scholarly journals A Mechanism for the Recently Increased Interdecadal Variability of the Silk Road Pattern

2019 ◽  
Vol 32 (3) ◽  
pp. 717-736 ◽  
Author(s):  
Claudia Christine Stephan ◽  
Nicholas P. Klingaman ◽  
Andrew G. Turner

The Silk Road pattern (SRP) teleconnection manifests in summer over Eurasia, where it is associated with substantial temperature and precipitation anomalies. The SRP varies on interannual and decadal scales; reanalyses show an increase in its decadal variability around the mid-1970s. Understanding what drives this decadal variability is particularly important, because contemporary seasonal prediction models struggle to predict the phase of the SRP. Based on analysis of observations and multiple targeted numerical experiments, this study proposes a mechanism for decadal SRP variability. Causal effect network analysis confirms a positive feedback loop between the eastern portion of the SRP pattern and vertical motion over India on synoptic time scales. Anomalies over a larger region of subtropical South Asia can reinforce a background state that projects onto the positive or negative SRP through this mechanism. This effect is isolated and confirmed in targeted numerical simulations. The transition from weak to strong decadal variability in the mid-1970s is consistent with more spatially coherent interannual precipitation variability over subtropical South Asia. Furthermore, results suggest that oceanic variability does not directly force the SRP. Nevertheless, sea surface temperatures in the North Atlantic and the North Pacific may indirectly affect the SRP by modulating South Asian rainfall on decadal time scales.

2020 ◽  
Vol 33 (22) ◽  
pp. 9567-9580
Author(s):  
Ronald Kwan Kit Li ◽  
Chi Yung Tam ◽  
Ngar Cheung Lau ◽  
Soo Jin Sohn ◽  
Joong Bae Ahn

AbstractThe Silk Road pattern (SR) is a leading mode of atmospheric circulation over midlatitude Eurasia in boreal summer. Its temporal phase is known to be unpredictable in many models. Previous studies have not reached a clear consensus on the role of sea surface temperature (SST) associated with SR. By comparing seasonal hindcasts from the Pusan National University (PNU) coupled general circulation model with reanalysis, we investigate if there are any sources of predictability originating from the SST. It was found that the PNU model cannot predict SR temporally. In fact, SR is associated with El Niño–Southern Oscillation (ENSO) in the model hindcasts, in contrast to reanalysis results in which SR is more associated with North Atlantic SST anomalies. The PNU system, however, shows potential predictability in SR associated with tropical Pacific SST. Bias in stationary Rossby waveguides is proposed as an explanation for the SR–ENSO relationship in hindcast runs. Model upper-level wind bias in the North Atlantic results in a less continuous waveguide connecting the North Atlantic to Asia, and may hinder wave propagations induced by North Atlantic SST to trigger SR. On the other hand, model upper-level wind bias in the subtropical western Pacific may favor westward propagation of zonally elongated waves from the ENSO region to trigger SR. This study implies that the role of SST with regard to SR can be substantially changed depending on the fidelity of model upper-level background winds.


2021 ◽  
Vol 7 (24) ◽  
pp. eabf9395
Author(s):  
Shuai Hu ◽  
Tianjun Zhou

Skillful near-term climate predictions of rainfall over the Tibetan Plateau (TP), the Asian water tower, benefit billions of people. On the basis of the state-of-the-art decadal prediction models, we showed evidence that although the raw model outputs show low predicted ability for the summer Inner TP (ITP) rainfall due to low signal-to-noise ratios in models, we can produce realistic predictions by extracting the predictable signal from large ensemble predictions along with a postprocessing procedure of variance adjustment. The results indicate that the summer ITP rainfall is highly predictable on multiyear time scales. The predictability of ITP rainfall originates from the Silk Road pattern driven by sea surface temperature over the subpolar gyre region in North Atlantic. Real-time forecasts suggest that the ITP will become wetter, with 12.8% increase in rainfall during 2020–2027 relative to 1986–2005. Our results will help the water resources management in the surrounding regions.


2018 ◽  
Vol 31 (22) ◽  
pp. 9283-9292 ◽  
Author(s):  
Xiaowei Hong ◽  
Riyu Lu ◽  
Shuanglin Li

Abstract The Silk Road Pattern (SRP) is an upper-tropospheric teleconnection pattern along the Asian westerly jet in summer on the interannual time scale, and it exerts great influences on the climate of the Eurasian continent. Results in the present study indicate that the SRP exhibits considerable distinctions between early and late summers (i.e., 1 June–9 July and 10 July–31 August, respectively). The SRP is stronger and more geographically fixed in late summer in comparison with its counterpart in early summer. Furthermore, the SRP is closely connected with the summer North Atlantic Oscillation (SNAO) in late summer, but not in early summer. This closer connection in late summer is manifested clearly in the leading mode of upper-tropospheric meridional wind anomalies over the North Atlantic–Eurasian continent domain. The intensified SNAO–SRP relationship in late summer can be explained by the subseasonal change of the SNAO: albeit being a seesaw pattern common in both early and late summers, there is a shift of this pattern toward the northwest–southeast one in late summer from a north–south one in early summer. The southeastern pole of SNAO in late summer extends into the Eurasian continent, and efficiently triggers the SRP to propagate along the Asian jet. By contrast, the south pole of SNAO in early summer is confined over the North Atlantic and is thus less effective to trigger the SRP propagation.


2020 ◽  
Vol 33 (13) ◽  
pp. 5727-5742 ◽  
Author(s):  
Maria João Carvalho ◽  
Sean F. Milton ◽  
José M. Rodríguez

AbstractIn this study, we evaluate the ability of the MetUM to reproduce the Silk Road (SR) and Europe–China (EC) teleconnection patterns and their relationship with precipitation over China. The SR and EC patterns are the main modes of interannual variability of July upper-tropospheric meridional wind. The three main factors to the formation of these patterns are analyzed: 1) the tropical precipitation anomalies, which act as a forcing mechanism; 2) the emission of Rossby waves in the Mediterranean–Caspian Sea region; and 3) the basic state of the tropospheric jet over Eurasia. It was found that the model has some difficulty reproducing the main modes of variability in atmosphere-only mode (SR and EC pattern correlation of 0.31 and 0.54, respectively) with some improvement in coupled mode (pattern correlations of 0.56 and 0.44, respectively). Relaxation experiments were used to assess the impact that improving circulation in key regions has on the teleconnections. It was found that nudging wind and temperatures in the forcing regions within the tropics improved the Silk Road pattern whereas nudging in the region where the jet transitions between the North Atlantic Ocean and Eurasian continent—correcting the basic state—had the most impact on the EC teleconnection pattern. This suggests that while the Silk Road pattern is more sensitive to changes in the forcing, the Europe–China pattern is more sensitive to the basic state.


2020 ◽  
Vol 33 (10) ◽  
pp. 4315-4332 ◽  
Author(s):  
Huixin Li ◽  
Shengping He ◽  
Yongqi Gao ◽  
Huopo Chen ◽  
Huijun Wang

AbstractBased on the long-term reanalysis datasets and the multivariate copula method, this study reveals that the frequency of summer hot drought events (SHDEs) over northeastern China (NEC) shows interdecadal variations during 1925–2010. It is revealed that the summer sea surface temperature (SST) over the North Atlantic has a significant positive correlation with the frequency of SHDEs over NEC on the decadal time scale, indicating a potential influence of the Atlantic multidecadal oscillation (AMO). Further analyses indicate that during the positive phases of the AMO, the warming SST over the North Atlantic can trigger a stationary Rossby wave originating from the North Atlantic, which splits into two wave trains propagating along two different routes. One is a zonally orientated wave train that resembles the Silk Road pattern, whereas the other is an arching wave train that resembles the polar–Eurasian pattern. A negative (positive) phase of the Silk Road pattern (polar–Eurasian pattern) may result in the weakened westerly wind along the jet stream, the downward vertical motion, and the anomalous positive geopotential center over NEC, providing favorable conditions for precipitation deficiency and high temperature and resulting in increased SHDEs. Thus, the Silk Road pattern and the polar–Eurasian pattern serve as linkages between the AMO and SHDEs over northeastern China in summer on the interdecadal time scale. Model simulations from CAM4 perturbed with warmer SST in the North Atlantic show precipitation deficiency and high temperature conditions over northeastern China in summer, supporting the potential impacts of the North Atlantic SST on SHDEs over northeastern China. The results suggest that the phase of the AMO should be taken into account in the decadal prediction of SHDEs over northeastern China in summer.


2017 ◽  
Vol 30 (24) ◽  
pp. 9915-9932 ◽  
Author(s):  
Lin Wang ◽  
Peiqiang Xu ◽  
Wen Chen ◽  
Yong Liu

Based on several reanalysis and observational datasets, this study suggests that the Silk Road pattern (SRP), a major teleconnection pattern stretching across Eurasia in the boreal summer, shows clear interdecadal variations that explain approximately 50% of its total variance. The interdecadal SRP features a strong barotropic wave train along the Asian subtropical jet, resembling its interannual counterpart. Additionally, it features a second weak wave train over the northern part of Eurasia, leading to larger meridional scale than its interannual counterpart. The interdecadal SRP contributes approximately 40% of the summer surface air temperature’s variance with little uncertainty and 10%–20% of the summer precipitation’s variance with greater uncertainty over large domains of Eurasia. The interdecadal SRP shows two regime shifts in 1972 and 1997. The latter shift explains over 40% of the observed rainfall reduction over northeastern Asia and over 40% of the observed warming over eastern Europe, western Asia, and northeastern Asia, highlighting its importance to the recent decadal climate variations over Eurasia. The Atlantic multidecadal oscillation (AMO) does not show a significant linear relationship with the interdecadal SRP. However, the Monte Carlo bootstrapping resampling analysis suggests that the positive (negative) phases of the spring and summer AMO significantly facilitate the occurrence of negative (positive) phases of the interdecadal SRP, implying plausible prediction potentials for the interdecadal variations of the SRP. The reported results are insensitive to the long-term trends in datasets and thereby have little relevance to externally forced climate change.


2018 ◽  
Vol 31 (3) ◽  
pp. 997-1014 ◽  
Author(s):  
Daniela I. V. Domeisen ◽  
Gualtiero Badin ◽  
Inga M. Koszalka

ABSTRACT The North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) describe the dominant part of the variability in the Northern Hemisphere extratropical troposphere. Because of the strong connection of these patterns with surface climate, recent years have shown an increased interest and an increasing skill in forecasting them. However, it is unclear what the intrinsic limits of short-term predictability for the NAO and AO patterns are. This study compares the variability and predictability of both patterns, using a range of data and index computation methods for the daily NAO and AO indices. Small deviations from Gaussianity are found along with characteristic decorrelation time scales of around one week. In the analysis of the Lyapunov spectrum it is found that predictability is not significantly different between the AO and NAO or between reanalysis products. Differences exist, however, between the indices based on EOF analysis, which exhibit predictability time scales around 12–16 days, and the station-based indices, exhibiting a longer predictability of 18–20 days. Both of these time scales indicate predictability beyond that currently obtained in ensemble prediction models for short-term predictability. Additional longer-term predictability for these patterns may be gained through local feedbacks and remote forcing mechanisms for particular atmospheric conditions.


Author(s):  
Xiaojun Chai

This paper seeks to analyze the ways in which the exchange of silk for horses impacted trade regulations along the Silk Road, thus leading to a rupture in Chinese economic policy. Exchanges between the Qing Dynasty and the Kazakh Khanate were carried between 1759 and 1796, having begun after the Qianlong Emperor vanquished the Dzungar Khanate, which determined the khan of the Kazakhs to swear allegiance to the Emperor. As the Qing Dynasty had up until that point been both politically and economically isolationist, this marked a radical change in its foreign policy.The relation established between emperor and khan is known as chao gong mao yi(朝贡贸易)and is usually translated as vassalage, owing to the similarities with the European concepts, but it also involves the offering of tributes. Traditionally, when discussing the Qianlong Emperor’s decision to consolidate trade with its new vasal, scholars have tended to favor one of three narratives: the first sees this exchange in the same light as the economic relations between the imperial capital and any of China’s provinces, and therefore focuses on the inclusions character of the policy. The second considers the exchange of horses for silk as representing the immediate, dire needs of the two political leaders; while the Khan and his court required fine materials for their own prestige, the Emperor’s armies had an urgent need for horses in the fight against the rebellious Uighurs in Altishahr. The third postulates that engaging in trade would have allowed the isolated Qing to secure their borders.Rather than fully accepting or discarding any of these narratives, a more nuanced position can be gained. We can do this by understanding the implications of vassalage and tribute in close connection with the way in which the whole regional economic policy was modeled around it. I will look at the ways in which chao gong mao yi and its economical meaning were defined in Chinese archives. This will allow us to better understand their interconnected evolution. The Chinese archives that I will look at are formed of two types of documents: the first of these, the jun ji chu lu fu zou zhe (军机处录副奏折), are extensive reports on the affairs of the army, including their military actions and tactics, the power struggles between officers, and the rations needed to feed and supply the troops, to name only a few; the second, the Qianlong chao shi lu (乾隆朝实录), are concise reports that describe in minute detail the affairs of the imperial court. When taken together, these materials paint a vivid picture of the social, economic, and political life of late eighteenth-century China. From these sources we can see that the Qing opted for a sort of tribute trade which made a compromise on the tariff. This shows that while the Qing were clearly making some profit, the need of supplying the armies with horses in Alishahr wasmore important, and they were therefore forced to maintain their conservative economic policy.These materials offer new information which scholars that have tried to defend one of the three narratives in particular have so far neglected. Most important amongst these are two interconnected aspects: on one hand, by investigating how the Silk Road was rebuilt, we see that two different projects were used for the north and for the south. This led to the displacement of the economy towards the north, as it connected several important cities and trade hubs, such as Suzhou、Suzhou . By ignoring the regional impact, historians have tended to downgrade or neglect the changes that this disruption brought to the course of trade. On the other hand, this very separation is the thing that destabilized the region. It caused local unrest, uprisings and separatist tendencies. These episodes of local unrest forced a rethinking of the entire imperial economic policy.The Qianlong Emperor’s policy was never expansionist, neither in territorial nor in economic terms. While they were clearly aware of the importance of forging a strong relationship with their northern Kazakh neighbors, they never had any ambitions to expand towards inner Asia. We can observe this in the way in which the economic policy that they initiated with the Khanate later form the basis for the trade routes with Russia through Qiaketu. These routes would economically drain the Kazahks in the long term. That China was not expansionist at this point can easily be observed from the fact that it hesitated to break out of its traditional approach even when the Kazakhs were weakened, so it was the Russian who eventually absorbed them.To conclude, it can be said that a new understanding of China’s attitudes as a regional actor during the period of Qing Dynasty can be gained by looking at smaller units and understanding how different types of regional or local economic policies evolved together. Quite often, these impacted not only interconnected regions but the empire as a whole. As we have seen, the exchange of silk for horses along the Silk Road is just one such example. Given the rich material that is available in the Chinese archives, many other aspects could be studied.


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