An Interdecadal Change of the Boreal Summer Silk Road Pattern around the Late 1990s

2020 ◽  
Vol 33 (16) ◽  
pp. 7083-7100
Author(s):  
Yong Liu ◽  
Wen Zhou ◽  
Xia Qu ◽  
Renguang Wu
Keyword(s):  
Climate Impact ◽  
Teleconnection Pattern ◽  
Silk Road ◽  
Boreal Summer ◽  
Interdecadal Change ◽  
Westerly Jet ◽  
Leading Mode ◽  
Precipitation Anomalies ◽  
Silk Road Pattern ◽  
Upper Level

AbstractThe Silk Road pattern (SRP) is a well-known teleconnection pattern along the upper-level westerly jet over the Eurasian continent during boreal summer. The SRP has experienced an interdecadal change around the late 1970s. The present study identified a new change of the SRP around the late 1990s, which is characterized by significant weakening and zonal phase shift of the major centers of the SRP during the recent decades. The recent reshaping of the SRP is attributed to an enhanced impact of precipitation anomalies over the northeastern Indian summer monsoon (ISM), which is associated with the leading mode change of the ISM precipitation anomalies around the late 1990s. The interdecadal weakening of the upper-level westerly jet over central and East Asia also favors the southward movement of the SRP during recent periods. The differences of the features, climate impact, and causes related to the recent SRP change from those related to the SRP change around the late 1970s are also contrasted in this study.

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.

scholarly journals The Meridional Displacement of the Summer Asian Jet, Silk Road Pattern, and Tropical SST Anomalies

2016 ◽  
Vol 29 (10) ◽  
pp. 3753-3766 ◽  
Author(s):  
Xiaowei Hong ◽  
Riyu Lu
Keyword(s):  
Significant Relationship ◽  
Statistical Significance ◽  
Silk Road ◽  
Tropospheric Temperature ◽  
Temperature Anomalies ◽  
Western Asia ◽  
Meridional Displacement ◽  
Leading Mode ◽  
Silk Road Pattern ◽  
Sst Anomalies

Abstract The Silk Road pattern (SRP), which depicts the teleconnection pattern along the Asian jet, has been extensively investigated and commonly described as the leading mode of upper-tropospheric meridional wind anomalies in summer. In this study, the SRP is identified as having a significant relationship with the meridional displacement of the Asian jet (JMD), which manifests as the leading mode of upper-tropospheric zonal wind anomalies. This significant relationship is confirmed by the correlation coefficient between the indices for JMD and SRP, which is 0.39 and reaches statistical significance at the 0.01 level. When the Asian jet is in a northward (southward) displacement, the phase of SRP tends to be shown as anticyclonic (cyclonic) anomalies over western Asia and East Asia and cyclonic (anticyclonic) anomalies over Europe and central Asia. The authors propose an internal atmospheric mechanism for this relationship. In addition, it is found that the JMD is significantly affected by the tropical surface temperature anomalies. In particular, the negative (positive) SST anomalies in the tropical central and eastern Pacific of the preceding spring lead to significant cooler (warmer) tropical tropospheric temperatures in summer and may induce the northward (southward) displacement of the Asian jet through modifying the meridional gradient of tropospheric temperatures. The tropical tropospheric temperature anomalies may also affect the SRP through the JMD.

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.

Interdecadal Variations in the Frequency of Persistent Hot Events in Boreal Summer over Midlatitude Eurasia

2019 ◽  
Vol 32 (16) ◽  
pp. 5161-5177 ◽  
Author(s):  
Ning Shi ◽  
Yicheng Wang ◽  
Xiaoqiong Wang ◽  
Pinyu Tian
Keyword(s):  
Time Scale ◽  
Wave Train ◽  
Northern China ◽  
Stationary Wave ◽  
Silk Road ◽  
Boreal Summer ◽  
Western Asia ◽  
Silk Road Pattern ◽  
The Silk Road ◽  
Circulation Changes

ABSTRACT Based on the daily Japanese 55-year Reanalysis (JRA-55) dataset, this study reveals that southern Europe/western Asia (SEWA) and northern China are two large-scale regions that have exhibited consistent interdecadal variations in the frequency of persistent hot events (PHEs). Over the past 58 summers, the period approximately from 1973 to 1996 represents an inactive period for the occurrence of PHEs over the two regions, whereas the antecedent and subsequent periods are active periods. At the subseasonal time scale, the regional PHEs over SEWA are characterized by quasi-stationary wave train anomalies aloft from the northwest Atlantic to Europe, while the regional PHEs over northern China are characterized by quasi-stationary wave train anomalies over the Eurasian continent. The persistence of the quasi-stationary anomalies is associated with the Rossby wave propagation. Moreover, the energy extraction from the basic flow is also favorable for their persistence. Our study reveals that the above typical circulation anomalies for the PHEs over both SEWA and northern China are in phase with the background circulation changes during the two active periods. Thus, the interdecadal changes in background circulation can modulate the frequency of PHEs over the two regions simultaneously. Further analysis reveals that the background circulation changes are closely related to the interdecadal variation in the Silk Road pattern based on their similarities in both spatial pattern and temporal variation. The sea surface temperature over four particular regions seems to facilitate the phase shifts in the Silk Road pattern on the interdecadal time scale.

scholarly journals Weakened Connection between East China Summer Rainfall and the East Asia-Pacific Teleconnection Pattern

Atmosphere ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 704
Author(s):  
Xiaoxue Yin ◽  
Lian-Tong Zhou ◽  
Jingliang Huangfu
Keyword(s):  
East Asia ◽  
Vertical Motion ◽  
Summer Rainfall ◽  
Teleconnection Pattern ◽  
Asia Pacific ◽  
East China ◽  
Boreal Summer ◽  
Interdecadal Change ◽  
Rainfall Anomalies ◽  
Action Center

The interdecadal change in the relationship between the East Asia-Pacific (EAP) teleconnection pattern and rainfall over East China during boreal summer (June–August) was investigated using observation and reanalysis datasets during 1951–2018. As proposed in a previous study, summer rainfall in the Yangtze-Huaihe River (YH-R) valley is below (above) normal when a positive (negative) EAP event occurs. Based on the close relationship with the rainfall anomalies, the EAP teleconnection pattern has been widely used in the prediction of summer rainfall variations in the YH-R valley. However, we found that the rainfall anomalies in the YH-R basin associated with the EAP pattern were weaker and less evident after the late 1980s. This finding indicates a decreased relationship between the EAP pattern and YH-R basin summer rainfall after the late 1980s, and a decrease in the quality and skill of seasonal predictions of YH-R basin summer rainfall related to the EAP pattern. This pronounced weakening in the YH-R summer rainfall-EAP pattern connection is attributed to the northeastward displacement of the Japanese action center of the EAP pattern after the late 1980s, which caused weaker anomalous vertical motion and moisture transportation over the YH-R valley. The present research reveals that the interdecadal expansion in the size of the Indo-Pacific warm pool in the late 1980s is likely responsible for the northeastward shift in the Japanese action center of the EAP teleconnection pattern by modulating anomalous convective activities and the northward propagation of the EAP pattern.

scholarly journals The driving processes of concurrent hot and dry extreme events in China

2021 ◽  
Author(s):  
Fangxing Tian ◽  
Nicholas Klingaman ◽  
Buwen Dong
Keyword(s):  
Extreme Events ◽  
Southern China ◽  
Eastern China ◽  
Intraseasonal Oscillation ◽  
Silk Road ◽  
Height Anomaly ◽  
Boreal Summer ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Silk Road Pattern ◽  
The Silk Road

<p>Sub-seasonal heatwave-driven concurrent hot and dry extreme events (HDEs) can cause substantial damage to crops, and hence to lives and livelihoods. However, the physical processes that lead to these devastating events are not well-understood.</p><p>Based on observations and reanalysis data for 1979-2016 over China, we show that HDEs occur preferentially over central and eastern China (CEC) and southern China (SC), with a maximum of 3 events year<sup>-1</sup> along the Yangtze Valley. The probability of longer-lived and potentially more damaging HDEs is larger in SC than in CEC. Over SC the key factors of HDEs—positive anomalies of surface air temperature and evapotranspiration, and negative anomalies of soil moisture—begin two pentads before maximising at the peak of the HDEs. These anomalies occur south of a positive height anomaly at 200 hPa, associated with a large-scale subsidence anomaly. The processes over CEC are similar to SC, but the anomalies begin one pentad before the peak. HDE frequency is strongly related to the Silk Road Pattern and the Boreal Summer Intraseasonal Oscillation. Positive phases of the Silk Road Pattern and suppressed phases of the Boreal Summer Intraseasonal Oscillation are associated with positive height anomalies over CEC and SC, increasing HDE frequency by about 35-54% relative to the climatological mean.  Understanding the effects of sub-seasonal and seasonal atmospheric circulation variability, such as the Silk Road Pattern and Boreal Summer Intraseasonal Oscillation, on HDEs is important to improve HDE predictions over China.</p>

scholarly journals The driving processes of concurrent hot and dry extreme events in China

2020 ◽  
pp. 1-40
Author(s):  
Fangxing Tian ◽  
Nicholas P. Klingaman ◽  
Buwen Dong
Keyword(s):  
Extreme Events ◽  
Southern China ◽  
Eastern China ◽  
Intraseasonal Oscillation ◽  
Silk Road ◽  
Height Anomaly ◽  
Boreal Summer ◽  
Boreal Summer Intraseasonal Oscillation ◽  
Silk Road Pattern ◽  
The Silk Road

AbstractSub-seasonal heatwave-driven concurrent hot and dry extreme events (HDEs) can cause substantial damage to crops, and hence to lives and livelihoods. However, the physical processes that lead to these devastating events are not well-understood. Based on observations and reanalysis data for 1979-2016 over China, we show that HDEs occur preferentially over central and eastern China (CEC) and southern China (SC), with a maximum of 3 events year-1 along the Yangtze Valley. The probability of longer-lived and potentially more damaging HDEs is larger in SC than in CEC. Over SC the key factors of HDEs—positive anomalies of surface air temperature and evapotranspiration, and negative anomalies of soil moisture—begin two pentads before maximising at the peak of the HDEs. These anomalies occur south of a positive height anomaly at 200 hPa, associated with a large-scale subsidence anomaly. The processes over CEC are similar to SC, but the anomalies begin one pentad before the peak. HDE frequency is strongly related to the Silk Road Pattern and the Boreal Summer Intraseasonal Oscillation. Positive phases of the Silk Road Pattern and suppressed phases of the Boreal Summer Intraseasonal Oscillation are associated with positive height anomalies over CEC and SC, increasing HDE frequency by about 35-54% relative to the climatological mean. Understanding the effects of sub-seasonal and seasonal atmospheric circulation variability, such as the Silk Road Pattern and Boreal Summer Intraseasonal Oscillation, on HDEs is important to improve HDE predictions over China.

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 Characteristics of Large-Scale Circulation Affecting the Inter-Annual Precipitation Variability in Northern Sumatra Island during Boreal Summer

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 136
Author(s):  
Yahya Darmawan ◽  
Huang-Hsiung Hsu ◽  
Jia-Yuh Yu
Keyword(s):  
Large Scale ◽  
Precipitation Variability ◽  
Specific Humidity ◽  
Boreal Summer ◽  
Moisture Budget ◽  
Large Scale Circulation ◽  
Budget Analysis ◽  
Sumatra Island ◽  
Precipitation Anomalies ◽  
The Impact

This study aims to explore the contrasting characteristics of large-scale circulation that led to the precipitation anomalies over the northern parts of Sumatra Island. Further, the impact of varying the Asian–Australian Monsoon (AAM) was investigated for triggering the precipitation variability over the study area. The moisture budget analysis was applied to quantify the most dominant component that induces precipitation variability during the JJA (June, July, and August) period. Then, the composite analysis and statistical approach were applied to confirm the result of the moisture budget. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Anaysis Interim (ERA-Interim) from 1981 to 2016, we identified 9 (nine) dry and 6 (six) wet years based on precipitation anomalies, respectively. The dry years (wet years) anomalies over the study area were mostly supported by downward (upward) vertical velocity anomaly instead of other variables such as specific humidity, horizontal velocity, and evaporation. In the dry years (wet years), there is a strengthening (weakening) of the descent motion, which triggers a reduction (increase) of convection over the study area. The overall downward (upward) motion of westerly (easterly) winds appears to suppress (support) the convection and lead to negative (positive) precipitation anomaly in the whole region but with the largest anomaly over northern parts of Sumatra. The AAM variability proven has a significant role in the precipitation variability over the study area. A teleconnection between the AAM and other global circulations implies the precipitation variability over the northern part of Sumatra Island as a regional phenomenon. The large-scale tropical circulation is possibly related to the PWC modulation (Pacific Walker Circulation).

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