Abstract
A remarkable feature of interannual climate variability is a robust link of wintertime anomalies of surface air temperature (SAT) in northern Asia to pan-Atlantic SAT variations associated with the North Atlantic Oscillation (NAO). Here statistical analyses of data from the era of satellite observations (1979–2017) are used to show that about 80% of the variance of the winter (December-March) mean area-averaged SAT anomalies in northern Asia can be explained by the anomalous surface circulation associated with an NAO-like mode of sea level pressure variability over extratropical Eurasia. These SAT anomalies are related equally strongly to the “Lake Baikal” vortex representing variations of the upper-tropospheric circulation over northern Asia. Support is given for the scenario that this vortex drives SAT anomalies in northern Asia via surface-reaching displacements of isentropic surfaces and that it is coupled to climate variability in the Euro-Atlantic sector via interactions between the North Atlantic storm track, quasi-stationary planetary waves, and zonal-mean zonal winds. The results underpin the importance of a lesser-known zonal wavenumber-3 structure of disturbances trapped over Eurasia by the polar front jet rather than the better-known zonal wavenumber-5 structure of disturbances trapped by the subtropical jet for NAO teleconnections.
Highlights
Climatic anomalies are usually defined as departures of primary climate variables, such as the sea level pressure (SLP) or surface air temperature (SAT), averaged over a specific timespan from their climatological means or secular trends
That study showed a strong association between the “Lake Baikal” vortex and the leading empirical orthogonal function (EOF) mode of the wintertime storm track activity (STA) over Eurasia, hereafter referred to as the STAEA mode, that is closely related to the North Atlantic Oscillation (NAO). It showed that the STAEA-related “Lake Baikal” vortex is embedded in a wavenumber-3 circumglobal waveguide pattern (CWP3) guided by the polar front jet. These results suggest that interactions between the North Atlantic storm track and high-latitude stationary waves are instrumental in the linkage of SAT anomalies in northern Asia to the NAO
A remarkable feature of climate variability in the North Atlantic-Eurasian region is a robust NAO-related recurrence of a lobe of coherent wintertime air temperature anomalies extending from the Atlantic to the Pacific coast of northern Eurasia
Summary
A remarkable feature of interannual climate variability is a robust link of wintertime anomalies of surface air temperature (SAT) in northern Asia to pan-Atlantic SAT variations associated with the North Atlantic Oscillation (NAO). The STAEA index correlates highly with the SATA index (r = 0.80; see Table 1) and the SLPEA index (r = 0.88; see Supplementary Fig. S1d for comparison of the time series), as well as the NAO (r = 0.83) and GPHLB (r = 0.76) indices[8] Consistent with these tight relations, the STAEA-covariant anomaly patterns exhibit all major features associated with the other indices, including the upper-tropospheric “Lake Baikal” vortex and large static stability anomalies in the vortex area (see Fig. 6c; arrows for the wind anomalies and thin contours and color shading for the buoyancy frequency anomalies at 300 hPa). V300 hPa (in m s−1). (Z3⁎00, thin (c) Anomalies of the zonally contours and color shading) asymmetric component of the regressed onto the STAEA index
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