[ACG34-P08] Relative contribution of remote influence from tropics and extra-tropical oceanic variability on the interannual-to-decadal variability of the midlatitude atmosphere
Keywords:Atmospheric bridge , Western boundary current, Pacific North American pattern , ensemble AGCM simulations
Focusing on the wintertime geopotential height at 500 hPa (Z500), the simulated total variance of Z500 across all ensemble members in GOGA represents the spatial pattern of observed variance well, although the amplitude is underestimated. Among the three geographical centers of large Z500 variance, the North Pacific is marked as a region of the largest forced variance of Z500 in the GOGA ensemble mean, largely due to the well-known atmospheric bridge from tropics. More interestingly, the forced variance of Z500 in GOGA is larger than that in TOGA, suggestive of a role of extra-tropical SST or SIC in enhancing the variance. Also, the atmospheric bridge from tropics into extra-tropics appears to be modulated by extra-tropical SST. Specifically, the Pacific North American pattern-like Z500 anomalies associated with Nino3.4 index is stronger (weaker) during the period when the Kuroshio Extension is stable (unstable). We will discuss to what extent the atmosphere responds to extratropical SST and SIC variability and how such extratropical effects interfere with the remote influence from tropics on the midlatitude atmosphere.