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Circulation epochs in the 20th century and variation of the types of atmospheric circulation in Poland
Języki publikacji
Abstrakty
A brief survey of classifications of the circulation epochs, ie. Periods of time when definite macro-forms of circulation prevail over the Northern Hemisphere, were included in this paper. All classifi-cations refer to the period from the end of XIXth century to the last decade of XXth century. Authors present conception of such classification procedure for the period 1901-1998 on the basis of mean seasonal values of the Zonal Index (ZI), assessing circulation conditions between the 350 and 650 N and seasonal values of the NAO. By means of the Ward's clustering method we were able to distinguish four groups of years within which: strong zonal flow prevails during the whole year (A), strong zonal flow dominates only in winter (B), weak zonal circulation affects only winter conditions (C) and weak zonal flow consti-tutes the characteristic feature of the circulation condition during the whole year (D). The occur-rence of the years classified as type B and C was particularly useful and allowed us to distinguish 7 circulation epochs. Definite seasonal patterns of intensity of the zonal flow expressed by values of the ZI and the NAO were ascribed to this epochs. During the epoch of 1987-1998 the strongest zonal circulation prevailed, whereas the least intense zonal flow occurred from 1957 to 1970. The changes in frequency of circulation types in Poland (according to Osuchowska-Klein, 1978, 1991) with reference to hemispheric circulation epochs were analysed. On the whole, considerable increase in ration between western and eastern types of circulation during the period of 1987-1998 and 1911-1927 is observed however during the epoch of 1971-1986 eastern types dominate.
Czasopismo
Rocznik
Tom
Strony
221--239
Opis fizyczny
tab., wykr., bibliogr. 42 poz.
Twórcy
Bibliografia
Typ dokumentu
Bibliografia
Identyfikator YADDA
bwmeta1.element.baztech-article-BUS1-0006-0059
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