New look on the classification of atmospheric circulation types by J. Lityński

There are many classifications of atmospheric circulation types. In Poland, the most important one, used in climatological studies, is the classification of circulation types developed by Lityński. This study aims to compare the results of two variations of this classification: the “old” one – based on the NCEP/NCAR reanalysis data and on the original limits of the classes (of indicators Ws, Wp and Cp) proposed by the author of the original classification and the “new” one – which also calculates the limits of the classes on the basis of NCEP/NCAR reanalysis material, but with increasingly longer periods each year. In the period 1971–2015 more than 21% of the results of the “new” classification were different from the “old” one. The differences in the frequency of each class (in relation to individual circulation indicators) in the “old” classification were much higher than in the “new” one. Consequently, the use of “new” limits of the classes causes that in the circulation types catalog the division of the distribution of the Ws, Wp and Cp indicators into three classes is more similar to the one of equal-probability. In the second part of the paper, a modification of the “new” classification isproposed. The “new modified” classification, takes into account only the 30 last years while calculating the limits of the classes. Shortening the period based on which the limits of the classes are calculated one can capture long-term variations in the values of individual circulation indicators, and thus the division of their distributions into three classes is even closer to the equal-probability one.

There are many classifications of atmospheric circulation types. In Poland, the most important one, used in climatological studies, is the classification of circulation types developed by Lityński. This study aims to compare the results of two variations of this classification: the “old” one – based on the NCEP/NCAR reanalysis data and on the original limits of the classes (of indicators Ws, Wp and Cp) proposed by the author of the original classification and the “new” one – which also calculates the limits of the classes on the basis of NCEP/NCAR reanalysis material, but with increasingly longer periods each year. In the period 1971–2015 more than 21% of the results of the “new” classification were different from the “old” one. The differences in the frequency of each class (in relation to individual circulation indicators) in the “old” classification were much higher than in the “new” one. Consequently, the use of “new” limits of the classes causes that in the circulation types catalog the division of the distribution of the Ws, Wp and Cp indicators into three classes is more similar to the one of equal-probability. In the second part of the paper, a modification of the “new” classification isproposed. The “new modified” classification, takes into account only the 30 last years while calculating the limits of the classes. Shortening the period based on which the limits of the classes are calculated one can capture long-term variations in the values of individual circulation indicators, and thus the division of their distributions into three classes is even closer to the equal-probability one.