Rossby wave

Earth's rotation affects moving air and water through the Coriolis effect, which varies with latitude. In a rotating fluid, this variation helps generate and restore broad north–south displacements, producing planetary-scale waves. In an idealized atmospheric setting, a Rossby wave travels westward relative to the mean flow; the background wind can carry the overall pattern eastward or alter its motion. Actual waves are shaped by complex flows, topography, stratification and interactions with other atmospheric or oceanic processes.

In the atmosphere, Rossby waves appear as large-scale undulations in the westerly circulation and are associated with ridges and troughs in the upper-level flow, including the jet-stream region. Their position and movement influence the paths of weather systems and the exchange of air between lower and higher latitudes. When a wave pattern moves slowly, weather conditions beneath it can persist, although a Rossby wave alone does not determine whether a particular extreme event occurs. The contribution of specific mechanisms to extreme weather remains an active subject of research.

Oceanic Rossby waves are not the familiar short surface waves that break on beaches. They extend over very large distances, move slowly, and often have only a small surface-height signal. Their effects are more pronounced beneath the surface, including in the thermocline, the transition between warmer surface water and colder deep water. Satellite radar altimeters can measure sea-surface height over broad areas, allowing researchers to identify these waves and follow changes in ocean circulation.

C. G. Rossby developed the theory of planetary-scale atmospheric motion in the 1930s, and oceanographers later identified Rossby-wave signals in thermal and satellite sea-level observations. NASA's account of ocean observations describes how TOPEX/Poseidon, launched in 1992, made globally distributed sea-level measurements that helped reveal basin-scale wave patterns. These waves matter because they are part of the atmosphere–ocean circulation system and can transport or redistribute energy and influence currents. Their speed and effects depend on the setting, so simple idealized formulas should not be treated as exact descriptions of every observed wave.