Sustained winds are caused by differences in the atmospheric pressure. When a difference in atmospheric pressure exists, air moves from the higher to the lower pressure area, resulting in winds of various speeds. On a rotating planet, such as Earth, the air will also be deflected by the Coriolis effect, except exactly on the equator.
https://cimss.ssec.wisc.edu/satmet/modules/7_weather_forecast/images/pressurewind.gif
Latest Answers