Impact of Northwest Atlantic SST Anomalies on the Circulation over the Ural Mountains during Early Winter

Abstract

Both the observed background circulation and the northwest Atlantic sea surface temperature anomalies (SSTA) associated with the circulation anomaly over the Ural Mountains during early winter (October-December) are investigated, and it is shown that a positive height anomaly over the Urals is remotely linked to a positive SSTA by an upper wave-train-like anomaly chain across the North Atlantic and coastal Europe. To investigate whether and how the SSTA affects the circulation over the Urals, large-ensemble atmospheric general circulation model (GCM) experiments are conducted, and the results show that the SSTA forces a similar wave-train-like anomaly chain, resulting in a positive geopotential height anomaly over the Urals.The mechanism that maintains the response is diagnosed by investigating the roles of anomalous diabatic heating, and transient vorticity forcing, via a linear baroclinic model (LBM). The results suggest that the two upstream anomalies in the chain are largely maintained by anomalous transient vorticity forcing, although it is modulated by anomalous diabatic heating. In contrast, the Ural response is largely maintained by anomalous diabatic heating. To mimic the initial mechanism of the response, an idealized heating representing the initial SSTA-induced heating is prescribed. The LBM response to the idealized heating is obtained, and then transient feedback to the heating-induced anomalous flow is simulated, via a linear storm track model (STM). The LBM responses to the anomalous transient vorticity forcing resulting from the idealized heating resembles the GCM simulation upstream, but is not significant over the Urals. This suggests further that the Ural response is triggered, and maintained, by anomalous diabatic heating.

Effect of the climate shift around mid 1970s on the relationship between wintertime Ural blocking circulation and East Asian climate

“…These signals are consistent with previous studies, and resemble those obtained in early winter (Li, 2004). Takaya and Nakamura (2005) have pointed out that the Ural blocking may cause a synoptic amplification of the SH with the leading period of about 1 week.…”

“…Some studies (e.g. Li, 2004) have focused on this topic in early winter. However, not much attention has been paid to the midwinter situation.…”

Effects of autumn-winter Arctic sea ice on winter Siberian High

“…In fact, autumn SST also displayed a persistent warming trend after 1990 ( Figure 9). The North Atlantic SST anomalies may have a role in forming winter blocking-like anomalies over the Ural Mountains [23], which causes a strengthened winter SH [24]. Additionally, the autumn regional-averaged SWE (40-60N, 60-140E) exhibited an increasing trend after 1990, favoring a strengthening of the SH [25].…”

Decadal variations of the relationship between the summer North Atlantic Oscillation and middle East Asian air temperature

“…This contrast drives the mean surface winds and the midlatitude storms from west to east across the North Atlantic, thus the NAO is the dominant system controlling the climate variability over the North Atlantic and surrounding continents [e.g., van Loon and Rogers, 1978;Wallace and Gutzler, 1981;Barnston and Livezey, 1987;Hurrell, 1995;Hurrell and van Loon, 1997;Li et al, 2003]. Besides the local influence, the NAO has impacts on Asian climate through the teleconnection, consequently resulting in anomalous East Asian winter monsoon [Wu and Huang, 1999;Lu et al, 2007], summer Okhotsk high [Ogi et al, 2004], Asian summer monsoon [Chang et al, 2001;Yang et al, 2004], winter circulation over the Ural Mountains [Li, 2004], and the climate over the east to the Tibetan Plateau in March [Yu and Zhou, 2004].…”