Study of Year-to-Year Variations in Seasonal Progression over Japan Using Frontal Zone Indices

The purpose of this work is to create indices to represent the atmospheric conditions throughout Japan based on frontal zone data at 5-day intervals for the period 1948-2013. The index was created by conducting principal component analyses of the distribution of frontal frequencies near frontal zones. The distribution of the factor loadings were interpreted as variations of the frontal zone in the following manner: PC1, northward/southward shift of the frontal zone; PC2, increase/decrease of frontal frequencies near the frontal zone; PC3, the extending direction of the frontal zone, whether northwest-southeast or southwest-northeast; and PC4, west-east variations of the frontal frequencies near the frontal zone. The result of correlation analyses between the indices defined as the factor scores and those representing global climatic and oceanic phenomena or teleconnection patterns revealed, in detail, periods with strong connections and comprehensive relationships reported by previous works. Furthermore, trends were found in the recent climate, such as southward shift of the frontal zones in mid-and late spring and increased frontal frequencies around frontal zones in mid-and late summer.