Fuzzy logic circulation types based on the Osuchowska-Klein classification system created for Poland

Abstract

Fuzzy logic was applied as a methodology to create an objective calendar of daily atmospheric circulation based on an existing atmospheric circulation classification system for Poland called the Osuchowska-Klein method, which includes 13 circulation patterns. In this study, circulation patterns given by Osuchowska-Klein were expressed as normalized values of sea level pressure in a regular 5° × 5° grid over the area of interest. Cases of daily atmospheric circulation (i.e., normalized values for the same domain) observed from January 1948 to December 2007 were defined in the same manner. The pattern-matching procedure employed in the study was made objective with the application of fuzzy logic sets in a few steps as follows: (1) discrimination and grouping of grid points as well as their classification in order to clearly define each Osuchowska-Klein circulation pattern, (2) calculation of the similarity between observed normalized pressure and that of the pattern at each selected grid point using a membership function, (3) determination of the degree of fulfillment for every class of grid points, (4) determination of the degree of a case and pattern, (5) selection of the circulation type for a particular day based on the degree of fulfillment for each pattern. The largest value of the degree of fulfillment indicates the type of circulation pattern on any given day. Finally, a validation of the obtained results is discussed. This was accomplished using the chi-square test and a comparison of consistency between the traditional and objective approach types. The results do show some differences between the subjective and objective methods, however, they are not major differences, especially when taking into account the fact that the two methods are quite different, as well as the complex nature of pressure systems.