The unprecedented Zhengzhou heavy rainfall in July 2021 occurred under the background of a northward shift of the western Pacific subtropical high(WPSH).Although the occurrence of this extreme event could not be captu...The unprecedented Zhengzhou heavy rainfall in July 2021 occurred under the background of a northward shift of the western Pacific subtropical high(WPSH).Although the occurrence of this extreme event could not be captured by seasonal predictions,a skillful prediction of the WPSH variation might have warned us of the increased probability of extreme weather events in Central and Northern China.However,the mechanism for the WPSH variation in July 2021 and its seasonal predictability are still unknown.Here,the observed northward shift of the WPSH in July 2021 is shown to correspond to a meridional dipole pattern of the 850-hPa geopotential height to the east of China,the amplitude of which became the strongest since 1979.The meridional dipole pattern is two nodes of the Pacific–Japan pattern.To investigate the predictability of the WPSH variation,a 21-member ensemble of seasonal predictions initiated from the end of June 2021 was conducted.The predictable and unpredictable components of the meridional dipole pattern were identified from the ensemble simulations.Its predictable component is driven by positive precipitation anomalies over the tropical western Pacific.The positive precipitation anomalies are caused by positive horizonal advection of the mean moist enthalpy by southwesterly anomalies to the northwestern flank of anticyclonic anomalies excited by the existing La Niña,which is skillfully predicted by the model.The leading mode of the unpredictable component is associated with the atmospheric internal intraseasonal oscillations,which are not initialized in the simulations.The relative contributions of the predictable and unpredictable components to the observed northward shift of the WPSH at 850 hPa are 28.0%and 72.0%,respectively.展开更多
The impact of surface sensible heating over the Tibetan Plateau （SHTP） on the western Pacific subtropical high （WPSH） with and without air-sea interaction was investigated in this study. Data analysis indicated th...The impact of surface sensible heating over the Tibetan Plateau （SHTP） on the western Pacific subtropical high （WPSH） with and without air-sea interaction was investigated in this study. Data analysis indicated that SHTP acts as a relatively independent factor in modulating the WPSH anomaly compared with ENSO events. Stronger spring SHTP is usually fol- lowed by an enhanced and westward extension of the WPSH in summer, and vice versa. Numerical experiments using both an AGCM and a CGCM confirmed that SHTP influences the large-scale circulation anomaly over the Pacific, which features a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to different background circulation in spring and summer, such a response facilitates a subdued WPSH in spring but an en- hanced WPSH in summer. Moreover, the CGCM results showed that the equatorial low-level westerly at the south edge of the cyclonic anomaly brings about a warm SST anomaly （SSTA） in the equatorial central Pacific via surface warm advection. Subsequently, an atmospheric Rossby wave is stimulated to the northwest of the warm SSTA, which in turn enhances the at- mospheric dipole anomalies over the western Pacific. Therefore, the air-sea feedbacks involved tend to reinforce the effect of SHTP on the WPSH anomaly, and the role of SHTP on general circulation needs to be considered in a land-air-sea interaction framework.展开更多
In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This re...In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.展开更多
By adopting characteristic index data for the Western Pacific Subtropical High(WPSH) from the National Climate Center of China, U.S. National Centers for Environmental Prediction-National Center for Atmospheric Resear...By adopting characteristic index data for the Western Pacific Subtropical High(WPSH) from the National Climate Center of China, U.S. National Centers for Environmental Prediction-National Center for Atmospheric Research(NCEP/NCAR) reanalysis data, and the National Oceanic and Atmospheric Administration(NOAA) sea surface temperature(SST) data, we studied the WPSH variability considering the background of climate warming by using a Gaussian filter, moving averages, correlation analysis, and synthetic analysis. Our results show that with climate warming over the past 60 years, significant changes in the WPSH include its enlarged area, strengthened intensity,westward extended ridge point and southward expanded southern boundary, as well as enhanced interannual fluctuations in all these indices. The western ridge point of the WPSH consistently varies with temperature changes in the Northern Hemisphere, but the location of the ridgeline varies independently. The intensity and area of the WPSH were both significantly increased in the late 1980 s. Specifically, the western ridge point started to significantly extend westward in the early 1990 s, and the associated interannual variability had a significant increase in the late 1990 s; in addition, the ridgeline was swaying along the north-south-north direction, and the corresponding variability was also greatly enhanced in the late 1990 s. With climate warming, the SST increase becomes more weakly correlated with the WPSH intensity enhancement but more strongly correlated with the westward extension of the ridge point in the equatorial central and eastern Pacific Ocean in winter, corresponding to an expanding WPSH in space. In the northern Pacific in winter, the SST decrease has a weaker correlation with the southerly location of the ridgeline but also a stronger correlation with the westward extension of the ridge point. In the tropical western Pacific in winter, the correlations of the SST decrease with the WPSH intensity enhancement, and the westward extension of the ridge point is strengthened. These observations can be explained by strengthened Hadley circulations, the dominant effects of the southward shift, and additional effects of the weakened ascending branch of the Walker circulation during warm climatological periods,which consequently lead to strengthened intensities, increased areas, and southward expansions of the WPSH in summer.展开更多
A case is reported, during which the Subtropical High over the Western Pacific (hereafter, SHWP in abbreviation) shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments onSHWP a...A case is reported, during which the Subtropical High over the Western Pacific (hereafter, SHWP in abbreviation) shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments onSHWP activity influenced by the heating over south Asia monsoon area are carried out, and the statistic significance of the results is checked. The results indicate that the enhancement of positive heating over South Asia willmotivate a wave-like series of anomaly centers, which propagate northeastward from the maximum heating center.so that a strong positive potential height anomaly center will set up from North China to Japan at Day X resultingin the enhancement of SHWP. Comparison of the influence upon SHWP by the heating over south Asia monsoonarea with that over ITCZ area south to SHWP is also carried out. It is pointed out that the heating over South Asiamonsoon area tends to favor SHWP north\vard movement while the heating over ITCZ area tends to thvor SHWPwestward stretching. As for the time to begin to influence on SHWP, the heating over south Asia monsoon areafavors the enhancement of SHWP atter Day 3 while that over ITCZ south to SHWP effects atter Day 5.展开更多
Index series of Subtropical High over the western Pacific was extended to AD 1880 by using of statistical and modeling method. Reconstructed indices by both methods show good accordance each other. Association of the ...Index series of Subtropical High over the western Pacific was extended to AD 1880 by using of statistical and modeling method. Reconstructed indices by both methods show good accordance each other. Association of the indices to the rainfall patterns over eastern China indicated the robustness of the reconstructions.展开更多
It is well known that on the interannual timescale,the westward extension of the western North Pacific subtropical high(WNPSH)results in enhanced rainfall over the Yangtze River basin(YRB)in summer,and vice versa.This...It is well known that on the interannual timescale,the westward extension of the western North Pacific subtropical high(WNPSH)results in enhanced rainfall over the Yangtze River basin(YRB)in summer,and vice versa.This study identifies that this correspondence experiences a decadal change in the late 1970s.That is,the WNPSH significantly affects YRB precipitation(YRBP)after the late 1970s(P2)but not before the late 1970s(P1).It is found that enhanced interannual variability of the WNPSH favors its effect on YRB rainfall in P2.On the other hand,after removing the strong WNPSH cases in P2 and making the WNPSH variability equivalent to that in P1,the WNPSH can still significantly affect YRB rainfall,suggesting that the WNPSH variability is not the only factor that affects the WNPSH-YRBP relationship.Further results indicate that the change in basic state of thermal conditions in the tropical WNP provides a favorable background for the enhanced WNPSH-YRBP relationship.In P2,the lower-tropospheric atmosphere in the tropical WNP gets warmer and wetter,and thus the meridional gradient of climatological equivalent potential temperature over the YRB is enhanced.As a result,the WNPSH-related circulation anomalies can more effectively induce YRB rainfall anomalies through affecting the meridional gradient of equivalent potential temperature over the YRB.展开更多
The NCEP/NCAR II daily mean reanalysis data and observed precipitation data are employed to investigate the westward extension of the western Pacific subtropical high (WPSH) during the heavy rain period over the south...The NCEP/NCAR II daily mean reanalysis data and observed precipitation data are employed to investigate the westward extension of the western Pacific subtropical high (WPSH) during the heavy rain period over the southern China in June 2005. Results show that there may exist a relationship between the east-west shift of the WPSH and the process of a southern China heavy rain. The analysis indicates that the vertical motion in the WPSH area is mainly caused by the latent heat release of monsoon rain belts on its northern and southern sides. The vertical motion could cause the accumulation of air mass in the center and west of the WPSH, which leads to its strengthening. The appearance of the northern and southern monsoon rain belts could not only enhance the WPSH by strengthening the descending draft, but also excite the development of positive vorticity and restrict the WPSH's movement in the north-south direction. Moreover, the Indian monsoon rainfall to the west of the WPSH may excite the development of anticyclonic vorticity on its eastern side, which leads to the westward extension of the WPSH.展开更多
Numerical experiments are carried out using a global spectral model to study the role of an ideal heating source over the western tropical Pacific region in a medium-term weather process that marks the western advance...Numerical experiments are carried out using a global spectral model to study the role of an ideal heating source over the western tropical Pacific region in a medium-term weather process that marks the western advancement of the subtropical high in mid-June 1979. The result has indicated that the effect of the ideal heating source is evident in about 4 days after the inclusion in the high and the circulation at mid-and high-latitudes over the eastern part of China; the disturbance produced over the tropical ocean first transfers towards the northwest along the easterly flow on the southern edge of the subtropical high and then divides into two branches as it moves over the westerly over the mid-latitude area, one continuing the journey northwestward and the other turning to the northeast by east, resulting in changes in the subtropical high and the westerly through combined action.展开更多
In this paper, using the daily grid data (2.5 × 2.5) of the ECMWF / WMO, we have computed respectively the three-dimensional wave activity flux in the stages of pre-onset, prevailing and post ending of Meiyu from...In this paper, using the daily grid data (2.5 × 2.5) of the ECMWF / WMO, we have computed respectively the three-dimensional wave activity flux in the stages of pre-onset, prevailing and post ending of Meiyu from 1 to 31 July 1982. The potential vorticity field is taken as the physical quantity relating the wave activity flux to the variation of the subtropical high over the Western Pacific. It is found that the three-dimensional wave activity flux is a powerful means for diagnosis of the variation of the subtropical high over the Western Pacific: The region of the subtropical high is just the confluence area of wave energy, whose changes in intensity and range decide the variation of the subtropical high. The confluence of wave energy comes from the monsoon flow in low latitudes, the Meiyu rain belts in middle latitudes and the heating fields on the eastern side of the Qinghai-Xizang Plateau. The relation between these sources and the subtropical high displays the self-adjusting mechanism among members of East-Asia summer monsoon.展开更多
The interdecadal variation of the summer western Pacific subtropical high(WPSH)during1948–2009 is investigated in this study.Compared with most previous works,which focused on the 500 h Pa geopotential height,the int...The interdecadal variation of the summer western Pacific subtropical high(WPSH)during1948–2009 is investigated in this study.Compared with most previous works,which focused on the 500 h Pa geopotential height,the interdecadal variation of the horizontal winds,relative vorticity,and eddy geopotential height over the western Pacific are all analyzed.The weakened anticyclone and decreased negative relative vorticity at middle-low levels over the western Pacific suggest that the WPSH weakened during 1979–2009 relative to1948–78.After subtracting the zonal belt mean height between 0°and 40°N,the 500 hP a eddy geopotential height with significant negative anomalies over the western Pacific can correctly depict this weakened interdecadal variation of the WPSH.The illusory westward extension signal reflected by the 500 h Pa geopotential height may derive from the significant increment of the geopotential height at middle and lower latitudes in the late 1970s under global warming.展开更多
Based on the pentad mean ridgeline index of the western Pacific subtropical high (WPSH), the authors identified the two northward jumps of the WPSH from 1979 to 2008 and revealed their associations with the tropical S...Based on the pentad mean ridgeline index of the western Pacific subtropical high (WPSH), the authors identified the two northward jumps of the WPSH from 1979 to 2008 and revealed their associations with the tropical SST anomalies. The authors show that the northward jumps, especially the second jump, exhibited remarkable interannual variability. In addition, the authors find that the two northward jumps were mutually independent and were influenced by the SST anomalies in the different regions of the tropical Pacific. The first jump was positively correlated with the SST anomalies in the tropical central Pacific from the preceding winter to June. In contrast, the second jump was positively related to ENSO in the preceding winter, but this correlation tended to weaken with the decay of ENSO and disappeared in July. Instead, a positive correlation was found in the Indian Ocean. We therefore suggest that ENSO plays an indirect role in the second jump through the capacitor effect of the Indian Ocean.展开更多
By use of the filter analysis technique, the Complex Empirical Othogonal Function (CEOF) method and the ECMWF/WMO 2.5°×2.5°grid data of the geopotential heights during the summer months in 1988, an inte...By use of the filter analysis technique, the Complex Empirical Othogonal Function (CEOF) method and the ECMWF/WMO 2.5°×2.5°grid data of the geopotential heights during the summer months in 1988, an interseasonal process that the western Pacific subtropical high (WPSH) was anomalously far to the north in the first and second ten days of July is studied. It has been found that in the western Pacific subtropical region in the first and second ten days of July,it is the continuous assembly of low frequency geopotential waves (LFGWs) that leads to the abnormality of WPSH. This abnormality emerges with the enhancement of wave assembling and ceases while the wave assembling situation disappears. The structure of the low frequency assembling waves corresponds to the structure of subtropical high in its abnormal period. The effect of the assembling waves on the abnormality of subtropical high can be considered as the accumulation of disturbance energy carried by the low frequency waves from different directions in the western Pacific region.展开更多
Using NCEP/NCAR daily reanalysis data and SCSMEX data, an investigation is carried out of the relationship between the position variation of the west Pacific subtropical high （WPSH） and the apparcnt heating in June ...Using NCEP/NCAR daily reanalysis data and SCSMEX data, an investigation is carried out of the relationship between the position variation of the west Pacific subtropical high （WPSH） and the apparcnt heating in June 1998 based on the complete vertical vorticlty equation. It is tbund that the non-adiabatic heating plays an important role in the position variation of WPSH. In comparison with climatic mean status, the vertical change of non-adiabatic heating is stronger in the north side of WPSH in June 1998, but weaker in the south side of WPSH. The anomalous non-uniform heating induces anomalous cyclonic vorticity in South China, areas to lhe south of the Yangtze and its mid-lower valleys, but anomalous anticyclonic vorticity in the Indo-China Peninsula and South China Sea areas lead to the more southward position of WPSH than the mean.展开更多
Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies ar...Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies are found for the time prior to 1980. The west Pacific subtropical high in the NCEP/NCAR data is less intense than in ECMWF data before 1980. The range and strength of the west Pacific subtropical high variation described by the NCEP/NCAR data are larger than those depicted by ECMWF data. The same situation appears in the 100-hPa geopotential field. These discoveries suggest that the interdecadal variation of the two systems as shown by the NCEP/NCAR data may not be true. Besides, the South Asia High center in the NCEP/NCAR data is obviously stronger than in the ECMWF data during the periods 1969, 1979-1991 and 1992-1995. Furthermore, the range is larger from 1992 to 1995.展开更多
1 INTRODUCTION In summer, different assembly of the intensity, location and vertical structure of the subtropical high and the earlier/later time of its seasonal northwards jump bring about different precipitation pat...1 INTRODUCTION In summer, different assembly of the intensity, location and vertical structure of the subtropical high and the earlier/later time of its seasonal northwards jump bring about different precipitation patterns over China. Therefore, subtropical high activity and its cause during the occurrence of extreme climatic event over China and the cause of China drought/flood are studied to improve weather forecasting.展开更多
This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high(WNPSH)and the East Asian westerly jet(EAJ)in summer on interan...This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high(WNPSH)and the East Asian westerly jet(EAJ)in summer on interannual timescales.The in-phase configuration of the WNPSH and EAJ is characterized by the westward(eastward)extension of the WNPSH and the southward(northward)shift of the EAJ,which is consistent with the general correspondence between their variations.The out-of-phase configuration includes the residual cases.We find that the in-phase configuration manifests itself as a typical meridional teleconnection.For instance,there is an anticyclonic(cyclonic)anomaly over the tropical western North Pacific and a cyclonic(anticyclonic)anomaly over the mid-latitudes of East Asia in the lower troposphere.These circulation anomalies are more conducive to rainfall anomalies over the Yangtze River basin and south Japan than are the individual WNPSH or EAJ.By contrast,for the out-of-phase configuration,the mid-latitude cyclonic(anticyclonic)anomaly is absent,and the lower-tropospheric circulation anomalies feature an anticyclonic(cyclonic)anomaly with a large meridional extension.Correspondingly,significant rainfall anomalies move northward to North China and the northern Korean Peninsula.Further results indicate that the out-of-phase configuration is associated with the developing phase of ENSO,with strong and significant sea surface temperature(SST)anomalies in the tropical central and eastern Pacific which occur simultaneously during summer and persist into the following winter.This is sharply different from the in-phase configuration,for which the tropical SSTs are not a necessity.展开更多
By using NCEP/NCAR daily reanalysis data and daily precipitation data of 740 stations in China, relationships between the position variation of the West Pacific subtropical high (WPSH) and the diabatic heating during ...By using NCEP/NCAR daily reanalysis data and daily precipitation data of 740 stations in China, relationships between the position variation of the West Pacific subtropical high (WPSH) and the diabatic heating during persistent and intense rains in the Yangtze-Huaihe Rivers basin are studied. The results show that the position variation of WPSH is closely associated with the diabatic heating. There are strong apparent heating sources and moisture sinks in both the basin (to the north of WPSH) and the north of Bay of Bengal (to the west of WPSH) during persistent and intense rain events. In the basin, Q 1z begins to increase 3 days ahead of intense rainfall, maximizes 2 days later and then reduces gradually, but it changes little after precipitation ends, thus preventing the WPSH from moving northward. In the north of Bay of Bengal, 2 days ahead of strong rainfall over the basin, Q 1z starts to increase and peaks 1 day after the rain occurs, leading to the westward extension of WPSH. Afterwards, Q 1z begins declining and the WPSH makes its eastward retreat accordingly. Based on the complete vertical vorticity equation, in mid-troposphere, the vertical variation of heating in the basin is favorable to the increase of cyclonic vorticity north of WPSH, which counteracts the northward movement of WPSH and favors the persistence of rainbands over the basin. The vertical variation of heating in the north of Bay of Bengal is in favor of the increase of anti-cyclonic vorticity to the west of WPSH, which induces the westward extension of WPSH.展开更多
This paper explores the impact of the convective action over the low-latitude region, the water vapor transport around the West Pacific subtropical high (WPSH), and its convective action on the seasonal northward jump...This paper explores the impact of the convective action over the low-latitude region, the water vapor transport around the West Pacific subtropical high (WPSH), and its convective action on the seasonal northward jump and southward withdrawal of the WPSH in summer by using the daily data set of NCEP and TBB for 1998. The research shows that in summer, the WPSH moves northward when the convection over the low-latitude tropical region intensifies and the subsidence region of the meridional vertically vertical circulation in meridional direction circulation over the region of 110?150癊 moves northward. Furthermore, as revealed by diagnostic analysis, the subtropical high moves northward after the obvious weakening of the longitudinal water vapor transport over the region around the subtropical high, but withdraws southward a pentad after the reduction of the latitudinal water vapor transport over the tropical West Pacific region. The research results show that the northward jump and southward withdrawal of the WPSH are closely related to the release of the convective latent heat at low latitudes and the water vapor transport at boundaries around WPSH and its convective action. The numerical simulation further validates the above-mentioned correlation between the variation of the action of the subtropical high and the preceding water vapor transport along with the convection characteristics.展开更多
By using ECMWF (2. 5°×2. 5°) grid data, analyzing correlation for the summer (June-August) of 1980 (the West Pacific Subtropical High (WPSH) anomalously more to the south), 1988 (the WPSH anomalously mo...By using ECMWF (2. 5°×2. 5°) grid data, analyzing correlation for the summer (June-August) of 1980 (the West Pacific Subtropical High (WPSH) anomalously more to the south), 1988 (the WPSH anomalously more to the north), 1981 (normal) in the west Pacific area, distribution characteristics of the low frequency waves are discussed. The relationship between distribution of the low frequency waves and intraseasonal abnormality of the west subtropical high is also analyzed. There is some discussions:(1)If the WPSH acts anomalously in summer, there is a distinct zonal wave series in the subtropical zone of the north Pacific.(2) One of the important characteristics of the WPSH abnormality is that there are low frequency geopotential high centres from east Pacific and northeast Asia, being combined in the west Pacific area.For different circulation, the combination areas are different, which define the WSPH anomalously more to the north or south.展开更多
基金supported by the National Natural Science Foundation of China under Grant No.41988101the Chinese Academy of Sciences under Grant XDA20060102the China Postdoctoral Science Foundation under Grant No.2022T150638 and K.C.Wong Education Foundation.
文摘The unprecedented Zhengzhou heavy rainfall in July 2021 occurred under the background of a northward shift of the western Pacific subtropical high(WPSH).Although the occurrence of this extreme event could not be captured by seasonal predictions,a skillful prediction of the WPSH variation might have warned us of the increased probability of extreme weather events in Central and Northern China.However,the mechanism for the WPSH variation in July 2021 and its seasonal predictability are still unknown.Here,the observed northward shift of the WPSH in July 2021 is shown to correspond to a meridional dipole pattern of the 850-hPa geopotential height to the east of China,the amplitude of which became the strongest since 1979.The meridional dipole pattern is two nodes of the Pacific–Japan pattern.To investigate the predictability of the WPSH variation,a 21-member ensemble of seasonal predictions initiated from the end of June 2021 was conducted.The predictable and unpredictable components of the meridional dipole pattern were identified from the ensemble simulations.Its predictable component is driven by positive precipitation anomalies over the tropical western Pacific.The positive precipitation anomalies are caused by positive horizonal advection of the mean moist enthalpy by southwesterly anomalies to the northwestern flank of anticyclonic anomalies excited by the existing La Niña,which is skillfully predicted by the model.The leading mode of the unpredictable component is associated with the atmospheric internal intraseasonal oscillations,which are not initialized in the simulations.The relative contributions of the predictable and unpredictable components to the observed northward shift of the WPSH at 850 hPa are 28.0%and 72.0%,respectively.
基金supported jointly by the National Natural Science Foundation of China(Grant No.91337216)the Special Fund for Public Welfare Industry(Meteorology),administered by the Chinese Ministry of Finance and the Ministry of Science and Technology(Grant No.GYHY201406001)the CAS XDA(Grant No.11010402)
文摘The impact of surface sensible heating over the Tibetan Plateau （SHTP） on the western Pacific subtropical high （WPSH） with and without air-sea interaction was investigated in this study. Data analysis indicated that SHTP acts as a relatively independent factor in modulating the WPSH anomaly compared with ENSO events. Stronger spring SHTP is usually fol- lowed by an enhanced and westward extension of the WPSH in summer, and vice versa. Numerical experiments using both an AGCM and a CGCM confirmed that SHTP influences the large-scale circulation anomaly over the Pacific, which features a barotropic anticyclonic response over the northwestern Pacific and a cyclonic response to the south. Owing to different background circulation in spring and summer, such a response facilitates a subdued WPSH in spring but an en- hanced WPSH in summer. Moreover, the CGCM results showed that the equatorial low-level westerly at the south edge of the cyclonic anomaly brings about a warm SST anomaly （SSTA） in the equatorial central Pacific via surface warm advection. Subsequently, an atmospheric Rossby wave is stimulated to the northwest of the warm SSTA, which in turn enhances the at- mospheric dipole anomalies over the western Pacific. Therefore, the air-sea feedbacks involved tend to reinforce the effect of SHTP on the WPSH anomaly, and the role of SHTP on general circulation needs to be considered in a land-air-sea interaction framework.
文摘In this paper, a close relationship between the intraseasonal variation of subtropical high over East Asia and the convective activities around the South China Sea and the Philippines is analysed from OLR data.This relationship is studied by using the theory of wave propagating in a slowly varying medium and by using a quasi-geoslrophic, linear, spherical model and the IAP-GCM, respectively. The results show that when the SST is warming around the western tropical Pacific or the Philippines, the convective activities are intensified around the Philippines. As a consequence, the subtropical high will be intensified over East Asia. The computed results also show that when the anomaly of convective activities are caused around the Philippines, a teleconnection pattern of circulation anomalies will be caused over South Asia, East Asia and North America.
基金National Key Basic Research and Development Planning Program of China(Program 973)(2013CB430202)China Special Fund for Meteorological Research in the Public Interest(Major Projects)(GYHY201506001-1)National Natural Science Foundation of China(91337109,41305080)
文摘By adopting characteristic index data for the Western Pacific Subtropical High(WPSH) from the National Climate Center of China, U.S. National Centers for Environmental Prediction-National Center for Atmospheric Research(NCEP/NCAR) reanalysis data, and the National Oceanic and Atmospheric Administration(NOAA) sea surface temperature(SST) data, we studied the WPSH variability considering the background of climate warming by using a Gaussian filter, moving averages, correlation analysis, and synthetic analysis. Our results show that with climate warming over the past 60 years, significant changes in the WPSH include its enlarged area, strengthened intensity,westward extended ridge point and southward expanded southern boundary, as well as enhanced interannual fluctuations in all these indices. The western ridge point of the WPSH consistently varies with temperature changes in the Northern Hemisphere, but the location of the ridgeline varies independently. The intensity and area of the WPSH were both significantly increased in the late 1980 s. Specifically, the western ridge point started to significantly extend westward in the early 1990 s, and the associated interannual variability had a significant increase in the late 1990 s; in addition, the ridgeline was swaying along the north-south-north direction, and the corresponding variability was also greatly enhanced in the late 1990 s. With climate warming, the SST increase becomes more weakly correlated with the WPSH intensity enhancement but more strongly correlated with the westward extension of the ridge point in the equatorial central and eastern Pacific Ocean in winter, corresponding to an expanding WPSH in space. In the northern Pacific in winter, the SST decrease has a weaker correlation with the southerly location of the ridgeline but also a stronger correlation with the westward extension of the ridge point. In the tropical western Pacific in winter, the correlations of the SST decrease with the WPSH intensity enhancement, and the westward extension of the ridge point is strengthened. These observations can be explained by strengthened Hadley circulations, the dominant effects of the southward shift, and additional effects of the weakened ascending branch of the Walker circulation during warm climatological periods,which consequently lead to strengthened intensities, increased areas, and southward expansions of the WPSH in summer.
文摘A case is reported, during which the Subtropical High over the Western Pacific (hereafter, SHWP in abbreviation) shifted northwestward and met-yu at Chaniiang River valley ended. Several numerical experiments onSHWP activity influenced by the heating over south Asia monsoon area are carried out, and the statistic significance of the results is checked. The results indicate that the enhancement of positive heating over South Asia willmotivate a wave-like series of anomaly centers, which propagate northeastward from the maximum heating center.so that a strong positive potential height anomaly center will set up from North China to Japan at Day X resultingin the enhancement of SHWP. Comparison of the influence upon SHWP by the heating over south Asia monsoonarea with that over ITCZ area south to SHWP is also carried out. It is pointed out that the heating over South Asiamonsoon area tends to favor SHWP north\vard movement while the heating over ITCZ area tends to thvor SHWPwestward stretching. As for the time to begin to influence on SHWP, the heating over south Asia monsoon areafavors the enhancement of SHWP atter Day 3 while that over ITCZ south to SHWP effects atter Day 5.
基金This work was supported by the National Key Programme for Developing Basic Sciences (G1998040900-Part-1).
文摘Index series of Subtropical High over the western Pacific was extended to AD 1880 by using of statistical and modeling method. Reconstructed indices by both methods show good accordance each other. Association of the indices to the rainfall patterns over eastern China indicated the robustness of the reconstructions.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.41905055 and 41721004)the Natural Science Foundation of Jiangsu Province(Grant No.BK20190500)the Fundamental Research Funds for the Central Universities(Grant No.B200202145).
文摘It is well known that on the interannual timescale,the westward extension of the western North Pacific subtropical high(WNPSH)results in enhanced rainfall over the Yangtze River basin(YRB)in summer,and vice versa.This study identifies that this correspondence experiences a decadal change in the late 1970s.That is,the WNPSH significantly affects YRB precipitation(YRBP)after the late 1970s(P2)but not before the late 1970s(P1).It is found that enhanced interannual variability of the WNPSH favors its effect on YRB rainfall in P2.On the other hand,after removing the strong WNPSH cases in P2 and making the WNPSH variability equivalent to that in P1,the WNPSH can still significantly affect YRB rainfall,suggesting that the WNPSH variability is not the only factor that affects the WNPSH-YRBP relationship.Further results indicate that the change in basic state of thermal conditions in the tropical WNP provides a favorable background for the enhanced WNPSH-YRBP relationship.In P2,the lower-tropospheric atmosphere in the tropical WNP gets warmer and wetter,and thus the meridional gradient of climatological equivalent potential temperature over the YRB is enhanced.As a result,the WNPSH-related circulation anomalies can more effectively induce YRB rainfall anomalies through affecting the meridional gradient of equivalent potential temperature over the YRB.
基金Research on the Theory and Methods for the Diagnosis and Prediction of Flood-Inflicting Heavy Rains in Southern China (2004CB418304)a key national project for fundamental research program National Natural Science Foundation of China (40575045)
文摘The NCEP/NCAR II daily mean reanalysis data and observed precipitation data are employed to investigate the westward extension of the western Pacific subtropical high (WPSH) during the heavy rain period over the southern China in June 2005. Results show that there may exist a relationship between the east-west shift of the WPSH and the process of a southern China heavy rain. The analysis indicates that the vertical motion in the WPSH area is mainly caused by the latent heat release of monsoon rain belts on its northern and southern sides. The vertical motion could cause the accumulation of air mass in the center and west of the WPSH, which leads to its strengthening. The appearance of the northern and southern monsoon rain belts could not only enhance the WPSH by strengthening the descending draft, but also excite the development of positive vorticity and restrict the WPSH's movement in the north-south direction. Moreover, the Indian monsoon rainfall to the west of the WPSH may excite the development of anticyclonic vorticity on its eastern side, which leads to the westward extension of the WPSH.
文摘Numerical experiments are carried out using a global spectral model to study the role of an ideal heating source over the western tropical Pacific region in a medium-term weather process that marks the western advancement of the subtropical high in mid-June 1979. The result has indicated that the effect of the ideal heating source is evident in about 4 days after the inclusion in the high and the circulation at mid-and high-latitudes over the eastern part of China; the disturbance produced over the tropical ocean first transfers towards the northwest along the easterly flow on the southern edge of the subtropical high and then divides into two branches as it moves over the westerly over the mid-latitude area, one continuing the journey northwestward and the other turning to the northeast by east, resulting in changes in the subtropical high and the westerly through combined action.
文摘In this paper, using the daily grid data (2.5 × 2.5) of the ECMWF / WMO, we have computed respectively the three-dimensional wave activity flux in the stages of pre-onset, prevailing and post ending of Meiyu from 1 to 31 July 1982. The potential vorticity field is taken as the physical quantity relating the wave activity flux to the variation of the subtropical high over the Western Pacific. It is found that the three-dimensional wave activity flux is a powerful means for diagnosis of the variation of the subtropical high over the Western Pacific: The region of the subtropical high is just the confluence area of wave energy, whose changes in intensity and range decide the variation of the subtropical high. The confluence of wave energy comes from the monsoon flow in low latitudes, the Meiyu rain belts in middle latitudes and the heating fields on the eastern side of the Qinghai-Xizang Plateau. The relation between these sources and the subtropical high displays the self-adjusting mechanism among members of East-Asia summer monsoon.
基金supported by the National Natural Science Foundation of China(Grant No.41475039)the National Key Basic Research Program of China(Grant No.2015CB-953601)a China Postdoctoral Science Foundation-funded project(Grant No.2015M570500)
文摘The interdecadal variation of the summer western Pacific subtropical high(WPSH)during1948–2009 is investigated in this study.Compared with most previous works,which focused on the 500 h Pa geopotential height,the interdecadal variation of the horizontal winds,relative vorticity,and eddy geopotential height over the western Pacific are all analyzed.The weakened anticyclone and decreased negative relative vorticity at middle-low levels over the western Pacific suggest that the WPSH weakened during 1979–2009 relative to1948–78.After subtracting the zonal belt mean height between 0°and 40°N,the 500 hP a eddy geopotential height with significant negative anomalies over the western Pacific can correctly depict this weakened interdecadal variation of the WPSH.The illusory westward extension signal reflected by the 500 h Pa geopotential height may derive from the significant increment of the geopotential height at middle and lower latitudes in the late 1970s under global warming.
基金supported by the National Basic Research Program of China(Grant No.2010CB951901)the National Natural Science Foundation of China(Grant No.40821092)
文摘Based on the pentad mean ridgeline index of the western Pacific subtropical high (WPSH), the authors identified the two northward jumps of the WPSH from 1979 to 2008 and revealed their associations with the tropical SST anomalies. The authors show that the northward jumps, especially the second jump, exhibited remarkable interannual variability. In addition, the authors find that the two northward jumps were mutually independent and were influenced by the SST anomalies in the different regions of the tropical Pacific. The first jump was positively correlated with the SST anomalies in the tropical central Pacific from the preceding winter to June. In contrast, the second jump was positively related to ENSO in the preceding winter, but this correlation tended to weaken with the decay of ENSO and disappeared in July. Instead, a positive correlation was found in the Indian Ocean. We therefore suggest that ENSO plays an indirect role in the second jump through the capacitor effect of the Indian Ocean.
文摘By use of the filter analysis technique, the Complex Empirical Othogonal Function (CEOF) method and the ECMWF/WMO 2.5°×2.5°grid data of the geopotential heights during the summer months in 1988, an interseasonal process that the western Pacific subtropical high (WPSH) was anomalously far to the north in the first and second ten days of July is studied. It has been found that in the western Pacific subtropical region in the first and second ten days of July,it is the continuous assembly of low frequency geopotential waves (LFGWs) that leads to the abnormality of WPSH. This abnormality emerges with the enhancement of wave assembling and ceases while the wave assembling situation disappears. The structure of the low frequency assembling waves corresponds to the structure of subtropical high in its abnormal period. The effect of the assembling waves on the abnormality of subtropical high can be considered as the accumulation of disturbance energy carried by the low frequency waves from different directions in the western Pacific region.
基金Innovation Plans for Postgraduates of Higher Education Colleges in Jiangsu Province(E30000008098-3)Natural Science Foundation of China (40575045)+1 种基金National Key Fundamental ResearchDevelopment Plans (2004CB418302 2004CB418303)
文摘Using NCEP/NCAR daily reanalysis data and SCSMEX data, an investigation is carried out of the relationship between the position variation of the west Pacific subtropical high （WPSH） and the apparcnt heating in June 1998 based on the complete vertical vorticlty equation. It is tbund that the non-adiabatic heating plays an important role in the position variation of WPSH. In comparison with climatic mean status, the vertical change of non-adiabatic heating is stronger in the north side of WPSH in June 1998, but weaker in the south side of WPSH. The anomalous non-uniform heating induces anomalous cyclonic vorticity in South China, areas to lhe south of the Yangtze and its mid-lower valleys, but anomalous anticyclonic vorticity in the Indo-China Peninsula and South China Sea areas lead to the more southward position of WPSH than the mean.
基金Key Laboratory on Natural Disasters for Jiangsu Province (KLME050210)
文摘Comparisons of the west Pacific subtropical high with the South Asia High are made using the NCEP/NCAR and ECMWF 500 hPa and 100 hPa monthly boreal geopotential height fields for the period 1961-2000. Discrepancies are found for the time prior to 1980. The west Pacific subtropical high in the NCEP/NCAR data is less intense than in ECMWF data before 1980. The range and strength of the west Pacific subtropical high variation described by the NCEP/NCAR data are larger than those depicted by ECMWF data. The same situation appears in the 100-hPa geopotential field. These discoveries suggest that the interdecadal variation of the two systems as shown by the NCEP/NCAR data may not be true. Besides, the South Asia High center in the NCEP/NCAR data is obviously stronger than in the ECMWF data during the periods 1969, 1979-1991 and 1992-1995. Furthermore, the range is larger from 1992 to 1995.
基金Research on Floods-Causing Heavy Rains in the Valley of Huaihe River in 2003, a projectfrom the National Meteorological Center
文摘1 INTRODUCTION In summer, different assembly of the intensity, location and vertical structure of the subtropical high and the earlier/later time of its seasonal northwards jump bring about different precipitation patterns over China. Therefore, subtropical high activity and its cause during the occurrence of extreme climatic event over China and the cause of China drought/flood are studied to improve weather forecasting.
基金the National Natural Science Foundation of China(Grant Nos.41905055 and 41721004)the Natural Science Foundation of Jiangsu Province(Grant No.BK20190500)the Fundamental Research Funds for the Central Universities(Grant No.B200202145).
文摘This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high(WNPSH)and the East Asian westerly jet(EAJ)in summer on interannual timescales.The in-phase configuration of the WNPSH and EAJ is characterized by the westward(eastward)extension of the WNPSH and the southward(northward)shift of the EAJ,which is consistent with the general correspondence between their variations.The out-of-phase configuration includes the residual cases.We find that the in-phase configuration manifests itself as a typical meridional teleconnection.For instance,there is an anticyclonic(cyclonic)anomaly over the tropical western North Pacific and a cyclonic(anticyclonic)anomaly over the mid-latitudes of East Asia in the lower troposphere.These circulation anomalies are more conducive to rainfall anomalies over the Yangtze River basin and south Japan than are the individual WNPSH or EAJ.By contrast,for the out-of-phase configuration,the mid-latitude cyclonic(anticyclonic)anomaly is absent,and the lower-tropospheric circulation anomalies feature an anticyclonic(cyclonic)anomaly with a large meridional extension.Correspondingly,significant rainfall anomalies move northward to North China and the northern Korean Peninsula.Further results indicate that the out-of-phase configuration is associated with the developing phase of ENSO,with strong and significant sea surface temperature(SST)anomalies in the tropical central and eastern Pacific which occur simultaneously during summer and persist into the following winter.This is sharply different from the in-phase configuration,for which the tropical SSTs are not a necessity.
基金Chinese National Key Technology R&D Program (2009BAC51B01)National Basic Research Program "973" of China (2012CB417403)+1 种基金Meteorological Science Foundation of Jiangsu Province (KM201207)‘333’Project of Jiangsu Province and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘By using NCEP/NCAR daily reanalysis data and daily precipitation data of 740 stations in China, relationships between the position variation of the West Pacific subtropical high (WPSH) and the diabatic heating during persistent and intense rains in the Yangtze-Huaihe Rivers basin are studied. The results show that the position variation of WPSH is closely associated with the diabatic heating. There are strong apparent heating sources and moisture sinks in both the basin (to the north of WPSH) and the north of Bay of Bengal (to the west of WPSH) during persistent and intense rain events. In the basin, Q 1z begins to increase 3 days ahead of intense rainfall, maximizes 2 days later and then reduces gradually, but it changes little after precipitation ends, thus preventing the WPSH from moving northward. In the north of Bay of Bengal, 2 days ahead of strong rainfall over the basin, Q 1z starts to increase and peaks 1 day after the rain occurs, leading to the westward extension of WPSH. Afterwards, Q 1z begins declining and the WPSH makes its eastward retreat accordingly. Based on the complete vertical vorticity equation, in mid-troposphere, the vertical variation of heating in the basin is favorable to the increase of cyclonic vorticity north of WPSH, which counteracts the northward movement of WPSH and favors the persistence of rainbands over the basin. The vertical variation of heating in the north of Bay of Bengal is in favor of the increase of anti-cyclonic vorticity to the west of WPSH, which induces the westward extension of WPSH.
基金This study is supported by the Huaihe River Basin Energy and Water Cycle Experiment and Study Project under Grant No. 49794030 and East Asian Monsoon Experiment (EAMEX) under Grant No. 2001CCB00400.
文摘This paper explores the impact of the convective action over the low-latitude region, the water vapor transport around the West Pacific subtropical high (WPSH), and its convective action on the seasonal northward jump and southward withdrawal of the WPSH in summer by using the daily data set of NCEP and TBB for 1998. The research shows that in summer, the WPSH moves northward when the convection over the low-latitude tropical region intensifies and the subsidence region of the meridional vertically vertical circulation in meridional direction circulation over the region of 110?150癊 moves northward. Furthermore, as revealed by diagnostic analysis, the subtropical high moves northward after the obvious weakening of the longitudinal water vapor transport over the region around the subtropical high, but withdraws southward a pentad after the reduction of the latitudinal water vapor transport over the tropical West Pacific region. The research results show that the northward jump and southward withdrawal of the WPSH are closely related to the release of the convective latent heat at low latitudes and the water vapor transport at boundaries around WPSH and its convective action. The numerical simulation further validates the above-mentioned correlation between the variation of the action of the subtropical high and the preceding water vapor transport along with the convection characteristics.
文摘By using ECMWF (2. 5°×2. 5°) grid data, analyzing correlation for the summer (June-August) of 1980 (the West Pacific Subtropical High (WPSH) anomalously more to the south), 1988 (the WPSH anomalously more to the north), 1981 (normal) in the west Pacific area, distribution characteristics of the low frequency waves are discussed. The relationship between distribution of the low frequency waves and intraseasonal abnormality of the west subtropical high is also analyzed. There is some discussions:(1)If the WPSH acts anomalously in summer, there is a distinct zonal wave series in the subtropical zone of the north Pacific.(2) One of the important characteristics of the WPSH abnormality is that there are low frequency geopotential high centres from east Pacific and northeast Asia, being combined in the west Pacific area.For different circulation, the combination areas are different, which define the WSPH anomalously more to the north or south.
