Impact of Ural Blocking on Winter Warm Arctic–Cold Eurasian Anomalies. Part II: The Link to the North Atlantic Oscillation

Abstract

In Part I of this study, the Ural blocking (UB)-induced amplification role of winter warm Arctic-cold Eurasian (WACE) anomalies has been examined. It was found that the long-lived UB together with the positive North Atlantic Oscillation (NAO 1 ) significantly contributes to the amplification of the WACE pattern. The present study examines how the UB variability affects quasi-biweekly WACE (QB-WACE) anomalies and depends on the NAO 1 and North Atlantic conditions by classifying the UB based on a case study of a cold event that occurred over southern China in January 2008. A composite analysis during 1979-2013 shows that the QB-WACE anomalies associated with the UB that often occur with the NAO 1 are strong and influenced by the North Atlantic jet (NAJ) and zonal wind strengths over Eurasia. For NAO 1 -related UB, the QB-WACE anomaly depends strongly on the location of UB, and the UB anomalies lag the NAO 1 by approximately 4-7 days.The strength of the NAJ determines whether the combined NAO 1 and UB anomalies exhibit a negative East Atlantic/West Russia (EA/WR 2 ) pattern, while the region of weak zonal winds over Eurasia and the zonal extent of the NAJ dominate the location of UB. For southward-, eastward-, and westward-displaced UBs associated with a strong NAJ, the NAO 1 favors the UB with a southward-displaced QB-WACE anomaly through wave train propagation like an EA/WR 2 pattern. Eastward-and southward-displaced UB anomalies induce similarly displaced cold anomalies with intrusion into southern China. However, for a northward-displaced UB, this happens without pronounced EA/WR 2 patterns because of a weak NAJ and is accompanied by a northward-displaced QB-WACE anomaly.

Impact of Ural Blocking on Winter Warm Arctic–Cold Eurasian Anomalies. Part I: Blocking-Induced Amplification

“…This can be explained by the close relation between the NAO and UB (Figs. The cause of this NAO-UB relation is easily explained using the theoretical result of Luo et al (2007) based on a nonlinear multiscale interaction model of NAO events, who noted that the decay of the NAO 1 event can lead to downstream blocking through the energy dispersion of Rossby waves. 8a).…”

“…The time that a large-scale blocking event satisfies the meridional height gradient condition, GHGS 5 [Z(f 0 ) 2 Z(f S )]/(f 0 2 f S ) . For the details of this 2D blocking index and the definition of the IB frequency, refer to the papers of Davini et al (2012) and Luo et al (2015). In this paper, our composite analysis is focused on the winters of 1979-2013, and the maximum amplitude of the blocking anticyclonic anomaly during its life cycle is defined as the zero-lag day (lag 0).…”

Changes in Blocking Characteristics during the First Part of the 21st Century

“…Only a few have examined blocking in the 21st century (e.g. [8], [9]). Many have also examined projections for the future occurrence of blocking [7], [10][11][12][13].…”

“…Others projected that far into the future the number of events may decrease slightly [11]. Others, such as [8] and [9] suggest that the primary location for block ccurrences would also change in a warmer world.…”

Trends of Heat Waves and Cold Spells over 1951–2015 in Guangzhou, China

“…In India, the frequency of cold nights decreased considerably over 1969-2005 and the trends in the number of warm days increased significantly only in the interior peninsula [7,14,15]. In western Eurasia, a rapid increase in regional heat waves was observed since 2010, which was associated with the increasing frequency of large-scale, quasi-stationary positive centers of maximum height anomalies in the upper troposphere and the phase change of the Atlantic Multi-decadal Oscillation (AMO) [9,16,17]. The regional differences in historical trends of extreme temperatures need to take into account projected temperature increases under climate change scenarios and assessment of the impacts of climate change.…”