Nonwind

Nonwind is a term used in meteorology and related fields to describe a state of the atmosphere in which horizontal wind is effectively absent over a given area and period. It is commonly associated with the meteorological condition known as a calm. The exact threshold for what constitutes nonwind varies, but calm is typically defined by surface wind speeds below about 1.0 meters per second (2.2 mph). The term nonwind is less formal and appears mainly in descriptive or conceptual discussions rather than as an official category in all meteorological agencies.

Causes of nonwind include high-pressure systems with subsiding air that suppresses horizontal flow, temperature inversions that stabilize the lower atmosphere, and local terrain features that disrupt air movement. Nonwind can occur at the surface while winds aloft remain nonzero, due to vertical wind shear or localized circulation patterns.

Effects of nonwind include stagnation of air, increased surface heating, and reduced dispersion of pollutants, odors, or moisture. For sailors and pilots, nonwind conditions influence navigation, engine use, and fuel planning. In agriculture, calm conditions affect evapotranspiration, spraying outcomes, and disease risk.

Frequency and distribution of nonwind vary by region, season, and broader climate patterns. Some areas exhibit predictable diurnal calm periods related to land-sea breezes or persistent high-pressure regimes. Changes in climate variability and atmospheric circulation can alter the frequency of calm conditions, making nonwind a useful descriptor in regional climatology studies.

See also: Calm (weather), wind, meteorology.