Rossby waves Named after the Swedish-American meteorologist C. -G. Rossby (1898–1957), Rossby waves are equatorward troughs and poleward ridges forming long waves in the circumpolar flow of the upper air, particularly in the mid and upper troposphere, with a typical wavelength of around 2000 km. Three or four waves usually occur in the circumpolar westerly wind flow over mid latitudes. They may remain stationary (as standing waves) when wind speed and wavelength have a given relationship. The waves may be initiated by lower winds over mountain barriers, e.g. the Rocky Mountains, or by heating over warm oceans in winter or over land in summer. They are then amplified by vorticity (due to the Earth's rotation) in anticyclonic curvature (in ridges) and in cyclonic curvature (in troughs). Characteristic positions for the main troughs in the upper westerlies over the northern hemisphere are about 70° W and 150° E. The Rossby waves influence the formation of surface depressions which tend to develop on a frontal wave ahead of an upper trough. Rossby waves also occur in the oceans.

Rossby waves Troughs extending towards the equator and ridges extending towards the poles that form long waves in the circumpolar flow of the upper air, particularly in the mid and upper troposphere, with a typical wavelength of around 2000 km; in the northern hemisphere the main troughs are characteristically at about 70°W and 150°E and three or four waves usually occur in the circumpolar westerly wind flow over mid-latitudes. The Rossby waves influence the formation of surface depressions which tend to develop on a frontal wave ahead of an upper trough. They are named after the Swedish-American meteorologist C. G. Rossby (1898–1957).