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 three days to a month and is often associated with a warm anticyclone in high latitudes and cold cyclonic circulation in lower latitudes.
Fig. 1provides a sequence of the 1,000-500-mb thickness charts that illustrates the change from high-index zonal circulation to meridional circulation to the low-index pattern in...
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References
McIntosh, D. H., and A. S. Thom, 1973. Essentials of Meteorology. London: Wykham Publications.
Mullen, S. L., 1983. Computer simulation of atmospheric “blocking,” Weatherwise 36(5), 232–233.
Stringer, E. T., 1972. Foundations of Climatology. San Francisco: W. H. Freeman.
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© 1987 Van Nostrand Reinhold
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Oliver, J.E. (1987). Blocking . In: Climatology. Encyclopedia of Earth Science. Springer, Boston, MA. https://doi.org/10.1007/0-387-30749-4_27
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DOI: https://doi.org/10.1007/0-387-30749-4_27
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