens to the water once it's evaporated that causes the dryness in those areas - it goes up into the high

> as far as I know it's not a lack of water but what happens to the water once it's evaporated that causes the dryness in those areas - it goes up into the high atmosphere and comes down in rain over the tropics. Wish I remembered the name though. It's the other way around - the subtropical ridges are high pressure high altitude masses of dry air that fall to the surface around 30 N & S. This dry air is then sucked back to the equator as the Trade Winds, which further dry out the sub tropics. > Wish I remembered the name though. Hadley cell?