Classification of 500 mb patterns related to the abnormal january 1963

Abstract

Classification of daily 500 mb patterns in 10 winters into fundamental and sub-weather types is carried out by using the eccentric index newly defined in the present study. One of the fundamental weather types, L1-type, is circulation patterns similar to those observed in the abnormal January 1963. The eccentric index, anomaly of the zonal index and the anomaly of the amplitude of the third harmonic at 50°N classify nine fundamental weather types into twenty-seven sub-weather types. 500 mb patterns in January 1963 is more similar to L11-type, one of the sub-weather types, than to L1-type. The anomaly of the amplitude of the firs t harmonic at 50°N is positively correlated to the eccentric index and related also to the eccentricity of the circumpolar westerlies. These results are explained synoptically and the usefulness of the eccentric index is shown. The statistical behavior of the zonal index is analyzed in connection with the fundamental weather types. From this statistical behavior and the correlation field between the zonal index and the anomaly of 500 mb heights, we come to the conclusion that the eccentric index selects circulation patterns with the severe high and low index. In other words, there are circulation patterns in which the severe high or low index stages are apt to occur. The large-scale cut-off low which often develops in the Pacific in one of the sub-weather types and the characteristics of the phase angle of the fourth harmonic at 50°N are also discussed. L1-type is observed very often in winter 1952-53 and persistently in January 1963. These facts suggest that L1-type is very important to the climatic variation causing abnormal weather simultaneously in several regions in the northern hemisphere. The categories presented here are compared with those obtained by other authors. Some of the weather types presented by HESS and BREZOWSKY (1952) correspond to the present author's, and the wind direction and temperature observed at Zurich are related to the fundamental weather types. Severe cold in North Japan is connected with the present classification. © 1964, Japan Meteorological Agency. All rights reserved.