State-dependent atmospheric noise associated with ENSO

A strong relationship between ENSO ( El Nino/Southern Oscillation) and atmospheric short-term variability in the near-surface zonal wind is reported in the present study. On one hand, anomalies in the variance of the short-term atmospheric variability over the western Pacific tend to lead El Nino development. On the other hand, the activity of the fast atmospheric variability over the central Pacific is simultaneously correlated to the NINO3.4 SST. The significant correlation exists over the broad range of atmospheric variability from the synoptic time scale to the inter-seasonal time scale. This finding supports the notion that the ENSO-state dependence of the atmospheric variability serves as a source of stochastic forcing for ENSO. Furthermore, it is demonstrated that there is a significant interdecadal change in this dependence. The state-dependent noise becomes much stronger in the recent period, which possibly explains the recent increase of the ENSO activities, consistent with the recent theory of noise-induced destabilization effect for ENSO.