in meteorology, large horizontal atmospheric undulation that is associated with the polar-front jet stream and separates cold, polar air from warm, tropical air. These waves are named for Carl-Gustaf Arvid Rossby (Rossby, Carl-Gustaf Arvid), who first identified them and explained their movement.

Rossby waves are formed when polar air moves toward the Equator while tropical air is moving poleward. Because of the temperature difference between the Equator and the poles due to differences in the amounts of solar radiation received, heat tends to flow from low to high latitudes; this is accomplished, in part, by these air movements. Rossby waves are a dominant component of the Ferrel circulation (Ferrel cell). The tropical air carries heat poleward, and the polar air absorbs heat as it moves toward the Equator. The existence of these waves explains the low-pressure cells (cyclones (cyclone)) and high-pressure cells (anticyclones (anticyclone)) that are important in producing the weather of the middle and higher latitudes.