基于位涡构建的初夏东北冷涡活动指数及其应用OA

The northeast cold vortex(NECV)is an important synoptic-scale weather system over the mid-to high-latitudes of northeastern Asia.NECV activity not only triggers heavy rainfall and low-temperature disasters in North-east China but also exerts significant influences on weather and climate over broader regions.Constructing an objec-tive cold vortex index is essential for quantitatively characterizing NECV activity.Conventional cold vortex indices are generally derived from geopotential height or temperature over predefined key regions affected by the NECV.In this study,NECV records from 1961 to 2021,together with ERA5 reanalysis data,were used to investigate the struc-tural differences between early-summer(May-June)and midsummer(July-August)cold vortices and to examine the influence of seasonal variations on index construction.Based on these analyses,a new potential vorticity(PV)index was developed using the mean 300 hPa PV averaged over the key early-summer cold vortex region.The pro-posed index effectively characterizes NECV activity.Comparative analyses demonstrate that the PV index outper-forms conventional geopotential height and temperature indices in three major aspects.First,the three indices differ substantially in their ability to characterize NECV activity.For strong and moderate cold vortices,both the PV index and the geopotential height index exhibit satisfactory identification performance,accurately representing their spatial distribution and intensity.In contrast,only the PV index provides reliable identification of weak cold vortices.This advantage is likely attributable to the relatively small geopotential height and temperature anomalies associated with weak cold vortices,which produce only minor fluctuations in indices based on these variables.The PV index is less susceptible to this limitation and therefore more effectively captures weak vortex activity.Second,although all three indices are capable of representing the interannual variability of NECV occurrence frequency,the PV index exhibits superior performance,particularly during years with anomalously frequent NECV activity.In contrast,during years with anomalously weak NECV activity,the three indices show comparable skill.Third,the PV index not only effec-tively quantifies the influence of cold vortices on precipitation over Northeast China but also serves as a robust indi-cator of pre-flood-season rainfall over South China and the Jianghuai region.Years with anomalously high PV index values are characterized by pronounced upward motion and enhanced moisture convergence over South China in May and the Jianghuai region in June,providing favorable dynamical conditions for increased precipitation.The po-tential vorticity-based cold vortex index proposed in this study provides a physically meaningful metric for characte-ring early-summer NECV activity.It provides useful information about the East Asian climate system,contributes to improving climate prediction,and has broad potential for operational applications.However,it is important to note that midsummer cold vortices differ significantly from early-summer cold vortices in both intensity and structural characteristics.Consequently,the index proposed here is not directly applicable to midsummer cold vortices.Further-more,cold vortex-related precipitation accounts for a much smaller proportion of total rainfall during midsummer in Northeast China.Therefore,from the perspective of precipitation analysis alone,developing a dedicated midsummer cold vortex index is of relatively limited practical significance.