Wind, air in motion. The term is usually applied to the natural horizontal motion of the atmosphere; motion in a vertical, or nearly vertical, direction is called a current. Winds are produced by differences in atmospheric pressure, which are primarily attributable to differences in temperature. Variations in the distribution of pressure and temperature are caused largely by unequal distribution of heat from the sun, together with differences in the thermal properties of land and ocean surfaces . When the temperatures of adjacent regions become unequal, the warmer air tends to rise and flow over the colder, heavier air. Winds initiated in this way are usually greatly modified by the earth's rotation .
