The motion of air relative to the Earth's surface. The term usually refers to horizontal air motion, as distinguished from vertical motion, and to air motion averaged over a chosen period of 1–3 min. Micrometeorological circulations (air motion over periods of the order of a few seconds) and others small enough in extent to be obscured by this averaging are thereby eliminated. The choice of the 1- to 3-min interval has proven suitable for the study of the hour-to-hour and day-to-day changes in the atmospheric circulation pattern, and the larger-scale aspects of the atmospheric general circulation.