FUZZY RULE-BASED CLASSIFICATION OF ATMOSPHERIC CIRCULATION PATTERNS

A fuzzy rule-based methodology is applied to the problem of classifyin g daily atmospheric circulation patterns (CP). The purpose of the appr oach is to produce a semi-automated classification that combines the e xpert knowledge of the meteorologist and the speed and objectivity of the computer. Rules are defined corresponding to the geographical loca tion of pressure anomalies. A CP is described by the location of four different possible pressure anomalies. The rules are formulated with f uzzy sets, allowing a certain flexibility because slightly different p ressure maps may correspond to a given CP. Accordingly the degree of f ulfilment of a rule is defined in order to measure the extent to which a pressure map may indeed belong to a CP type. As an output of the an alysis, the CP on any given day is assigned to one, and only one, CP t ype to a varying degree of credibility. The methodology is applied to a European case study. The subjective classification of European CPs g iven by Hess and Brezowsky provides a basis for constructing the rules . The classification obtained can be used, for example, to simulate lo cal precipitation conditioned on the 700 hPa pressure field. The infor mation content of the fuzzy classification as measured by precipitatio n-related indices is similar to that of existing subjective classifica tions. The fuzzy rule-based approach thus has potential to be applicab le to the classification of GCM produced daily CPs for the purpose of predicting the effect of climate change on space-time precipitation ov er areas where only a rudimentary classification exists or where none at all exists.