Trade Winds also move from east to west in the southern hemisphere, i.e, southeast to northwest, as described above.

The trade winds originate in the vicinity of 30 degrees north and south latitude, in bands of elevated atmospheric pressure known as the subtropical highs.

The warm air at the equator rises to the tropopause and heads poleward and eastward. By the time the air gets to about 30 degrees from the equator it begins to cool and descend, and converges, since there is less room than at the equator, so the air pressure builds. Some of the air near the surface heads toward the equator and the cycle begins again. This large-scale north-south circulation comprises one cell of the three-cell model of general atmospheric circulation.

The air moves west as it goes south due to conservation of momentum. The circumference of the earth, measured along lines of latitude, is greater at the equator than at 30 degrees (or elsewhere). A parcel of air that was still at some latitude above the equator, i.e. moving at the same speed as the surface of the earth, would end up over a longitude west of where it started as it moved south, since to stay over the same latitude it would have to speed up somehow to cover the greater east-west distance. This is also why air moving poleward also travels east relative to the surface - it is going faster relative to the surface at higher latitudes than it was at lower latitudes.