- Rossby wave
Rossby (or planetary) waves are giant
meandersin high-altitude winds that are a major influence on weather. Their emergence is due to shear in rotating fluids, so that the Coriolis forcechanges along the sheared coordinate. In planetary atmospheres, they are due to the variation in the Coriolis effectwith latitude. The waves were first identified in the Earth's atmospherein 1939by Carl-Gustaf Arvid Rossbywho went on to explain their motion. Rossby waves are a subset of inertial waves.
The special identifying feature of the Rossby waves is its
phase velocity(that of the wave crests) always has a westward component. However, the wave's group velocity(associated with the energy flux) can be in any direction. In general: shorter waves have an eastward group velocity and long waves a westward group velocity.
The terms "
barotropic" and " baroclinic" Rossby waves are used to distinguish their vertical structure. Barotropic Rossby waves do not vary in the vertical, and have the fastest propagation speeds. The baroclinic wave modes are slower, with speeds of only a few centi metres per secondor less.
northern hemisphere's jet streamdeveloping (a, b) and finally detaching a "drop" of cold air (c). Orange: warmer masses of air; pink: jet stream.] Rossby waves in the atmosphereare easy to observe as (usually 4-6) large-scale meanders of the jet stream. When these loops become very pronounced, they detach the masses of cold, or warm, air that become cyclones and anticyclones and are responsible for day-to-day weather patterns at mid-latitudes.
The wave speed is given by
where "c" is the wave speed, "u" is the mean westerly flow, "" is the
Rossby parameter, and "k" is the total wavenumber.
Rossby parameteris defined::"φ" is the latitude, "ω" is the angular speedof the Earth's rotation, and "a" is the mean radius of the Earth.
Oceanic Rossby waves are thought to communicate climatic changes due to variability in
forcing, due to both the windand buoyancy. Both barotropic and baroclinic waves cause variations of the sea surface height, although the length of the waves made them difficult to detect until the advent of satellite altimetry. Observations by the NASA/ CNES TOPEX/Poseidon satelliteconfirmed the existence of oceanic Rossby waves [Chelton, D. B., and M. G. Schlax. 1996. "Global observations of oceanic Rossby waves." . 272:234-38 (12 April 1996)]
Baroclinic waves also generate significant displacements of the oceanic
thermocline, often of tens of meters. Satellite observations have revealed the stately progression of Rossby waves across all the ocean basins, particularly at low- and mid-latitudes. These waves can take months or even years to cross a basin like the Pacific.
* Rossby, C-G (1939), Relation between variations in the intensity of the zonal circulation of the atmosphere and the displacements of the semi-permanent centers of action, "J. Marine Research" pp38-55
* Platzman, G (1968) The Rossby wave, "Quart. J. Roy. Meteorol. Soc." pp94-248
* Dickinson, R E (1978) Rossby waves - long-period oscillations of oceans and atmospheres, "Ann. Rev. Fluid Mech." pp10-195
* [http://amsglossary.allenpress.com/glossary/search?p=1&query=Rossby+wave&submit=Search Rossby Waves, from the American Meteorological Society]
* [http://www.noc.soton.ac.uk/JRD/SAT/Rossby/Rossbyintro.html An introduction to oceanic Rossby waves and their study with satellite data]
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