Observed Influence of North Pacific SST Anomalies on the Atmospheric Circulation

Abstract

A lagged maximum covariance analysis (MCA) of monthly anomaly data from the NCEP-NCAR reanalysis shows significant relations between the large-scale atmospheric circulation in two seasons and prior North Pacific sea surface temperature (SST) anomalies, independent from the teleconnections associated with the ENSO phenomenon. Regression analysis based on the SST anomaly centers of action confirms these findings. In late summer, a hemispheric atmospheric signal that is primarily equivalent barotropic, except over the western subtropical Pacific, is significantly correlated with an SST anomaly mode up to at least 5 months earlier. Although the relation is most significant in the upper troposphere, significant temperature anomalies are found in the lower troposphere over North America, the North Atlantic, Europe, and Asia. The SST anomaly is largest in the Kuroshio Extension region and along the subtropical frontal zone, resembling the main mode of North Pacific SST anomaly variability in late winter and spring, and it is itself driven by the atmosphere. The predictability of the atmospheric signal, as estimated from cross-validated correlation, is highest when SST leads by 4 months because the SST anomaly pattern is more dominant in the spring than in the summer. In late fall and early winter, a signal resembling the PacificNorth American (PNA) pattern is found to be correlated with a quadripolar SST anomaly during summer, up to 4 months earlier, with comparable statistical significance throughout the troposphere. The SST anomaly changes shape and propagates eastward, and by early winter it resembles the SST anomaly that is generated by the PNA pattern. It is argued that this results via heat flux forcing and meridional Ekman advection from an active coupling between the SST and the PNA pattern that takes place throughout the fall. Correspondingly, the predictability of the PNA-like signal is highest when SST leads by 2 months. In late summer, the maximum atmospheric perturbation at 250 mb reaches 35 m K Ϫ1 in the MCA and 20 m K Ϫ1 in the regressions. In early winter, the maximum atmospheric perturbation at 250 mb ranges between 70 m K Ϫ1 in the MCA and about 35 m K Ϫ1 in the regressions. This suggests that North Pacific SST anomalies have a substantial impact on the Northern Hemisphere climate. The back interaction of the atmospheric response onto the ocean is also discussed.

On the Predominant Nonlinear Response of the Extratropical Atmosphere to Meridional Shifts of the Gulf Stream

“…The lag is explained by the adjustment time scale of the GS position to the NAOdriven wind stress and wind stress curl (Gangopadhyay et al 1992). However, Frankignoul et al (2001) found no evidence that the GS SST anomaly exerts a direct impact on the large-scale circulation. In contrast, Wills et al (2016) identified the significant transient atmospheric circulation responses that lag the SST anomalies in the GS extension by several weeks, with the pattern of response characterized by the anomalous low (high) sea level pressure (SLP) over the GS region (south of Iceland).…”

“…This difference might be related to different SST conditions between NCEP-1 (time varying but on a coarse grid) and the CTL (daily climatology but on a finer grid). The fact that the model reproduces the observed wintertime basin-scale intrinsic mode of variability is important, since the observed and modeled quasi-steady circulation response often projects onto the dominant modes of internal atmospheric variability (Peng and Robinson 2001;Deser et al 2004Deser et al , 2007Frankignoul and Sennéchael 2007). Comparison of the EOF1 patterns across the different sensitivity simulations suggests that this pattern is still the dominant mode albeit with minor regional-scale differences (not shown).…”

“…The winter GS position is known to exhibit substantial interannual to decadal variations in association with the North Atlantic Oscillation (NAO) (Taylor and Stephens 1998;Joyce et al 2000;Frankignoul et al 2001). The GS is displaced northward (southward) when the NAO is in the positive (negative) phase, with the NAO leading the GS shift by 12-18 months (Frankignoul et al 2001;Sanchez-Franks et al 2016). The lag is explained by the adjustment time scale of the GS position to the NAOdriven wind stress and wind stress curl (Gangopadhyay et al 1992).…”

“…On the other hand, the low-frequency dynamics involving the high-latitude wave-breaking and wave-blocking events (Strong and Magnusdottir 2008) influence the position of the North Atlantic eddy-driven jet and the NAO (Rivière and Orlanski 2007;Woollings et al 2010b). The basin-scale quasi-steady circulation response to extratropical SST forcing often resembles the leading mode of the internal atmospheric variability (Peng and Robinson 2001;Deser et al 2004;Frankignoul and Sennéchael 2007).…”

Seasonal climate forecasting

“…Other climate signals, such as the North Atlantic Oscillation (NAO, e.g. Lamb and Peppler, 1987;Hurrell et al, 2003), the Pacific-North American (PNA) pattern (Frankignoul and Sennechael, 2007), the Indian Ocean Dipole (IOD, Luo et al, 2008) also provide regional predictive potential on the seasonal time scale. For instance, the NAO, a seesaw in pressure between the Icelandic Low and Azores High first introduced by Walker (1924), is now the focal point for much research on climate at mid-high Northern Hemisphere latitudes, especially in western Europe variations from seasonal to decadal time scales (Hurrell, 1995;Katz, 2002).…”