Seasonality of the Lagged Relationship between ENSO and the Northern Hemispheric Polar Vortex Variability

This paper reports the seasonal feature of the relationship between ENSO and the stratospheric Polar Vortex Oscillation (PVO) variability in the Northern Hemisphere. It is shown that the lagged ENSO-PVO coupling relationship exhibits distinct seasonal feature, due to the strong seasonality of PVO and ENSO. Specifically, the PVO variability not only during winter, but also in autumn and spring months, is significantly correlated with ENSO anomalies leading by seasons; however, no significant effect of ENSO is found on the PVO variability in winter months of November and February. Although a significant ENSO effect is primarily observed when ENSO leads PVO by about one year, a significant correlation is also found between PVO in the following spring months (M+1A+1) and ENSO anomalies in the previous autumn (A-1S-1O-1N-1) when ENSO anomalies lead by about 18 months. The significant correlation between PVO in various seasons and the corresponding ENSO anomalies leading by seasons could be explicitly verified in most of the individual years, confirming that the lagged ENSO effect can largely modulate the seasonal timescale variability of PVO. Moreover, the composite spatial patterns of the zonal-mean temperature anomalies further show that the ENSO effect on the PVO in various seasons is related to the interannual variability of the seasonal timescale PVO events.