Spatiotemporal Structure of decadal scale variability observed in the Global SST and lower-tropospheric circulation fields

The spatiotemporal evolution of decadal scale variability (DSV) is diagnosed by lag-correlation method, using measured sea surface temperature (SST) and geopotential height at 850 hPa (Z850) of the NCEP/NCAR reanalysis for about 50 years. Three typical DSVs were identified in the global SST and Z850 fields, i.e., the DSV over the Pacific being concurrent with the decadal modulation of the El Nino/Southern Oscillation (EDSV), the local DSV in the mid North Pacific (LDSV), and the DSV associated with the North Atlantic Oscillation (NAO) (NDSV).

EDSV covers almost the entire Pacific with a symmetric structure with respect to the equator. Associated SST fluctuations are in-phase in the tropical central-eastern Pacific, off the western coast of the North and South American continents and in high latitudes, while they are out-of-phase in the subtropics around 30° latitude in both hemispheres. The evolution is maintained by the interaction with development of subtropical highs and anomalous depression around the Indonesian maritime continent. The former forcing the trades tends to occur prior to the latter representing the anomalous Walker circulation. LDSV is characterized by a much more localized oscillation along the subarctic frontal zone in the North Pacific, moving eastward accompanied by the atmospheric anomalies. NDSV is confined to the North Atlantic and excited by the standing evolution of NAO. The atmospheric variability tends to precede the oceanic one.