A New Definition of the Western Pacific Subtropical High Indexes Based on Three-Pattern Decomposition of Global Atmospheric Circulation

Formation and variation dynamics of western Pacific subtropical high (WPSH) have always been an important subject of interest for Chinese meteorologists. However, geopotential height field indexes commonly used in current studies and operational services cannot accurately describe the evolution characteristics of the subtropical high with a global warming background. It is known that the stream function of horizontal circulation defined by the three-pattern decomposition of global atmospheric circulation can equivalently describe the three-dimensional spatial geometric images of the subtropical high. Based on this information, this study proposes the use of the zero contour of the 500 hPa stream function of horizontal circulation as the objective standard to redefine the area, intensity, ridge line, and westward ridge point indexes of the subtropical high. The objectivity and rationality of the newly defined indexes of subtropical high are verified by taking short-term structural evolution characteristics of the subtropical high during summer in 2018 and its relationship with precipitation in eastern China. Results reveal accurate depiction of the large-scale eddy circulation characteristics of the subtropical high with the use of the newly defined indexes of based on the stream function of the horizontal circulation. Additionally, the dynamic and thermodynamic equations concerning the stream function of three-pattern decomposition of global atmospheric circulation provide a new theoretical tool for studying the mechanism of the evolution of the subtropical high anomaly by using the newly defined indexes.