Like the ocean, the earth’s atmosphere is a fluid (it flows). And like the ocean, the atmosphere has currents.
Currents in the atmosphere are effected by two main factors.
The first is solar radiation. The solar heating of the atmosphere is uneven for many reasons, but the two main reasons are the angle of the earth’s surface to the sun’s radiation and earth’s rotation. The heat absorbed by the earth’s surface is most significant at the equator and least significant at the poles. The earth’s rotation means there is daytime heating and nighttime cooling. As fluids, both the oceans and the atmosphere are continuously compensating for the resulting temperature differentials. As a result, we have the wind, the ocean currents and a rivers of air in the atmosphere called the jet streams.
As the atmosphere heats up at the equator, the air becomes less dense and rises. The less dense air is replaced by denser air moving in from the south and from the north. The resulting circulation in the atmosphere is called the “Hadley Cell”.
The resulting surface winds in the tropics (northern hemisphere) are typically northerly and are deflected to the west by the Coriolis effect.