Maintenance mechanisms of the Scandinavian teleconnection pattern and its possible impact on the Eurasian climate are investigated on the basis of long-term monthly data. Its upstream portion over the North Atlantic is forced and maintained by feedback forcing from transient eddies migrating along the nearby storm track, with an additional contribution from incoming Rossby wave activity from further upstream. The primary anomaly centre over the Scandinavian Peninsula and the downstream portion of the pattern manifest themselves basically as Rossby waves propagating towards central Siberia and east Asia, under the modest feedback forcing from transient eddies. The pattern shows apparent seasonality in its dynamical properties, including the wave-train orientation and wavelength, under the seasonally varying transienteddy feedback forcing and waveguide structure for Rossby waves. In cold seasons, the positive phase of the pattern causes cold-air accumulation over a vast area extending from western Siberia to the regions around Lake Baikal and Lake Balkhash, while giving rise to decreased precipitation over northeastern Europe, western Siberia and some of the Arctic coastal regions. The pattern also changes the North Atlantic sea surface temperature differently between autumn and winter.
A pre-existing anticyclonic anomaly over Scandinavia/western Russia played a crucial role in the persistent low temperature event over southern China in January 2008. This anticyclonic anomaly extended eastward along the arctic coast of the Eurasian continent, and then induced the persistent low temperature over southern China. Considering that anticyclonic anomalies over Scandinavia/western Russia rarely extended eastward to central Siberia, the simultaneous presence of this feature along with the vigorous Rossby wave propagation along the African-Asian jet stream is found to be a fundamental factor in the occurrence of the persistent event.
A deep and cold vortex circulation often occurs over northeast China. Known as the northeast China cold vortex (NCCV), the phenomenon is most active from May to mid-June and can lead to extremely cold local temperatures. This study used rotated principle component analysis to categorize NCCV events into four types, which were characterized by ridges (or blocks) over the following regions: Lake Baikal (BKL), the Yenisei River valley (YNS), the Ural Mountains (UR), and the Yakutsk–Okhotsk region (YO). On the intraseasonal time scale, it was found that BKL- and YNS-type NCCVs formed when the wave train height anomalies originating from the North Atlantic and Europe propagated to East Asia. In contrast, YO- and UR-type NCCVs formed in conjunction with the development of a meridional dipole pattern over northeast Asia. The existence of a blocking-type circulation over the Yakutsk–Okhotsk region favored maintenance of the NCCV circulation for the long-lived (more than 5 days) NCCV events of the four types. The typical circulation over northeast Asia for the long-lived NCCV event was closely associated with wave breaking, whereas the short-lived (3–5 days) event showed only wave propagation. The YNS-type NCCV caused cold surface air temperatures (SAT) not only over northeast China, but also over central and south China, whereas the other three types led only to regional cold SAT anomalies over northeast China. All four types of NCCVs caused a precipitation increase over northeast China, and this effect was broader for the UR- and YO-type NCCVs than that for BKL- and YNS-type NCCVs.
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