Ural Blocking Research Articles

Implications of Ural Blocking for East Asian Winter Climate in CMIP5 GCMs. Part I: Biases in the Historical Scenario

Abstract This study assesses the ability of the 25 GCMs from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to simulate Ural blocking (UB) and its linkage with the East Asian winter climate [December–February (DJF)] in a historical run (1950/51–2004/05). A Ural blocking index (UBI) is defined as the DJF-mean blocking frequency over 45°–90°E for each winter. Regression analyses suggest that the long-term mean bias of UBI is caused by the long-term mean circulation bias over the North Atlantic. On seasonal time scales, the GCMs simulating a positive bias of UBI are associated with a stronger Atlantic jet stream, as well as stronger westerly momentum fluxes from the North Atlantic to Europe. On synoptic time scales, however, these GCMs tend to be associated with a weaker Siberian high and East Asian trough during the evolution of a UB event. Altogether, there is no apparent linkage between the long-term mean bias of UB and the East Asian winter climate. Further studies are needed to explore the teleconnection between UB and the East Asian winter climate in the GCMs.

Implications of Ural Blocking for East Asian Winter Climate in CMIP5 GCMs. Part II: Projection and Uncertainty in Future Climate Conditions

Abstract Multiple model ensembles (MMEs) of Ural blocking frequency in 20 CMIP5 GCMs show no apparent increase or decrease in RCP4.5 and 8.5 runs throughout the twenty-first century. However, a significant increasing or decreasing trend of the Ural blocking index (UBI) is identified in individual GCMs, and the trend appears to be correlated with the trend of the Siberian high index (SHI), which measures the East Asian winter climate. Regression analyses reveal that the trend of UBI is related to upstream circulation over the Euro-Atlantic region, such as the intensification of the Atlantic jet stream and the propagation of a quasi-stationary Rossby wave across Eurasia. In the late twenty-first century, the year-to-year variation of UBI appears to show a stronger linkage with the large-scale circulation over the Kara and Laptev Seas. Meanwhile, UB likely exerts a stronger impact on East Asia on synoptic and seasonal time scales. The uncertainty of UB might present a challenge for accurate prediction of the subseasonal and long-term variation of the East Asian winter climate. To further evaluate the uncertainty in projections of UB, additional work should assess the atmospheric response to the sea surface temperature over the Atlantic and the reduction of sea ice.

북극 온난화에 따른 겨울철 대기 변동성 분석 연구

The "Barents Oscillation (BO)", first designated by Paul Skeie (2000), is an anomalous recurring atmospheric circulation pattern of high relevance for the climate of the Nordic Seas and Siberia, which is defined as the second Emperical Orthogonal Function (EOF) of monthly winter sea level pressure (SLP) anomalies, where the leading EOF is the Arctic Oscillation (AO). BO, however, did not attracted much interest. In recent two decades, variability of BO tends to increase. In this study, we analyzed the spatio-temporal structures of Atmospheric internal modes such as Arctic Oscillation (AO) and Barents Oscillation (BO) and examined how these are related with Arctic warming in recent decade. We identified various aspects of BO, not dealt in Skeie (2000), such as upper-level circulation and surface characteristics for extended period including recent decade and examined link with other surface variables such as sea-ice and sea surface temperature. From the results, it was shown that the BO showed more regionally confined spatial pattern compared to AO and has intensified during recent decade. The regional dipolelar structure centered at Barents sea and Siberia was revealed in both sea-level pressure and 500 hPa geopotential height. Also, BO showed a stronger link (correlation) with sea-ice and sea surface temperature especially over Barents-Kara seas suggesting it is playing an important role for recent Arctic amplification. BO also showed high correlation with Ural Blocking Index (UBI), which measures seasonal activity of Ural blocking. Since Ural blocking is known as a major component of Eurasian winter monsoon and can be linked to extreme weathers, we suggest deeper understanding of BO can provide a missing link between recent Arctic amplification and increase in extreme weathers in midlatitude in recent decades.

Simulation and Projection of Northern Hemisphere Blockings In CMIP5 Models

The frequencies of atmospheric blocking are analyzed as simulated in 16 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) over North Hemisphere especially over key regions where blocking highs influencing China (the Ural, Baikal and Okhotsk), and the Representative Concentration Pathway 4.5 (RCP4.5) integrations are used to examine projected future changes in a warmer climate. Comparison with reanalysis data reveals that the frequencies of North Atlantic-Eurasia blocking are significantly underestimated throughout the year, however, multi-model mean generally overestimates the blocking frequency over high-latitude of Pacific. Ural blocking, Lake Baikal and Okhotsk Sea blocking frequencies are found to be mainly underestimated especially during the cold season. The RCP4.5 integrations show a heavily reduced for blocking frequency over North Atlantic and higher latitude of Eurasia in 2044-2099, but high-latitude blocking over Atlantic and Pacific presents a small increase. A significant increase of the Ural blocking is found. In contrast to the trend of blocking index for RCP4.5 path in the second half of the 21st, the increasing trend from 2006 to 2050 is distinct, the blocking increasing trend is more significant in summer than in winter over the three regions.

Boreal summer convection oscillation over the Indo‐Western Pacific and its relationship with the East Asian summer monsoon

AbstractStatistical analysis shows that the Indo‐Pacific convection oscillation (IPCO) in boreal summer undergoes quasi‐biennial variability, and is closely related to the East Asian summer monsoon (EASM). Negative IPCO phases, which exhibit an enhanced convection over the north Indian Ocean and a suppressed convection over the western North Pacific, favor a weakened EASM and an increase of summer rainfall in the Yangtze River valley with the joint actions of the stronger than normal Ural and Okhotsk blocking highs and the subtropical western Pacific high, and vice versa. Copyright © 2013 Royal Meteorological Society

Interannual variations of the blocking high over the Ural Mountains and its association with the AO/NAO in boreal winter

This paper analyzes interannual variations of the blocking high over the Ural Mountains in the boreal winter and their association with the Arctic Oscillation/North Atlantic Oscillation (AO/NAO). In January, the relationship between the Ural blocking high (UR) and the AO index is statistically significant. The UR tends to occur more frequently and with greater strength during negative AO periods. Some strong URs also occur during positive AO phases (positive UR-AO events), as in January 2008. This paper discusses the characteristics of atmospheric circulation in the cases of positive UR-AO events and contrast cases (negative UR-AO events). The eastward extending of the Icelandic Low (IL) center and the associated NAO dipole anomaly pattern in the upstream region may play a more important role for the UR-AO events. When the center of the IL shifts eastward to 30°W, the amplitude of zonal wavenumber 2 (wavenumber 3) is intensified in the positive (negative) UR-AO events, which favors positive (negative) height anomalies over the Urals. Further analyses indicate that the intensified zonal wind in high latitudes and weakened zonal wind in midlatitudes over the North Atlantic Ocean render the eastward shift of the IL and the NAO dipole anomaly pattern. The Ural blocking in January 2008 bears similar characteristics to the positive UR-AO events.

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

AbstractBlocking variability over the Ural Mountain region in the boreal winter and its relationship with the East Asian winter climate is investigated. The climate shift around mid 1970s has been shown to exert a significant influence on the blocking pattern. In contrast with the years before 1976/1977, the Ural blocking signal after 1976/1977 is found to propagate less into the stratosphere and more eastward in the troposphere to East Asia, which therefore exerts more influence on the East Asian winter climate. This enhanced Ural blocking–East Asian climate relationship amplifies the impact of Ural blocking on East Asia and, with the background of decreasing Ural blocking, contributes to the higher frequency of warm winters in this region. Further analyses suggest that the NAM‐related stratospheric polar vortex strength and its modulation on the propagation of atmospheric stationary waves can account for this change, with the key area being located in the North Atlantic region. Copyright © 2009 Royal Meteorological Society

Adjoint sensitivity analyses on the anomalous circulation features in East Asian summer monsoon

The concept of optimal sensitivity perturbation (OSP) is developed based on adjoint sensitivity analysis theory. The persistent anomalous features in East Asian summer monsoon system, including the Ural blocking, the Okhotsk Sea dipole blocking and the variations of subtropical high are analyzed and the OSP for each of them evaluated. The results provide us with some new insight into the most significant influential factors for these features. It also demonstrates the great potential for further applications of this method in diagnostics of atmospheric processes.