scholarly journals Assessment of the Teleconnection Patterns Affecting July Precipitation in China and Their Forcing Mechanisms in the Met Office Unified Model

2020 ◽  
Vol 33 (13) ◽  
pp. 5727-5742 ◽  
Author(s):  
Maria João Carvalho ◽  
Sean F. Milton ◽  
José M. Rodríguez
Keyword(s):  
North Atlantic Ocean ◽  
Meridional Wind ◽  
Teleconnection Pattern ◽  
Silk Road ◽  
Teleconnection Patterns ◽  
Modes Of Variability ◽  
The North ◽  
Silk Road Pattern ◽  
The Impact ◽  
The Silk Road

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.

scholarly journals Interdecadal Variations of the Silk Road Pattern

2017 ◽  
Vol 30 (24) ◽  
pp. 9915-9932 ◽  
Author(s):  
Lin Wang ◽  
Peiqiang Xu ◽  
Wen Chen ◽  
Yong Liu
Keyword(s):  
Wave Train ◽  
Atlantic Multidecadal Oscillation ◽  
Teleconnection Pattern ◽  
Silk Road ◽  
Boreal Summer ◽  
Northeastern Asia ◽  
Western Asia ◽  
Silk Road Pattern ◽  
Decadal Climate ◽  
The Silk Road

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.

Potential Predictability of the Silk Road Pattern and the Role of SST as Inferred from Seasonal Hindcast Experiments of a Coupled Climate Model

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
Keyword(s):  
North Atlantic ◽  
Silk Road ◽  
Potential Predictability ◽  
The North ◽  
Silk Road Pattern ◽  
The North Atlantic ◽  
Upper Level ◽  
The Silk Road ◽  
Wind Bias

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.

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
Keyword(s):  
South Asia ◽  
Time Scales ◽  
Prediction Models ◽  
Decadal Variability ◽  
Causal Effect ◽  
Vertical Motion ◽  
Silk Road ◽  
The North ◽  
Silk Road Pattern ◽  
The Silk Road

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.

scholarly journals Excitation Mechanisms of the Teleconnection Patterns Affecting the July Precipitation in Northwest China

2012 ◽  
Vol 25 (22) ◽  
pp. 7834-7851 ◽  
Author(s):  
Guosen Chen ◽  
Ronghui Huang
Keyword(s):  
Northwest China ◽  
Silk Road ◽  
Central Pacific ◽  
Tropical Rainfall ◽  
Teleconnection Patterns ◽  
Excitation Mechanisms ◽  
Silk Road Pattern ◽  
Rainfall Variations ◽  
The Silk Road ◽  
Tropical Heating

Abstract Using observational rainfall data and atmospheric reanalysis data, the precipitation variations in Northwest China during July and the corresponding atmospheric teleconnection patterns are studied. The results indicate that the leading modes of July precipitation variations in Northwest China are affected by the Silk Road pattern and the Europe–China (EC) pattern. The analysis suggests that the circumglobal teleconnection (CGT) could be considered as the interannual component of the Silk Road pattern. To investigate the excitation mechanisms for the CGT pattern and EC pattern on interannual time scales, the singular value decomposition (SVD) analysis is performed between 200-hPa meridional wind velocity over the region of (30°–60°N, 30°–130°E) and tropical rainfall between (15°S and 30°N). The results suggest that the tropical heating anomalies most responsible for the CGT pattern are located over the North Indian Ocean, and the tropical heating anomalies most responsible for EC pattern are located over equatorial central Pacific, Indonesia, and tropical Atlantic. The tropical heating anomalies excite the CGT pattern and EC pattern by inducing divergent flow at the upper troposphere, and the advections of vorticity by the divergent component of the flow act as effective Rossby wave sources. Further analysis indicates that the tropical rainfall anomalies responsible for the CGT pattern and EC pattern are the leading modes of tropical rainfall variations, and these modes of tropical rainfall variations are related to the SST anomalies.

scholarly journals Differences in the Silk Road Pattern and Its Relationship to the North Atlantic Oscillation between Early and Late Summers

2018 ◽  
Vol 31 (22) ◽  
pp. 9283-9292 ◽  
Author(s):  
Xiaowei Hong ◽  
Riyu Lu ◽  
Shuanglin Li
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Late Summer ◽  
Early Summer ◽  
Silk Road ◽  
The North ◽  
Eurasian Continent ◽  
Silk Road Pattern ◽  
The North Atlantic ◽  
The Silk Road

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.

scholarly journals The North China/Northeastern Asia Severe Summer Drought in 2014

2015 ◽  
Vol 28 (17) ◽  
pp. 6667-6681 ◽  
Author(s):  
Huijun Wang ◽  
Shengping He
Keyword(s):  
North China ◽  
East Asian ◽  
Teleconnection Pattern ◽  
Severe Drought ◽  
European Continent ◽  
The Past ◽  
The North ◽  
Asian Summer ◽  
Silk Road Pattern ◽  
The Silk Road

Abstract In summer 2014, north China and large areas of northeastern Asia (NCNEA) suffered from the most severe drought of the past 60 years. This study indicates that the East Asian summer precipitation in 2014 exhibited a tripole anomaly, with severe negative anomalies in NCNEA, strong positive anomalies in south China, South Korea, and Japan, and intense negative anomalies in the western North Pacific. Along with the severe tripole precipitation anomalies, there were strong intensities of the Silk Road pattern, the Pacific–Japan pattern, and the Eurasian teleconnection pattern, which were responsible for the strong precipitation anomaly in 2014 through changes to the western Pacific subtropical high (WPSH) and the East Asian trough. Further analysis indicates that the sea surface temperature (SST) in the North Pacific was nearly the warmest in the past 60 years and, together with the strong SST warming in the warm pool region, thus caused the strong Pacific–Japan teleconnection pattern, southward positioning of the WPSH, and weakened East Asian summer monsoon. Additionally, the summertime sea ice cover in the Arctic Ocean was anomalous, resulting in high SST in the Laptev–Kara Sea and, hence, triggering a strong Eurasian teleconnection pattern and contributing to the severe drought of NCNEA. Furthermore, the intense warming over the European Continent and Caspian Sea favored the Silk Road pattern, also contributing to the southward positioning of the WPSH and the NCNEA drought. The NCNEA severe drought was therefore the joint result of Pacific SST anomalies, Arctic sea ice anomalies, and warming over the European Continent and Caspian Sea.

scholarly journals North Atlantic Modulation of Interdecadal Variations in Hot Drought Events over Northeastern China

2020 ◽  
Vol 33 (10) ◽  
pp. 4315-4332 ◽  
Author(s):  
Huixin Li ◽  
Shengping He ◽  
Yongqi Gao ◽  
Huopo Chen ◽  
Huijun Wang
Keyword(s):  
High Temperature ◽  
North Atlantic ◽  
Time Scale ◽  
Wave Train ◽  
Silk Road ◽  
Northeastern China ◽  
The North ◽  
Silk Road Pattern ◽  
The North Atlantic ◽  
The Silk Road

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.

Long-term ventilation changes of Subpolar Mode Waters in the North Atlantic Ocean and its impact on the oxygen distribution

2021 ◽  
Author(s):  
Ilaria Stendardo ◽  
Bruno Buongiorno Nardelli ◽  
Sara Durante
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Horizontal Resolution ◽  
Late Winter ◽  
Mode Water ◽  
Mode Waters ◽  
The North ◽  
The North Atlantic ◽  
The Impact

<p>In the subpolar North Atlantic Ocean, Subpolar Mode Waters (SPMWs) are formed during late winter convection following the cyclonic circulation of the subpolar gyre. SPMWs participate in the upper flow of the Atlantic overturning circulation (AMOC) and provide much of the water that is eventually transformed into several components of the North Atlantic deep water (NADW), the cold, deep part of the AMOC. In a warming climate, an increase in upper ocean stratification is expected to lead to a reduced ventilation and a loss of oxygen. Thus, understanding how mode waters are affected by ventilation changes will help us to better understand the variability in the AMOC. In particular, we would like to address how the volume occupied by SPMWs has varied over the last decades due to ventilation changes, and what are the aspects driving the subpolar mode water formation, their interannual variations as well as the impact of the variability in the mixing and subduction and vertical dynamics on ocean deoxygenation. For this purpose, we use two observation-based 3D products from Copernicus Marine Service (CMEMS), the ARMOR3D and the OMEGA3D datasets. The first consists of 3D temperature and salinity fields, from the surface to 1500 m depth, available weekly over a regular grid at 1/4° horizontal resolution from 1993 to present. The second consists of observation-based quasi-geostrophic vertical and horizontal ocean currents with the same temporal and spatial resolution as ARMOR3D.</p>

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