[A-CG33] Multi-scale ocean-atmosphere interaction in the tropics

[ACG33-P01] ENSO and Tropical Pacific Decadal Variability forced and unforced by extratropical SST variability

*Yu Kosaka¹, Masaki Toda¹ (1.Research Center for Advanced Science and Technology, University of Tokyo)

El Niño-Southern Oscillation (ENSO) and Tropical Pacific Decadal Variability (TPDV) affect the global climate. In the present study, we examine ENSO and TPDV that are forced and unforced remotely by extratropical SST variability. We use the extratropical ocean-global Atmosphere (XTOGA) ensemble pacemaker simulations based on GFDL CM2.1, where extratropical SST anomalies are restored toward observations. Its ensemble mean variability represents those forced by the extratropical influence, whereas the inter-member variability is regarded as those arising from internal variability within the tropics. Prescribing SST poleward of 15 degrees latitude in the Pacific strongly constrains the Nino3.4 SST, with the correlation with observations reaching 0.78 in January. This extratropical pacemaker effect remains, although weaker, if the restoring region is limited to poleward of 25º latitudes. The tropical internal ENSO tends to show a biennial tendency compared with the extratropically-driven ENSO. These results suggest the importance of influence from (or interaction with) the subtropical and midlatitude SST variability for tropical Pacific variability.