The contribution of tropical cyclones(TCs)to the East Asia–Pacific(EAP)teleconnection pattern during summer was investigated using the best track data of the Joint Typhoon Warning Center and NCEP-2 reanalysis dataset...The contribution of tropical cyclones(TCs)to the East Asia–Pacific(EAP)teleconnection pattern during summer was investigated using the best track data of the Joint Typhoon Warning Center and NCEP-2 reanalysis datasets from 1979 to2018.The results showed that the TCs over the western North Pacific(WNP)correspond to a strengthened EAP pattern:During the summers of strong convection over the tropical WNP,TC days correspond to a stronger cyclonic circulation anomaly over the WNP in the lower troposphere,an enhanced seesaw pattern of negative and positive geopotential height anomalies over the subtropical WNP and midlatitude East Asia in the middle troposphere,and a more northward shift of the East Asian westerly jet in the upper troposphere.Further analyses indicated that two types of TCs with distinctly different tracks,i.e.,westward-moving TCs and northward-moving TCs,both favor the EAP pattern.The present results imply that TCs over the WNP,as extreme weather,can contribute significantly to summer-mean climate anomalies over the WNP and East Asia.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
The current progresses in the study of impacts of the Tibetan Plateau on Asian summer climate in the last decade are reviewed. By analyzing evolution of the transitional zone between westerly to the north and easterly...The current progresses in the study of impacts of the Tibetan Plateau on Asian summer climate in the last decade are reviewed. By analyzing evolution of the transitional zone between westerly to the north and easterly to the south (WEB), it is shown that due to the strong heating over the Tibetan Plateau in spring, the overturning in the prevailing wind direction from easterly in winter to westerly in summer occurs firstly over the eastern Bay of Bengal (BOB), accompanied with vigorous convective precipitation to its east. The area between eastern BOB and western Indo-China Peninsula thus becomes the area with the earliest onset of Asian monsoon, which may be referred as BOB monsoon in short. It is shown that the summertime circulations triggered by the thermal forcing of the Iranian Plateau and the Tibetan Plateau are embedded in phase with the continental-scale circulation forced by the diabatic heating over the Eurasian Continent. As a result, the East Asian summer monsoon is intensified and the drought climate over the western and central Asian areas is enhanced. Together with perturbations triggered by the Tibetan Plateau, the above scenarios and the associated heating have important influences on the climate patterns over Asia. Furthermore, the characteristics of the Tibetan mode of the summertime South Asian high are compared with those of Iranian mode. Results demonstrate that corresponding to each of the bimodality of the South Asian high, the rainfall anomaly distributions over Asia exhibit different patterns.展开更多
Based on the NCEP DOE AMIP II daily reanalysis data (1979-2005), the evolution of the East Asia/Pacific (EAP) teleconnection pattern during the pre-rainy period of South China is studied on the medium-range time s...Based on the NCEP DOE AMIP II daily reanalysis data (1979-2005), the evolution of the East Asia/Pacific (EAP) teleconnection pattern during the pre-rainy period of South China is studied on the medium-range time scale. It is found that positive and negative EAP patterns share a similar generation process. In the middle and upper troposphere, Rossby wave packets emanating from the northeast Atlantic or Europe propagate toward East Asia along the Eurasian continent waveguide and finally give rise to the three anomaly centers of the EAP pattern over East Asia. Among the three anomaly centers, the western Pacific subtropical center appears the latest. Rossby wave packets propagate from the high latitude anomaly center toward the mid-latitude and the subtropical ones. The enhancement and maintenance of the subtropical anomaly center is closely associated with the subtropical jet waveguide and the incoming Rossby wave packets from the upstream. In the lower troposphere, Rossby wave packets emanate from the subtropical Asia toward East Asia. Positive and negative EAP patterns could not be regarded as "mirrors" to each other with simply reversed phase. For the positive pattern, the positive height anomaly center around the Scandinavia Peninsula keeps its strength and position during the mature period, and the Rossby wave packets thus propagate persistently toward East Asia, facilitating a longer mature time of the positive pattern. As for the formation of the negative EAP pattern, however, the incoming Rossby wave energy from the upstream contributes to both the enhancement and southeastward movement of the negative anomaly belt from the Yenisei River to the Bering Strait and the positive anomaly center around Mongolia. At the peak time, the two anomlous circulations are evolved into the Northeast Asia and the mid-latitude anomaly centers of the negative pattern, respectively. The energy dispersion of Rossby wave packets is relatively fast due to the predominant zonal circulation in the extratropics, causing a shorter mature period of the negative pattern. During the pre-rainy period of South China, the prevalence of the EAP pattern significantly affects the rainfall over the region south of the Yangtze River. The positive (negative) EAP pattern tends to cause positive (negative) precipitation anomalies in that region. This is different from the earlier research findings based on monthly mean data.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.41721004)。
文摘The contribution of tropical cyclones(TCs)to the East Asia–Pacific(EAP)teleconnection pattern during summer was investigated using the best track data of the Joint Typhoon Warning Center and NCEP-2 reanalysis datasets from 1979 to2018.The results showed that the TCs over the western North Pacific(WNP)correspond to a strengthened EAP pattern:During the summers of strong convection over the tropical WNP,TC days correspond to a stronger cyclonic circulation anomaly over the WNP in the lower troposphere,an enhanced seesaw pattern of negative and positive geopotential height anomalies over the subtropical WNP and midlatitude East Asia in the middle troposphere,and a more northward shift of the East Asian westerly jet in the upper troposphere.Further analyses indicated that two types of TCs with distinctly different tracks,i.e.,westward-moving TCs and northward-moving TCs,both favor the EAP pattern.The present results imply that TCs over the WNP,as extreme weather,can contribute significantly to summer-mean climate anomalies over the WNP and East Asia.
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 Basic Research Program of China under Grant No. 2005CB422004 Natural Science Foundation of China under Grant Nos. 40375022, 40325015, and 40475027
文摘The current progresses in the study of impacts of the Tibetan Plateau on Asian summer climate in the last decade are reviewed. By analyzing evolution of the transitional zone between westerly to the north and easterly to the south (WEB), it is shown that due to the strong heating over the Tibetan Plateau in spring, the overturning in the prevailing wind direction from easterly in winter to westerly in summer occurs firstly over the eastern Bay of Bengal (BOB), accompanied with vigorous convective precipitation to its east. The area between eastern BOB and western Indo-China Peninsula thus becomes the area with the earliest onset of Asian monsoon, which may be referred as BOB monsoon in short. It is shown that the summertime circulations triggered by the thermal forcing of the Iranian Plateau and the Tibetan Plateau are embedded in phase with the continental-scale circulation forced by the diabatic heating over the Eurasian Continent. As a result, the East Asian summer monsoon is intensified and the drought climate over the western and central Asian areas is enhanced. Together with perturbations triggered by the Tibetan Plateau, the above scenarios and the associated heating have important influences on the climate patterns over Asia. Furthermore, the characteristics of the Tibetan mode of the summertime South Asian high are compared with those of Iranian mode. Results demonstrate that corresponding to each of the bimodality of the South Asian high, the rainfall anomaly distributions over Asia exhibit different patterns.
基金Supported jointly by the 973 Project under Grant No. 2006CB403601the National Natural Science Foundation of Chinaunder Grant Nos. 40523001 and 40575024
文摘Based on the NCEP DOE AMIP II daily reanalysis data (1979-2005), the evolution of the East Asia/Pacific (EAP) teleconnection pattern during the pre-rainy period of South China is studied on the medium-range time scale. It is found that positive and negative EAP patterns share a similar generation process. In the middle and upper troposphere, Rossby wave packets emanating from the northeast Atlantic or Europe propagate toward East Asia along the Eurasian continent waveguide and finally give rise to the three anomaly centers of the EAP pattern over East Asia. Among the three anomaly centers, the western Pacific subtropical center appears the latest. Rossby wave packets propagate from the high latitude anomaly center toward the mid-latitude and the subtropical ones. The enhancement and maintenance of the subtropical anomaly center is closely associated with the subtropical jet waveguide and the incoming Rossby wave packets from the upstream. In the lower troposphere, Rossby wave packets emanate from the subtropical Asia toward East Asia. Positive and negative EAP patterns could not be regarded as "mirrors" to each other with simply reversed phase. For the positive pattern, the positive height anomaly center around the Scandinavia Peninsula keeps its strength and position during the mature period, and the Rossby wave packets thus propagate persistently toward East Asia, facilitating a longer mature time of the positive pattern. As for the formation of the negative EAP pattern, however, the incoming Rossby wave energy from the upstream contributes to both the enhancement and southeastward movement of the negative anomaly belt from the Yenisei River to the Bering Strait and the positive anomaly center around Mongolia. At the peak time, the two anomlous circulations are evolved into the Northeast Asia and the mid-latitude anomaly centers of the negative pattern, respectively. The energy dispersion of Rossby wave packets is relatively fast due to the predominant zonal circulation in the extratropics, causing a shorter mature period of the negative pattern. During the pre-rainy period of South China, the prevalence of the EAP pattern significantly affects the rainfall over the region south of the Yangtze River. The positive (negative) EAP pattern tends to cause positive (negative) precipitation anomalies in that region. This is different from the earlier research findings based on monthly mean data.