Delayed Tropospheric Response over the East Asia–Northwest Pacific Sector to Arctic Stratospheric Polar Vortex Intensity Anomalies
Abstract
Based on ERA5 reanalysis data (1979–2022) and sensitivity experiments with the WACCM climate model, this study examines the delayed tropospheric response over the East Asia–Northwest Pacific (EANP) region to stratospheric polar vortex intensity (PVI) anomalies. It is found that positive PVI anomalies in the lower stratosphere from mid-December to late February show relatively weak concurrent effects on the EANP troposphere but are followed by a pronounced circulation response in March. This delayed response features positive geopotential height and temperature anomalies north of 50°N, and negative anomalies between 30°N and 50°N. It cannot be explained by low-frequency drivers such as ENSO, the QBO, Arctic sea ice, or diabatic processes, and primarily reflects low-frequency adiabatic evolution. In particular, positive PVI anomalies peaking in January are followed by negative stratospheric potential vorticity tendencies over high latitudes in February, favoring positive height anomalies in the underlying troposphere. Subsequently, enhanced southward propagation and convergence of upper-tropospheric synoptic eddies over the EANP region further amplify a meridional dipole circulation in March. Nudging experiments confirm that January PVI anomalies alone are sufficient to trigger this delayed patterns. These results suggest that January PVI anomalies could provide a longer lead-time source of predictability for tropospheric circulation over the EANP than in other extratropical areas.