Cold air at the ground of the equator is heated by solar irridiance and mounts to higher levels. The caused underpressure at the ground pulls colder air from regions with higher air pressure and closes the circle of a Hadley Cell. The Hadley Celly, north and south of the equator generate a steady brise called Passat (lit. Trade Winds).
North and South of the Hadley Cells are Ferrel Cells who cause irragular and stormy wind conditions. The Polar Cells again generate quite steady and stable winds. 1998 one of the first World Wind maps for measured windspeed at 10m height was published.
The various wind conditions demand different technologies to harvest the maximum of the energy and secure the Wind turbine from extreme wind speeds.