Interdecadal Variability of the Warm Arctic and Cold Eurasia Pattern and Its North Atlantic Origin

Abstract

This study investigates the origin of the interdecadal variability in the warm Arctic and cold Eurasia (WACE) pattern, which is defined as the second empirical orthogonal function of surface air temperature (SAT) variability over the Eurasian continent in Northern Hemisphere winter, by analyzing the Twentieth Century Reanalysis dataset. While previous studies highlight recent enhancement of the WACE pattern, ascribing it to anthropogenic warming, the authors found that the WACE pattern has experienced a seemingly periodic interdecadal variation over the twentieth century. This long-term variation in the Eurasian SAT is attributable to the altered coupling between the Siberian high (SH) and intraseasonal Rossby wave emanating from the North Atlantic, as the local wave branch interacts with the SH and consequentially enhances the continental temperature perturbation. It is further identified that these atmospheric circulation changes in Eurasia are largely controlled by the decadal amplitude modulation of the climatological stationary waves over the North Atlantic region. The altered decadal mean condition of stationary wave components brings changes in local baroclinicity and storm track activity over the North Atlantic, which jointly change the intraseasonal Rossby wave generation and propagation characteristics as well. With simple stationary wave model experiments, the authors confirm how the altered mean flow condition in the North Atlantic acts as a source for the growth of the Rossby wave that leads to the change in the downstream WACE pattern.

Two Leading Modes of Wintertime Atmospheric Circulation Drive the Recent Warm Arctic–Cold Eurasia Temperature Pattern

“…The strong association between the NAO/AO and the first circulation mode discussed in the present study suggests that its recent trend could also be relatively independent of anthropogenic forcing. Regarding the second circulation mode, similar mid-high-latitude wavelike structures can be found in Sato et al (2014) and Sung et al (2018). The driving mechanisms of such patterns are warming SSTs in the Gulf Stream region in the former study and changes in mean-flow condition in the North Atlantic in the latter [see also discussion in section 5c(2)].…”

“…Wave trains emanating from the North Atlantic can interact with surface highs over Eurasia, modulating their strength and location through a complex interplay (cf. Takaya and Nakamura 2005;Sung et al 2018). In our composites, the wave propagation is concomitant to the intensification of a broad high-pressure region spanning northern Eurasia and a strengthening of the water vapor transport toward BKS and the surrounding areas, leading to stronger DLW (Figs.…”

“…Others have analyzed the low-frequency variability in the WACE pattern. Sung et al (2018), for example, have highlighted the existence of a strong interdecadal variability, associated with the modulation of Rossby waves by the mean-flow conditions in the North Atlantic sector, altered atmospheric baroclinicity over the Gulf Stream region, and changes in the Atlantic meridional overturning circulation.…”

Revisiting the trend in the occurrences of the “warm Arctic–cold Eurasian continent” temperature pattern

“…The direction of wave activity flux indicates the direction of group speed of stationary planetary wave. Here, we calculate the wave activity flux defined by Takaya and Nakamura (2001), which considers the influence of midlatitude zonal wind (Fig. 12).…”

“…No significant correlations, however, are found between the filtered time se- Figure 12. The anomalous wave activity flux (vectors) (Takaya and Nakamura, 2001) and stream function (colors, units: 10 7 m 2 s −1 ) from ERA-Interim reanalysis over the 1979-2019 period regressed onto the normalized time series of occurrence number for nodes 1, 4, 6, and 9. Figure 13.…”