Wind is the horizontal movement of air. Every single wind is generated by the uneven heating of Earth's surface, which triggers convection currents in motion. Convection currents on a huge level cause global winds; convection currents on a small scale cause local winds. The global wind prototype is also known as the "General Circulation" and the surface winds of each hemisphere are divided into three wind belts, those are, “Polar Easterlies” from 60-90 degrees latitude, “Prevailing Westerlies” from 30-60 degrees latitude and “Tropical Easterlies” or “Trade Winds” from 0-30 degrees latitude.