Abstract/Summary

The Arctic Oscillation (AO) is the most significant mode of sea level pressure (SLP) anomalies in the Northern Hemisphere, exhibiting significant multiple-timescale variability from synoptic to decadal. Using NCEP Climate Forecast System Reanalysis data from 1979 to 2022 during the cold season (November to April), this study identifies the relationship between the number of extra-tropical cyclones entering and exiting the Arctic and the AO synoptic variability. The Joint Net Cyclone Flux (JNCF) is significantly correlated to the spatio-temporal evolution of the synoptic AO and the composites of SLP associated with the JNCF perform AO-like patterns. Subsequent piecewise potential vorticity inversion reveals the impacts of extratropical cyclones on the synoptic-scale AO-like geopotential height anomalies at different altitudes. The effects of extratropical cyclone are more important than the Arctic stratospheric PV intrusion. Furthermore, the upper-level dynamic process among all extratropical cyclone effects dominates the evolution of synoptic-scale AO-like geopotential height anomalies.