In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key r...In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes.Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east–west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific–Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.展开更多
This study investigated the fluctuations in the relationship between the Silk Road Pattern(SRP)and the boreal summer North Atlantic Oscillation(SNAO).The results indicated that the SRP–SNAO relationship was relativel...This study investigated the fluctuations in the relationship between the Silk Road Pattern(SRP)and the boreal summer North Atlantic Oscillation(SNAO).The results indicated that the SRP–SNAO relationship was relatively weak during 1958–2022,which was primarily due to fluctuations,particularly the reversal in their relationship since the late 1990s.Using wavelet coherence analysis,the authors identified a strong SRP–SNAO linkage on a 4–8-yr timescale,in particular during the mid-1970s to the early/mid-1990s.This strong linkage is mainly attributable to the intensification and eastward movement of the southern part of the SNAO around the mid/late 1970s,which favored the strong connection between the SNAO and the SRP.Additionally,the interdecadal changes of the atmospheric circulations over the North Atlantic and Eurasia around the mid/late 1970s that resembled the circulation anomalies related to the strong SRP–SNAO linkage,may also have provided a favorable background for the strong connection between the two teleconnections.These findings on the fluctuations in the SRP–SNAO linkage may offer important implications for understanding the impact of the SNAO on the SRP and the variability of the SRP.展开更多
In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet （JMD） and the Silk Road Pattern （SRP） in summer. The present study reveals that this relati...In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet （JMD） and the Silk Road Pattern （SRP） in summer. The present study reveals that this relationship is robust in northward JMD years but absent in southward JMD years. In other words, the amplitude of the SRP increases with northward displacement of the jet but shows little change with southward displacement. Further analysis indicates that, in northward JMD years, the Rossby wave source （RWS） anomalies, which are primarily contributed by the planetary vortex stretching, are significantly stronger around the entrance of the Asian jet, i.e., the Mediterranean Sea-Caspian Sea area, with the spatial distribution being consistent with that related to the SRP. By contrast, in southward JMD years, the RWS anomalies are much weaker. Therefore, this study suggests that the RWS plays a crucial role in inducing the asymmetry of the JMD-SRP relationship. The results imply that climate anomalies may be stronger in strongly northward-displaced JMD years due to the concurrence of the JMD and SRP, and thus more attention should be paid to these years.展开更多
In this study, two modes of the Silk Road pattern were investigated using NCEP2 reanalysis data and the simulation produced by Spectral Atmospheric Circulation Model of IAP LASG, Version 2 （SAMIL2.0） that was forced...In this study, two modes of the Silk Road pattern were investigated using NCEP2 reanalysis data and the simulation produced by Spectral Atmospheric Circulation Model of IAP LASG, Version 2 （SAMIL2.0） that was forced by SST observation data. The horizontal distribution of both modes were reasonably reproduced by the simulation, with a pattern correlation coefficient of 0.63 for the first mode and 0.62 for the second mode. The wave train was maintained by barotropic energy conversion （denoted as CK） and baroclinic energy conversion （denoted as CP） from the mean flow. The distribution of CK was dominated by its meridional component （CKy） in both modes. When integrated spatially, CKx was more efficient than its zonal component （CKx） in the first mode but less in the second mode. The distribution and efficiency of CK were not captured well by SAMIL2.0. However, the model performed reasonably well at reproducing the distribution and efficiency of CP in both modes. Because CP is more efficient than CK, the spatial patterns of the Silk Road pattern were well reproduced. Interestingly, the temporal phase of the second mode was well captured by a single-member simulation. However, further analysis of other ensemble runs demonstrated that the successful reproduction of the temporal phase was a result of internal variability rather than a signal of SST forcing. The analysis shows that the observed temporal variations of both CP and CK were poorly reproduced, leading to the low accuracy of the temporal phase of the Silk Road pattern in the simulation.展开更多
The Silk Road pattern（SRP）, which is a teleconnection pattern along the Asian upper-tropospheric westerly jet in summer, exhibits both interannual and decadal variabilities. Through the nineyear Gaussian filtering m...The Silk Road pattern（SRP）, which is a teleconnection pattern along the Asian upper-tropospheric westerly jet in summer, exhibits both interannual and decadal variabilities. Through the nineyear Gaussian filtering method and regression analyses, this study compares the interannual and decadal components of the SRP. The results indicate that the interannual SRP corresponds to a well-organized wave train of alternate cyclonic and anticyclonic anomalies across the Eurasian continent along the Asian westerly jet, resulting in a similar wave-like pattern of cold and warm surface temperature anomalies. This pattern of temperature anomalies differs from that associated with the original SRP, which is characterized by warmer or cooler temperatures mainly over Europe–West Asia and Northeast Asia, depending on the phase of the SRP. On the other hand, the decadal SRP shows a similar pattern to the interannual one from Europe to Central Asia, but the meridional wind anomalies tend to be weak over East Asia. These circulation anomalies are responsible for the significant temperature anomalies over Europe–West Asia and Northeast Asia but weak anomalies between these two domains.展开更多
The spring(April-May-June)Barents Sea ice has been proven to affect the summer surface air temperature over the Tibetan Plateau(TP).However,its impact on summer(June-July-August)TP precipitation,a crucial climate comp...The spring(April-May-June)Barents Sea ice has been proven to affect the summer surface air temperature over the Tibetan Plateau(TP).However,its impact on summer(June-July-August)TP precipitation,a crucial climate component,remains unexplored.We investigate the physical linkage between spring Barents Sea ice and subsequent summer TP precipitation from 1979 to 2018.Our results indicate that above-normal spring Barents Sea ice leads to excessive summer TP precipitation,and vice versa.During spring,more Barents Sea ice induces remarkable cooling and subsidence over there and surrounding areas.The cooling over the Barents Sea can persist into summer,triggering a meridional wave-like pattern along the longitude of 60°E and,in turn,an anomalous atmospheric subsidence over the Caspian Sea and the eastern region adjacent to it.This alters 200 h Pa convergence and modulates the Silk Road pattern(SRP).As a result,cyclonic anomalies form to the west of the TP,which enhance moisture transport toward the TP and increase its precipitation during summer.Numerical experiments reproduce these physical processes and further support our conclusions.展开更多
It is widely recognized that rainfall over the Yangtze River valley （YRV） strengthens considerably during the decaying summer of E1 Nifio, as demonstrated by the catastrophic flooding suffered in the summer of 1998....It is widely recognized that rainfall over the Yangtze River valley （YRV） strengthens considerably during the decaying summer of E1 Nifio, as demonstrated by the catastrophic flooding suffered in the summer of 1998. Nevertheless, the rainfall over the YRV in the summer of 2016 was much weaker than that in 1998, despite the intensity of the 2016 E1 Nifio having been as strong as that in 1998. A thorough comparison of the YRV summer rainfall anomaly between 2016 and 1998 suggests that the difference was caused by the sub-seasonal variation in the YRV rainfall anomaly between these two years, principally in August. The precipitation anomaly was negative in August 2016--different to the positive anomaly of 1998.展开更多
Extremely heavy rainfall occurred over both Northwest India and North China in September 2021.The precipitation anomalies were 4.1 and 6.2 times interannual standard deviation over the two regions,respectively,and bro...Extremely heavy rainfall occurred over both Northwest India and North China in September 2021.The precipitation anomalies were 4.1 and 6.2 times interannual standard deviation over the two regions,respectively,and broke the record since the observational data were available,i.e.,1901 for India and 1951 for China.In this month,the Asian uppertropospheric westerly jet was greatly displaced poleward over West Asia,and correspondingly,an anomalous cyclone appeared over India.The anomalous cyclone transported abundant water vapor into Northwest India,leading to the heavy rainfall there.In addition,the Silk Road pattern,a teleconnection pattern of upper-level meridional wind over the Eurasian continent and fueled by the heavy rainfall in Northwest India,contributed to the heavy rainfall in North China.Our study emphasizes the roles of atmospheric teleconnection patterns in concurrent rainfall extremes in the two regions far away from each other,and the occurrence of rainfall extremes during the post-or pre-monsoon period in the northern margins of monsoon regions.展开更多
This study investigated the large-scale circulation anomalies,in both the upper and lower troposphere,associated with the interannual variation of rainfall in Pakistan during summer,using the station observation data ...This study investigated the large-scale circulation anomalies,in both the upper and lower troposphere,associated with the interannual variation of rainfall in Pakistan during summer,using the station observation data in this country and circulation data of the NCEP−NCAR reanalysis from 1981 to 2017.Results showed that the upper-and lower-tropospheric circulation anomalies associated with monthly rainfall variability exhibit similar features from June to August,so analyses were performed on June−August circulation and Pakistan rainfall data.The analyzed results indicated that summer rainfall in Pakistan is enhanced when there is an anticyclonic anomaly to the northwest of Pakistan in the upper troposphere and easterly anomalies along the southern foothills of the Himalayas in the lower troposphere,and vice versa.These upper-and lower-tropospheric circulation anomalies were found to be related,but show unique features.The upper-tropospheric anticyclonic anomaly is closely related to the Silk Road Pattern along the Asian westerly jet,while the lower-tropospheric easterly anomalies are related to the cyclonic anomaly to the south of Pakistan,i.e.,intensified South Asian monsoon trough.The results presented here suggest that the interannual variability of summer rainfall in Pakistan is a combined result of upper-and lower-tropospheric circulation anomalies,and of extratropical and tropical circulation anomalies.展开更多
The brocades (jin 锦) in Han Dynasty is very precious for the study of the history of ancient Chinese textiles. This paper introduces the study on the brocades of Han Dynasty, which excavated from the tumuli of the an...The brocades (jin 锦) in Han Dynasty is very precious for the study of the history of ancient Chinese textiles. This paper introduces the study on the brocades of Han Dynasty, which excavated from the tumuli of the ancient nomadic tribe “Xiong-nu” (Hun 匈 奴) in the Noin-Ula Mountains in Mongolia. The detailed analyses of the brocades in the collection of Philadelphia Museum of Art are given in this paper and a logical, reasonable conjecture for ancient weaving technology is proposed.展开更多
This study investigates a cross-seasonal influence of the Silk Road Pattern（SRP）in July and discusses the related mechanism.Both the reanalysis and observational datasets indicate that the July SRP is closely relate...This study investigates a cross-seasonal influence of the Silk Road Pattern（SRP）in July and discusses the related mechanism.Both the reanalysis and observational datasets indicate that the July SRP is closely related to the following January temperature over East Asia during 1958/59–2001/02.Linear regression results reveal that,following a higher-than-normal SRP index in July,the Siberian high,Aleutian low,Urals high,East Asian trough,and meridional shear of the East Asian jet intensify significantly in January.Such atmospheric circulation anomalies are favorable for northerly wind anomalies over East Asia,leading to more southward advection of cold air and causing a decrease in temperature.Further analysis indicates that the North Pacific sea surface temperature anomalies（SSTAs）might play a critical role in storing the anomalous signal of the July SRP.The significant SSTAs related to the July SRP weaken in October and November,re-emerge in December,and strengthen in the following January.Such an SSTA pattern in January can induce a surface anomalous cyclone over North Pacific and lead to dominant convergence anomalies over northwestern Pacific.Correspondingly,significant divergence anomalies appear,collocated in the upper-level troposphere in situ.Due to the advection of vorticity by divergent wind,which can be regarded as a wave source,a stationary Rossby wave originates from North Pacific and propagates eastward to East Asia,leading to temperature anomalies through its influence on the large-scale atmospheric circulation.展开更多
Daily precipitation data from 149 rain gauge stations in China and NCEP-NCAR reanalysis data during 1961-2018are used to investigate the interdecadal variability of summer precipitation in Northwest China and related ...Daily precipitation data from 149 rain gauge stations in China and NCEP-NCAR reanalysis data during 1961-2018are used to investigate the interdecadal variability of summer precipitation in Northwest China and related causes.The results suggest that,on the interdecadal timescale,Northwest China shifts into a rainy period from the year 1987,with an increase in the precipitation amount and intensity;an increase in the probability of moderate rain,heavy rain,torrential rain,and extremely heavy rain;and a decrease in the probability of light rain.More than 60%of the increase in precipitation can be attributed to rainfall with intensity above the grade of heavy rain.The associated interdecadal variability of atmospheric circulations over midlatitude Eurasia in summer is examined and it is found that the interdecadal variability is mainly characterized by the Silk Road pattern(SRP),with a cyclonic circulation anomaly and an anticyclonic circulation anomaly over central Asia and Mongolia,respectively;enhanced ascending motion and atmospheric instability in Northwest China;and strengthened easterly winds caused by the Mongolian anticyclonic anomaly along the northern boundary of the Tibetan Plateau.On the south side of the Mongolian anticyclone,the water vapor transported from the Pacific and Indian Oceans as well as the South China Sea to Northwest China by easterly winds increases significantly,providing the main water vapor source for the increase in precipitation in Northwest China on the interdecadal timescale.The transition of the Atlantic multidecadal oscillation to a positive phase may be the main cause of the interdecadal transition of the SRP to a positive phase,resulting in the interdecadal increase in summer precipitation in Northwest China.展开更多
Tibetan Plateau(TP)precipitation is affected by anomalous circulation systems in both the tropics and mid-latitudes,due to the TP’s unique geographical location.By using observational,reanalysis,and CMIP6 model datas...Tibetan Plateau(TP)precipitation is affected by anomalous circulation systems in both the tropics and mid-latitudes,due to the TP’s unique geographical location.By using observational,reanalysis,and CMIP6 model datasets,this study reveals the individual and joint effects of the Indian Ocean Dipole(IOD)and Silk Road pattern(SRP)on the interannual variability of TP precipitation in September.In the positive IOD phase,the zonal gradient of the sea-surface temperature anomalies(SSTAs)drives a Gill-type response with an anticyclonic anomaly over the Indian subcontinent and Bay of Bengal.To the north,anomalous westerlies induce a shallow trough,and the associated anomalous southwesterlies transport moisture to the southeastern TP,resulting in surplus precipitation there.Meanwhile,the westerly jet disturbances over the North Atlantic excite an SRP-like pattern,resulting in a baroclinic structure in northern India with the upper(lower)tropospheric anomalous anticyclone(cyclone)over west-central Asia(northern India).The anomalous southwesterlies to the east of the low-level cyclone transport abundant moisture to the southeastern TP,which results in increased precipitation there.The joint effects of IOD and SRP can explain nearly 52%of the TP precipitation anomaly,exceeding the contribution of IOD(19%)and SRP(27%)alone.Our results highlight the necessity of considering the joint effects of drivers in the tropics and mid-latitudes,providing a basis for more accurate simulations and predictions of TP precipitation.展开更多
基金supported by the National Key R&D Program of China(Grant No.2016YFA0600703)the National Natural Science Foundation of China(Grant Nos.41605059,41505073 and 41375083)+1 种基金the Young Talent Support Program of the China Association for Science and Technology(Grant No.2016QNRC001)the Research Council of Norway SNOWGLACE(244166/E10)project
文摘In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes.Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east–west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific–Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.
基金jointly supported by the National Natural Science Foundation of China[grant numbers 41605058 and 41831175]the Joint Open Project of the Key Laboratory of Meteorological Disaster,the Ministry of Education,the Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters,NUIST[grant number KLME202104]。
文摘This study investigated the fluctuations in the relationship between the Silk Road Pattern(SRP)and the boreal summer North Atlantic Oscillation(SNAO).The results indicated that the SRP–SNAO relationship was relatively weak during 1958–2022,which was primarily due to fluctuations,particularly the reversal in their relationship since the late 1990s.Using wavelet coherence analysis,the authors identified a strong SRP–SNAO linkage on a 4–8-yr timescale,in particular during the mid-1970s to the early/mid-1990s.This strong linkage is mainly attributable to the intensification and eastward movement of the southern part of the SNAO around the mid/late 1970s,which favored the strong connection between the SNAO and the SRP.Additionally,the interdecadal changes of the atmospheric circulations over the North Atlantic and Eurasia around the mid/late 1970s that resembled the circulation anomalies related to the strong SRP–SNAO linkage,may also have provided a favorable background for the strong connection between the two teleconnections.These findings on the fluctuations in the SRP–SNAO linkage may offer important implications for understanding the impact of the SNAO on the SRP and the variability of the SRP.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41320104007, 41421004, and 41731177)
文摘In previous work, a significant relationship was identified between the meridional displacement of the Asian westerly jet （JMD） and the Silk Road Pattern （SRP） in summer. The present study reveals that this relationship is robust in northward JMD years but absent in southward JMD years. In other words, the amplitude of the SRP increases with northward displacement of the jet but shows little change with southward displacement. Further analysis indicates that, in northward JMD years, the Rossby wave source （RWS） anomalies, which are primarily contributed by the planetary vortex stretching, are significantly stronger around the entrance of the Asian jet, i.e., the Mediterranean Sea-Caspian Sea area, with the spatial distribution being consistent with that related to the SRP. By contrast, in southward JMD years, the RWS anomalies are much weaker. Therefore, this study suggests that the RWS plays a crucial role in inducing the asymmetry of the JMD-SRP relationship. The results imply that climate anomalies may be stronger in strongly northward-displaced JMD years due to the concurrence of the JMD and SRP, and thus more attention should be paid to these years.
基金supported jointly by National Program on Key Basic Research Project(Grant No.2010CB951904)the"Strategic Priority Research Program-Climate Change:Carbon Budget and Related Issues"of the Chinese Academy of Sciences(Grant No.XDA05110301)the National Natural Science Foundation of China(Grant Nos.40890054 and 41125017)
文摘In this study, two modes of the Silk Road pattern were investigated using NCEP2 reanalysis data and the simulation produced by Spectral Atmospheric Circulation Model of IAP LASG, Version 2 （SAMIL2.0） that was forced by SST observation data. The horizontal distribution of both modes were reasonably reproduced by the simulation, with a pattern correlation coefficient of 0.63 for the first mode and 0.62 for the second mode. The wave train was maintained by barotropic energy conversion （denoted as CK） and baroclinic energy conversion （denoted as CP） from the mean flow. The distribution of CK was dominated by its meridional component （CKy） in both modes. When integrated spatially, CKx was more efficient than its zonal component （CKx） in the first mode but less in the second mode. The distribution and efficiency of CK were not captured well by SAMIL2.0. However, the model performed reasonably well at reproducing the distribution and efficiency of CP in both modes. Because CP is more efficient than CK, the spatial patterns of the Silk Road pattern were well reproduced. Interestingly, the temporal phase of the second mode was well captured by a single-member simulation. However, further analysis of other ensemble runs demonstrated that the successful reproduction of the temporal phase was a result of internal variability rather than a signal of SST forcing. The analysis shows that the observed temporal variations of both CP and CK were poorly reproduced, leading to the low accuracy of the temporal phase of the Silk Road pattern in the simulation.
基金supported jointly by the National Natural Science Foundation of China[Grant numbers 41705044 and 41405053]
文摘The Silk Road pattern（SRP）, which is a teleconnection pattern along the Asian upper-tropospheric westerly jet in summer, exhibits both interannual and decadal variabilities. Through the nineyear Gaussian filtering method and regression analyses, this study compares the interannual and decadal components of the SRP. The results indicate that the interannual SRP corresponds to a well-organized wave train of alternate cyclonic and anticyclonic anomalies across the Eurasian continent along the Asian westerly jet, resulting in a similar wave-like pattern of cold and warm surface temperature anomalies. This pattern of temperature anomalies differs from that associated with the original SRP, which is characterized by warmer or cooler temperatures mainly over Europe–West Asia and Northeast Asia, depending on the phase of the SRP. On the other hand, the decadal SRP shows a similar pattern to the interannual one from Europe to Central Asia, but the meridional wind anomalies tend to be weak over East Asia. These circulation anomalies are responsible for the significant temperature anomalies over Europe–West Asia and Northeast Asia but weak anomalies between these two domains.
基金supported by the National Natural Science Foundation of China(Grant No.42221004)the Open Research Fund of TPESER(Grant No.TPESER202205)。
文摘The spring(April-May-June)Barents Sea ice has been proven to affect the summer surface air temperature over the Tibetan Plateau(TP).However,its impact on summer(June-July-August)TP precipitation,a crucial climate component,remains unexplored.We investigate the physical linkage between spring Barents Sea ice and subsequent summer TP precipitation from 1979 to 2018.Our results indicate that above-normal spring Barents Sea ice leads to excessive summer TP precipitation,and vice versa.During spring,more Barents Sea ice induces remarkable cooling and subsidence over there and surrounding areas.The cooling over the Barents Sea can persist into summer,triggering a meridional wave-like pattern along the longitude of 60°E and,in turn,an anomalous atmospheric subsidence over the Caspian Sea and the eastern region adjacent to it.This alters 200 h Pa convergence and modulates the Silk Road pattern(SRP).As a result,cyclonic anomalies form to the west of the TP,which enhance moisture transport toward the TP and increase its precipitation during summer.Numerical experiments reproduce these physical processes and further support our conclusions.
基金supported by the National Natural Science Foundation of China (Grant Nos.41320104007,U1502233,41675078 and 41461164005)
文摘It is widely recognized that rainfall over the Yangtze River valley （YRV） strengthens considerably during the decaying summer of E1 Nifio, as demonstrated by the catastrophic flooding suffered in the summer of 1998. Nevertheless, the rainfall over the YRV in the summer of 2016 was much weaker than that in 1998, despite the intensity of the 2016 E1 Nifio having been as strong as that in 1998. A thorough comparison of the YRV summer rainfall anomaly between 2016 and 1998 suggests that the difference was caused by the sub-seasonal variation in the YRV rainfall anomaly between these two years, principally in August. The precipitation anomaly was negative in August 2016--different to the positive anomaly of 1998.
基金supported by the National Natural Science Foundation of China(Grant No.42105064)the Second Tibetan Plateau Scientific Expedition and Research(STEP)program(Grant No.2019QZKK0102)China Meteorological Administration program(Grant No.CXFZ2021J030)。
文摘Extremely heavy rainfall occurred over both Northwest India and North China in September 2021.The precipitation anomalies were 4.1 and 6.2 times interannual standard deviation over the two regions,respectively,and broke the record since the observational data were available,i.e.,1901 for India and 1951 for China.In this month,the Asian uppertropospheric westerly jet was greatly displaced poleward over West Asia,and correspondingly,an anomalous cyclone appeared over India.The anomalous cyclone transported abundant water vapor into Northwest India,leading to the heavy rainfall there.In addition,the Silk Road pattern,a teleconnection pattern of upper-level meridional wind over the Eurasian continent and fueled by the heavy rainfall in Northwest India,contributed to the heavy rainfall in North China.Our study emphasizes the roles of atmospheric teleconnection patterns in concurrent rainfall extremes in the two regions far away from each other,and the occurrence of rainfall extremes during the post-or pre-monsoon period in the northern margins of monsoon regions.
基金the National Natural Science Foundation of China(Grant Nos.41705044 and 41721004)the Joint Open Project of KLME and CIC-FEMD(Grant No.KLME201802)the second Tibetan Plateau Scientific Expedition and Research(STEP)Program(Grant No.2019QZKK0102).
文摘This study investigated the large-scale circulation anomalies,in both the upper and lower troposphere,associated with the interannual variation of rainfall in Pakistan during summer,using the station observation data in this country and circulation data of the NCEP−NCAR reanalysis from 1981 to 2017.Results showed that the upper-and lower-tropospheric circulation anomalies associated with monthly rainfall variability exhibit similar features from June to August,so analyses were performed on June−August circulation and Pakistan rainfall data.The analyzed results indicated that summer rainfall in Pakistan is enhanced when there is an anticyclonic anomaly to the northwest of Pakistan in the upper troposphere and easterly anomalies along the southern foothills of the Himalayas in the lower troposphere,and vice versa.These upper-and lower-tropospheric circulation anomalies were found to be related,but show unique features.The upper-tropospheric anticyclonic anomaly is closely related to the Silk Road Pattern along the Asian westerly jet,while the lower-tropospheric easterly anomalies are related to the cyclonic anomaly to the south of Pakistan,i.e.,intensified South Asian monsoon trough.The results presented here suggest that the interannual variability of summer rainfall in Pakistan is a combined result of upper-and lower-tropospheric circulation anomalies,and of extratropical and tropical circulation anomalies.
文摘The brocades (jin 锦) in Han Dynasty is very precious for the study of the history of ancient Chinese textiles. This paper introduces the study on the brocades of Han Dynasty, which excavated from the tumuli of the ancient nomadic tribe “Xiong-nu” (Hun 匈 奴) in the Noin-Ula Mountains in Mongolia. The detailed analyses of the brocades in the collection of Philadelphia Museum of Art are given in this paper and a logical, reasonable conjecture for ancient weaving technology is proposed.
基金Supported by the National Key Research and Development Program of China(2016YFA0600703)National Natural Science Foundation of China(41505073)
文摘This study investigates a cross-seasonal influence of the Silk Road Pattern（SRP）in July and discusses the related mechanism.Both the reanalysis and observational datasets indicate that the July SRP is closely related to the following January temperature over East Asia during 1958/59–2001/02.Linear regression results reveal that,following a higher-than-normal SRP index in July,the Siberian high,Aleutian low,Urals high,East Asian trough,and meridional shear of the East Asian jet intensify significantly in January.Such atmospheric circulation anomalies are favorable for northerly wind anomalies over East Asia,leading to more southward advection of cold air and causing a decrease in temperature.Further analysis indicates that the North Pacific sea surface temperature anomalies（SSTAs）might play a critical role in storing the anomalous signal of the July SRP.The significant SSTAs related to the July SRP weaken in October and November,re-emerge in December,and strengthen in the following January.Such an SSTA pattern in January can induce a surface anomalous cyclone over North Pacific and lead to dominant convergence anomalies over northwestern Pacific.Correspondingly,significant divergence anomalies appear,collocated in the upper-level troposphere in situ.Due to the advection of vorticity by divergent wind,which can be regarded as a wave source,a stationary Rossby wave originates from North Pacific and propagates eastward to East Asia,leading to temperature anomalies through its influence on the large-scale atmospheric circulation.
基金Supported by the National Key Research and Development Program of China(2017YFA0605004)National Natural Science Foundation of China(41775082 and 41975100)。
文摘Daily precipitation data from 149 rain gauge stations in China and NCEP-NCAR reanalysis data during 1961-2018are used to investigate the interdecadal variability of summer precipitation in Northwest China and related causes.The results suggest that,on the interdecadal timescale,Northwest China shifts into a rainy period from the year 1987,with an increase in the precipitation amount and intensity;an increase in the probability of moderate rain,heavy rain,torrential rain,and extremely heavy rain;and a decrease in the probability of light rain.More than 60%of the increase in precipitation can be attributed to rainfall with intensity above the grade of heavy rain.The associated interdecadal variability of atmospheric circulations over midlatitude Eurasia in summer is examined and it is found that the interdecadal variability is mainly characterized by the Silk Road pattern(SRP),with a cyclonic circulation anomaly and an anticyclonic circulation anomaly over central Asia and Mongolia,respectively;enhanced ascending motion and atmospheric instability in Northwest China;and strengthened easterly winds caused by the Mongolian anticyclonic anomaly along the northern boundary of the Tibetan Plateau.On the south side of the Mongolian anticyclone,the water vapor transported from the Pacific and Indian Oceans as well as the South China Sea to Northwest China by easterly winds increases significantly,providing the main water vapor source for the increase in precipitation in Northwest China on the interdecadal timescale.The transition of the Atlantic multidecadal oscillation to a positive phase may be the main cause of the interdecadal transition of the SRP to a positive phase,resulting in the interdecadal increase in summer precipitation in Northwest China.
基金supported by the National Natural Science Foundation of China(Grants Nos.41725018,91937302,&42030602)。
文摘Tibetan Plateau(TP)precipitation is affected by anomalous circulation systems in both the tropics and mid-latitudes,due to the TP’s unique geographical location.By using observational,reanalysis,and CMIP6 model datasets,this study reveals the individual and joint effects of the Indian Ocean Dipole(IOD)and Silk Road pattern(SRP)on the interannual variability of TP precipitation in September.In the positive IOD phase,the zonal gradient of the sea-surface temperature anomalies(SSTAs)drives a Gill-type response with an anticyclonic anomaly over the Indian subcontinent and Bay of Bengal.To the north,anomalous westerlies induce a shallow trough,and the associated anomalous southwesterlies transport moisture to the southeastern TP,resulting in surplus precipitation there.Meanwhile,the westerly jet disturbances over the North Atlantic excite an SRP-like pattern,resulting in a baroclinic structure in northern India with the upper(lower)tropospheric anomalous anticyclone(cyclone)over west-central Asia(northern India).The anomalous southwesterlies to the east of the low-level cyclone transport abundant moisture to the southeastern TP,which results in increased precipitation there.The joint effects of IOD and SRP can explain nearly 52%of the TP precipitation anomaly,exceeding the contribution of IOD(19%)and SRP(27%)alone.Our results highlight the necessity of considering the joint effects of drivers in the tropics and mid-latitudes,providing a basis for more accurate simulations and predictions of TP precipitation.
