Global air circulation is the way that the planet distributes the heat it receives from the Sun across its surface. The single cell model of atmospheric circulation was developed in the 18th century. It states that air circulates from the equator to the poles and back again in a single loop in each hemisphere. But this is way too oversimplified and does not take several factors into account including the rotation and tilt of the planet. There are actually three major wind cells, hence the three cell model. There is the tropical cell, the midlatitude cell, and the polar cell for each hemisphere. These cells give rise to the trade winds near the equator, the westerly winds between the equator and the poles, and the polar easterly winds near the poles. This also accounts for low wind areas between these wind belts including the equatorial doldrums and the horse latitudes. Even the three cell model is simplified from the realities of global air circulation but it does account for these major features.