Middle-latitude circulation is classically represented by belts of high- and low-pressure systems that are approximately parallel to the equator. Winds associated with these systems also have their major components parallel to the equator and are said to be zonal. Periodically, this zonal flow breaks down and wind components perpendicular to the equator become more important. Such flow is said to be meridional. Meridional flow often results from the blocking action of a persistent anticyclone.
Blocking action is a diminution of the zonal circulation at all levels of the troposphere, with retardation of zonal flow tending to spread westward. The phenomenon may last from 3 days to a month and is often associated with a warm anticyclone in high latitudes and cold cyclonic circulation in lower latitudes. It may result in significant temperature and precipitation anomalies.
Various types of blocking patterns have been recognized. The most common is the omega block, resembling the Greek...
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Bibliography
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Centers of Action
Jet Streams
Reanalysis Projects
Rossby Wave/Rossby Number
Zonal Index
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Oliver, J.E. (2005). Blocking. In: Oliver, J.E. (eds) Encyclopedia of World Climatology. Encyclopedia of Earth Sciences Series. Springer, Dordrecht . https://doi.org/10.1007/1-4020-3266-8_31
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