An intensity index and its application for summertime extratropical cyclones in East Asia

Abstract

Abstract The intensity definition and classification of the extratropical cyclone (EC) are still less studied than the tropical cyclone, due to the relatively ambiguous structure and diverse life cycle of ECs. In this study, a two-dimensional objective cyclone identification method based on outermost closed isolines is used to obtain the EC-related datasets, and the summertime ECs in East Asia are classified by the relationship between ECs of different intensities and the corresponding precipitation. The results show that compared with the cyclone mean depth, central wind and other traditional intensity indicators, the cyclone intensity index that is the maximum product of the EC-associated wind speed and specific humidity, has the highest correlation with the EC-associated maximum precipitation (r = 0.74). To simplify the definition of cyclone intensity index, the vq max within the radius of 300 km from the cyclone center is defined as the cyclone intensity. According to the relationship between EC and precipitation intensity and the precipitation grades in China, the ECs in East Asia are classified into four levels. Accordingly, the EC-associated maximum precipitation increases substantially with the raising of cyclone level. In particular, 32.8% of heavy rain events in East Asia in summer are related to ECs of the strongest category. The results will facilitate a better understanding of the relationship between the strongest category EC and local precipitation.

Keywords

• Extratropical cyclone
• Objective identification
• Precipitation intensity
• Cyclone classification