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
Using the relative vorticity averaged over a certain area, a new index for measuring the longitudinal position of the subtropical high (SH) in the western Pacific is proposed to avoid the increasing trend of heights i...Using the relative vorticity averaged over a certain area, a new index for measuring the longitudinal position of the subtropical high (SH) in the western Pacific is proposed to avoid the increasing trend of heights in the previous indices based on geopotential height. The years of extreme westward and eastward extension of SH using the new index are in good agreement with those defined by height index. There exists a distinct difference in large-scale circulation between the eastward and westward extension of SH under the new definition, which includes not only the circulation in the middle latitudes but also the flow in the lower latitudes. It seems that when the SH extends far to the east (west), the summer monsoon in the South China Sea is stronger (weaker) and established earlier (later). In addition, there exists a good relationship between the longitudinal position of SH and the summer rainfall in China. A remarkable negative correlation area appears in the Changjiang River valley, indicating tha展开更多
Using the data of 500 hPa geopotential height from 1951 to 1995, SST roughly in the same period and OLR data from 1974 to 1994, the relation between the anomalies of subtropical high (STH for short) and the tropical c...Using the data of 500 hPa geopotential height from 1951 to 1995, SST roughly in the same period and OLR data from 1974 to 1994, the relation between the anomalies of subtropical high (STH for short) and the tropical circulations including the Asian monsoon as well as the convective activity are studied. In order to study the physical process of the air-sea interaction related to STH anomaly, the correlation of STH with SST at various sea areas, lagged and simultaneous, has been calculated. Comparing the difference of OLR, wind fields, vertical circulations and SST anomalies in the strong and weak STH, we investigate the characteristics of global circulations and the SST distributions related to the anomalous STH at the western Pacific both in winter and summer. Much attention has been paid to the study of the air-sea interaction and the relationship between the East Asian monsoon and the STH in the western Pacific. A special vertical circulation, related to the STH anomalies is found, which connects the monsoon current to the west and the vertical flow influenced by the SST anomaly in the tropical eastern Pacific.展开更多
Using the NCEP/NCAR reanalysis data, the China rainfall data of the China Meteorological Administration, and the sea surface temperature (SST) data of NOAA from 1951-2000, the features of the anomalous longitudinal po...Using the NCEP/NCAR reanalysis data, the China rainfall data of the China Meteorological Administration, and the sea surface temperature (SST) data of NOAA from 1951-2000, the features of the anomalous longitudinal position of the subtropical high in the western Pacific (SHWP) in the pre-rainy season in South China and associated circulation and precipitation are studied. Furthermore, the relationship between SHWP and SST and the eastern Asian winter monsoon is also investigated. Associated with the anomalous longitudinal position of SHWP in the pre-rainy season in South China, the flow patterns in both the middle and lower latitudes are different. The circulation anomalies greatly influence the precipitation in the pre-rainy season in South China. When the SHWP is in a west position (WP), the South China quasi-stationary front is stronger with more abundant precipitation there. However, when the SHWP is in an east position (EP), a weaker front appears with a shortage of precipitation there. There exists a good relationship between the longitudinal position of SHWP and SST in the tropical region. A negative correlation can be found both in the central and eastern tropical Pacific and the Indian Ocean. This means that the higher (lower) SST there corresponds to a west (east) position of SHWP. This close relationship can be found even in the preceding autumn and winter. A positive correlation appears in the western and northern Pacific and large correlation coefficient values also occur in the preceding autumn and winter. A stronger eastern Asian winter monsoon will give rise to cooler SSTs in the Kuroshio and the South China Sea regions and it corresponds to negative SST anomaly (SSTA) in the central and eastern Pacific and positive SSTA in the western Pacific in winter and the following spring. The whole tropical SSTA pattern, that is, positive (negative) SSTA in the central and eastern Pacific and negative (positive) SSTA in the western Pacific, is favorable to the WP (EP) of SHWP.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
Both 1981 and 2013 were weak La Nifia years with a similar sea surface temperature (SST) anomaly in the tropical Pacific, yet the westem Pacific subtropical high (WPSH) during August exhibited an opposite anomaly ...Both 1981 and 2013 were weak La Nifia years with a similar sea surface temperature (SST) anomaly in the tropical Pacific, yet the westem Pacific subtropical high (WPSH) during August exhibited an opposite anomaly in the two years. A comparison indicates that, in the absence of a strong SST anomaly in the tropics, the cold advection from Eurasian high latitudes and the convection of the western Pacific warm pool play important roles in influencing the strength and position of the WPSH in August. In August 1981, the spatial pattern of 500 hPa geopotential height was characterized by a meridional circulation with a strong ridge in the Ural Mountains and a deep trough in Siberia, which provided favorable conditions for cold air invading into the lower latitudes. Accordingly, the geopotential height to the north of the WPSH was reduced by the cold advection anomaly from high latitudes, resulting in an eastward retreat of the WPSH. Moreover, an anomalous cyclonic circulation in the subtropical western Pacific, excited by enhanced warm pool convection, also contributed to the eastward retreat of the WPSH. By contrast, the influence from high latitudes was relatively weak in August 2013 due to a zonal circulation pattern over Eurasia, and the anomalous anticyclonic circulation induced by suppressed warm pool convection also facilitated the westward extension of the WPSH. Therefore, the combined effects of the high latitude and tropical circulations may contribute a persistent anomaly of the WPSH in late summer, despite the tropical SST anomaly being weak.展开更多
Western North Pacific Subtropical High is a very important atmospheric circulation system influencing the summer climate over eastern China. Its interdecadal change is analyzed in this study. There is a significant de...Western North Pacific Subtropical High is a very important atmospheric circulation system influencing the summer climate over eastern China. Its interdecadal change is analyzed in this study. There is a significant decadal shift in about 1979/1980. Since 1980, the Western North Pacific Subtropical High has enlarged, intensified, and shifted southwestward. This change gives rise to an anti-cyclonic circulation anomaly over the region from the South China Sea to western Pacific and thus causes wet anomalies over the Yangtze River valley. During the summers of 1980-1999, the precipitation is 63.9 mm above normal, while during 1958-1979 it is 27.3 mm below normal. The difference is significant at the 99% confidence level as a t-test shown. The southwestward expanding of the Western North Pacific Subtropical High also leads to a significant warming in southern China, during 1980-1999 the summer mean temperature is 0.37篊 warmer than that of the period 1958-1979. The strong warming is primarily due to the clearer skies associated with the stronger downward air motion as the Western North Pacific Subtropical High expanding to the west and controlling southern China. It is also found that the relative percentage of tropical cyclones in the regions south of 20篘 is decreasing since the 1980s, but in the regions north of 20篘 that is increasing at the same time. The Western North Pacific Subtropical High responds significantly to sea surface temperature of the tropical eastern Pacific with a lag of one-two seasons and simultaneously to sea surface temperature of the tropical Indian Ocean. The changes in the sea surface temperatures are mainly responsible for the interdecadal variability of the Western North Pacific Subtropical High.展开更多
The anomalous behavior of the western Pacific subtropical high (WPSH) in E1 Nifio developing summer is studied based on the composite results of eight major E1 Nifio events during 1979-2013. It is shown that the WPS...The anomalous behavior of the western Pacific subtropical high (WPSH) in E1 Nifio developing summer is studied based on the composite results of eight major E1 Nifio events during 1979-2013. It is shown that the WPSH tends to retreat eastwards with weak intensity during the developing summer. The anomaly exhibits an intraseasonal variation with a weaker anomaly in June and July and a stronger anomaly in August, indicating that different underlying physical mechanisms may be responsible for the anomalous WPSH during early and late summer periods. In June and July, owing to the cold advection anomaly characterized as a weak northerly anomaly from high latitudes, geopotential height in East Asia is reduced and the WPSH tends to retreat eastwards slightly. By contrast, enhanced convection over the warm pool in August makes the atmosphere more sensitive to E1 Nifio forcing. Consequently, a cyclonic anomaly in the western Pacific is induced, which is consistent with the seasonal march of atmospheric circulation from July to August. Accordingly, geopotential height in the western Pacific is reduced significantly, and the WPSH tends to retreat eastwards remarkably in August. Different from the developing summer, geopotential height in the decaying summer over East Asia and the western Pacific tends to enhance and extend northwards from June to August consistently, reaching the maximum anomaly in August. Therefore, the seasonal march plays an important role in the WPSH anomaly for both the developing and decaying summer.展开更多
By using the numerical and dynamical methods, the influence and restriction of the heat source forcing on the subtropical geopotential fields and flow fields are studied and discussed in a model atmosphere. The main r...By using the numerical and dynamical methods, the influence and restriction of the heat source forcing on the subtropical geopotential fields and flow fields are studied and discussed in a model atmosphere. The main results show that the zonal symmetrical solar radiation heating chief-ly induces the geopotential field changing gradually and leads the subtropical high moving slowly, but when the zonal asymmetric thermal difference between ocean and continent achieves its critical value, which usually causes the geopotential field a catastrophe, and consequently induces the subtropical high shake-up or jump. The abnormal activity of the subtropical high is possibly caused by the abnormality of the thermal factor. Key words Subtropical high - Thermal forcing Supported by National Natural Science Foundation (No. 49975012) and National ’ 973’ Key Program (No. G1998040907).展开更多
An intercomparison of summertime (JJA)subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously l...An intercomparison of summertime (JJA)subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously lower than the ERA-40 in the mid-to-lower troposphere in most regions of East Eurasia before the mid-1970s, but becomes higher than the ERA-40 after the mid-1970s and thus demonstrates stronger increased trends during the period of 1958-2001. Both reanalyses are lower than the observations in most regions of China. The NCEP/NCAR especially shows tremendously systematic lower values before the mid-1960s and displays abrupt changes before the 1970s. Several indices of the western North Pacific subtropical high (WNPSH), calculated from both reanalyzed summer geopotential heights, also reveal that the variation trend of the NCEP/NCAR is stronger than that of the ERA-40 in the mid-to-lower troposphere from 1958 to 2001. Through singular value decomposition (SVD) analysis, the summer geopotential heights at 500 hPa from the ERA-40 are better than the NCEP/NCAR counterparts at interacting with the precipitation over the East Asian monsoon region. The results indicate that the NCEP/NCAR in the mid-and-lower troposphere may overestimate interdecadal changes and should be used cautiously to study the relationship between the WNPSH and precipitation ove ther East Asia Monsoon region before the mid-1970s.展开更多
Using the intensity data of each northern subtropical high measured by monthly 500 hPa height charts for the recent 38 years (1954-1991), we calculate their correlations with the monthly sunspot number and monthly sol...Using the intensity data of each northern subtropical high measured by monthly 500 hPa height charts for the recent 38 years (1954-1991), we calculate their correlations with the monthly sunspot number and monthly solar radio flux at 10.7 cm wave length, respectively. Through strict test, we further confirm a series of high correlations. Next, using a method called the non-integer (year) wave, the significant response of each subtropical high's intensity to solar activity at its main period of 10.9-year length is found. Special attention is paid to that of the eastern Pacific high, the possible mechanism of such sensible response is also analysed.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
[Objective] The research aimed to study the reason of local heavy rainstorm forecast error in the subtropical high control. [Method] Started from summarizing the reason of forecast error, by using the conventional gro...[Objective] The research aimed to study the reason of local heavy rainstorm forecast error in the subtropical high control. [Method] Started from summarizing the reason of forecast error, by using the conventional ground observation data, the upper air sounding data, T639, T213 and European Center (ECMWF) numerical prediction product data, GFS precipitation forecast product of U.S. National Center for Environmental Prediction, the weather situation, physical quantity field in a heavy rainstorm process which happened in the north of Shaoyang at night on August 5, 2010 were fully analyzed. Based on the numerical analysis forecast product data, the reason of heavy rainstorm forecast error in the subtropical high was comprehensively analyzed by using the comparison and analysis method of forecast and actual situation. [Result] The forecasters didn’t deeply and carefully analyze the weather situation. On the surface, 500 hPa was controlled by the subtropical high, but there was the weak shear line in 700 and 850 hPa. Moreover, they neglected the influences of weak cold air and easterlies wave. The subtropical high quickly weakened, and the system adjustment was too quick. The wind field variations in 850, 700 and 500 hPa which were forecasted by ECMWF had the big error with the actual situation. It was by east about 2 longitudes than the actual situation. In summer forecast, they only considered the intensity and position variations of 500 hPa subtropical high, and neglected the situation variations in the middle, low levels and on the ground. It was the most key element which caused the rainstorm forecast error in the subtropical high. The forecast error of numerical forecast products on the height field situation variation was big. The precipitation forecasts of Japan FSAS, U.S. National Center for Environmental Prediction GFS, T639 and T213 were all small. The humidity field forecast value of T639 was small. In the rainstorm forecast, the local rainstorm forecast index and method weren’t used in the forecast practice. In the precipitation forecast process, they only paid attention to the score prediction of station and didn’t value the non-site prediction. Some important physical quantity factors weren’t carefully studied. [Conclusion] The research provided the reference basis for the forecast and early warning of local heavy rainstorm.展开更多
The cloud variations under subtropical high(STH) conditions during summers over a ten-year period are studied using combined data from the International Satellite Cloud Climatology Project and the National Centers for...The cloud variations under subtropical high(STH) conditions during summers over a ten-year period are studied using combined data from the International Satellite Cloud Climatology Project and the National Centers for Environmental Prediction.The results reveal that clouds mainly experience an isolated evolution in the STHs,which is designated in this study by the 1540 gpm geopotential lines at 850 hPa.In the STH domain throughout the Northern Hemisphere,the average amount of total clouds exceeds 30%.Low clouds dominate in the STH domain,contributing over 60%of total cloud amount within the Pacific subtropical high and over 40%within the Atlantic subtropical high.The prevalence of low clouds in above regions is determined by the circulation pattern around 150°-180°E and 850 hPa,which suppresses both the upward development of the cloud tops and the water vapor divergences near the surface.Furthermore,clouds present great geographical incoherence within the STH domain.In the eastern STHs,the amount of middle and low clouds increases to peak in the early morning and decreases to a trough in the afternoon,while the amount of high clouds remains stable throughout the day.Conversely,in the western STHs,the diurnal amplitude of low and middle clouds is less than three,while high clouds dramatically reach the maximum in the afternoon and drop to the minimum in the evening.Among the nine cloud categories,stratocumulus clouds with greater optical thickness account for the most under STH conditions,no matter their occurrence or amount,causing more shortwave cloud radiative forcing to cool the local atmosphere and surface as a consequence.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
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
To analyze the dynamic mechanism of unusual activities of the subtropical high, the space-time varible separation of the partial differential vortex equations is carried out with Galerkin methods based on the heat for...To analyze the dynamic mechanism of unusual activities of the subtropical high, the space-time varible separation of the partial differential vortex equations is carried out with Galerkin methods based on the heat force and the whirl movement dissipation effect. Aiming at the subjective and man-made conventional method of choice in the space basis functions, we propose to combine the empirical orthogonal function (EOF) analysis with the genetic algorithm to inverse the space basis functions from the actual sequence of fields. A group of trigonometric functions are chosen as a generalized space basis function. With the least-squares error of the basis function and EOF typical fields, and with the complete orthogonality of basis functions, we can get the dual-bound function. A genetic algorithm is then introduced to carry out surface fitting and coefficient optimization of the basis function. As a result, the objective and reasonable constant differential equation of the subtropical high is obtained by inversion. Finally, based on the obtained nonlinear dynamics model, the dynamic behavior and mechanism of the subtropical high is analyzed and discussed under the influence of heat force. We find that solar radiation and zonal differences in land and sea are important factors impacting the potential field and flow field changes of the subtropical areas. These factors lead to strength changes of the subtropical high and medium-term advance/retreat activities. The former is a gradual change, while the latter shows more break characteristics. Meaningful results are obtained in the analysis.展开更多
On Page 119 of the printed edition (Issue 1, Vol. 26), the paper title should be "Intercomparison of the Summertime Subtropical High from the ERA-40 and NCEP/NCAR Reanalysis over East Eurasia and the Western North ...On Page 119 of the printed edition (Issue 1, Vol. 26), the paper title should be "Intercomparison of the Summertime Subtropical High from the ERA-40 and NCEP/NCAR Reanalysis over East Eurasia and the Western North Pacific". The editorial office and the authors are sincerely sorry for any inconvenience this may have caused.展开更多
Aiming at the difficulty of accurately constructing the dynamic model of subtropical high, based on the potential height field time series over 500 hPa layer of T106 numerical forecast products, by using EOF(empirica...Aiming at the difficulty of accurately constructing the dynamic model of subtropical high, based on the potential height field time series over 500 hPa layer of T106 numerical forecast products, by using EOF(empirical orthogonal function) temporal-spatial separation technique, the disassembled EOF time coefficients series were regarded as dynamical model variables, and dynamic system retrieval idea as well as genetic algorithm were introduced to make dynamical model parameters optimization search, then, a reasonable non-linear dynamic model of EOF time-coefficients was established. By dynamic model integral and EOF temporal-spatial components assembly, a mid-/long-term forecast of subtropical high was carried out. The experimental results show that the forecast results of dynamic model are superior to that of general numerical model forecast results. A new modeling idea and forecast technique is presented for diagnosing and forecasting such complicated weathers as subtropical high.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 by the Innovation Key Prograrn of the Chinese Academy of Sciences ZKCX2-SW-210the National Natural Science Foundation of China under Grant Nol40135020,and 40233033.
文摘Using the relative vorticity averaged over a certain area, a new index for measuring the longitudinal position of the subtropical high (SH) in the western Pacific is proposed to avoid the increasing trend of heights in the previous indices based on geopotential height. The years of extreme westward and eastward extension of SH using the new index are in good agreement with those defined by height index. There exists a distinct difference in large-scale circulation between the eastward and westward extension of SH under the new definition, which includes not only the circulation in the middle latitudes but also the flow in the lower latitudes. It seems that when the SH extends far to the east (west), the summer monsoon in the South China Sea is stronger (weaker) and established earlier (later). In addition, there exists a good relationship between the longitudinal position of SH and the summer rainfall in China. A remarkable negative correlation area appears in the Changjiang River valley, indicating tha
文摘Using the data of 500 hPa geopotential height from 1951 to 1995, SST roughly in the same period and OLR data from 1974 to 1994, the relation between the anomalies of subtropical high (STH for short) and the tropical circulations including the Asian monsoon as well as the convective activity are studied. In order to study the physical process of the air-sea interaction related to STH anomaly, the correlation of STH with SST at various sea areas, lagged and simultaneous, has been calculated. Comparing the difference of OLR, wind fields, vertical circulations and SST anomalies in the strong and weak STH, we investigate the characteristics of global circulations and the SST distributions related to the anomalous STH at the western Pacific both in winter and summer. Much attention has been paid to the study of the air-sea interaction and the relationship between the East Asian monsoon and the STH in the western Pacific. A special vertical circulation, related to the STH anomalies is found, which connects the monsoon current to the west and the vertical flow influenced by the SST anomaly in the tropical eastern Pacific.
基金This work was supported by the National Key Basic Research and Development Project of China 2004CB18300the Key Knowledge Innovation Project of Chinese Academy of Sciences(Grand No.KZCX3-SW-226)the National Natural Science Foundation of China under Grant Nos.40135020 and 40325015.
文摘Using the NCEP/NCAR reanalysis data, the China rainfall data of the China Meteorological Administration, and the sea surface temperature (SST) data of NOAA from 1951-2000, the features of the anomalous longitudinal position of the subtropical high in the western Pacific (SHWP) in the pre-rainy season in South China and associated circulation and precipitation are studied. Furthermore, the relationship between SHWP and SST and the eastern Asian winter monsoon is also investigated. Associated with the anomalous longitudinal position of SHWP in the pre-rainy season in South China, the flow patterns in both the middle and lower latitudes are different. The circulation anomalies greatly influence the precipitation in the pre-rainy season in South China. When the SHWP is in a west position (WP), the South China quasi-stationary front is stronger with more abundant precipitation there. However, when the SHWP is in an east position (EP), a weaker front appears with a shortage of precipitation there. There exists a good relationship between the longitudinal position of SHWP and SST in the tropical region. A negative correlation can be found both in the central and eastern tropical Pacific and the Indian Ocean. This means that the higher (lower) SST there corresponds to a west (east) position of SHWP. This close relationship can be found even in the preceding autumn and winter. A positive correlation appears in the western and northern Pacific and large correlation coefficient values also occur in the preceding autumn and winter. A stronger eastern Asian winter monsoon will give rise to cooler SSTs in the Kuroshio and the South China Sea regions and it corresponds to negative SST anomaly (SSTA) in the central and eastern Pacific and positive SSTA in the western Pacific in winter and the following spring. The whole tropical SSTA pattern, that is, positive (negative) SSTA in the central and eastern Pacific and negative (positive) SSTA in the western Pacific, is favorable to the WP (EP) of SHWP.
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supported by the National Science Foundation of China(Grant Nos.41475052 and 41405058)
文摘Both 1981 and 2013 were weak La Nifia years with a similar sea surface temperature (SST) anomaly in the tropical Pacific, yet the westem Pacific subtropical high (WPSH) during August exhibited an opposite anomaly in the two years. A comparison indicates that, in the absence of a strong SST anomaly in the tropics, the cold advection from Eurasian high latitudes and the convection of the western Pacific warm pool play important roles in influencing the strength and position of the WPSH in August. In August 1981, the spatial pattern of 500 hPa geopotential height was characterized by a meridional circulation with a strong ridge in the Ural Mountains and a deep trough in Siberia, which provided favorable conditions for cold air invading into the lower latitudes. Accordingly, the geopotential height to the north of the WPSH was reduced by the cold advection anomaly from high latitudes, resulting in an eastward retreat of the WPSH. Moreover, an anomalous cyclonic circulation in the subtropical western Pacific, excited by enhanced warm pool convection, also contributed to the eastward retreat of the WPSH. By contrast, the influence from high latitudes was relatively weak in August 2013 due to a zonal circulation pattern over Eurasia, and the anomalous anticyclonic circulation induced by suppressed warm pool convection also facilitated the westward extension of the WPSH. Therefore, the combined effects of the high latitude and tropical circulations may contribute a persistent anomaly of the WPSH in late summer, despite the tropical SST anomaly being weak.
基金National Developing Program for Basic Sciences No.1998040900National Natural Science Foundation of China No. 40105007
文摘Western North Pacific Subtropical High is a very important atmospheric circulation system influencing the summer climate over eastern China. Its interdecadal change is analyzed in this study. There is a significant decadal shift in about 1979/1980. Since 1980, the Western North Pacific Subtropical High has enlarged, intensified, and shifted southwestward. This change gives rise to an anti-cyclonic circulation anomaly over the region from the South China Sea to western Pacific and thus causes wet anomalies over the Yangtze River valley. During the summers of 1980-1999, the precipitation is 63.9 mm above normal, while during 1958-1979 it is 27.3 mm below normal. The difference is significant at the 99% confidence level as a t-test shown. The southwestward expanding of the Western North Pacific Subtropical High also leads to a significant warming in southern China, during 1980-1999 the summer mean temperature is 0.37篊 warmer than that of the period 1958-1979. The strong warming is primarily due to the clearer skies associated with the stronger downward air motion as the Western North Pacific Subtropical High expanding to the west and controlling southern China. It is also found that the relative percentage of tropical cyclones in the regions south of 20篘 is decreasing since the 1980s, but in the regions north of 20篘 that is increasing at the same time. The Western North Pacific Subtropical High responds significantly to sea surface temperature of the tropical eastern Pacific with a lag of one-two seasons and simultaneously to sea surface temperature of the tropical Indian Ocean. The changes in the sea surface temperatures are mainly responsible for the interdecadal variability of the Western North Pacific Subtropical High.
基金supported by the National Science Foundation of China (Grant Nos. 41475052 and 41630530)
文摘The anomalous behavior of the western Pacific subtropical high (WPSH) in E1 Nifio developing summer is studied based on the composite results of eight major E1 Nifio events during 1979-2013. It is shown that the WPSH tends to retreat eastwards with weak intensity during the developing summer. The anomaly exhibits an intraseasonal variation with a weaker anomaly in June and July and a stronger anomaly in August, indicating that different underlying physical mechanisms may be responsible for the anomalous WPSH during early and late summer periods. In June and July, owing to the cold advection anomaly characterized as a weak northerly anomaly from high latitudes, geopotential height in East Asia is reduced and the WPSH tends to retreat eastwards slightly. By contrast, enhanced convection over the warm pool in August makes the atmosphere more sensitive to E1 Nifio forcing. Consequently, a cyclonic anomaly in the western Pacific is induced, which is consistent with the seasonal march of atmospheric circulation from July to August. Accordingly, geopotential height in the western Pacific is reduced significantly, and the WPSH tends to retreat eastwards remarkably in August. Different from the developing summer, geopotential height in the decaying summer over East Asia and the western Pacific tends to enhance and extend northwards from June to August consistently, reaching the maximum anomaly in August. Therefore, the seasonal march plays an important role in the WPSH anomaly for both the developing and decaying summer.
文摘By using the numerical and dynamical methods, the influence and restriction of the heat source forcing on the subtropical geopotential fields and flow fields are studied and discussed in a model atmosphere. The main results show that the zonal symmetrical solar radiation heating chief-ly induces the geopotential field changing gradually and leads the subtropical high moving slowly, but when the zonal asymmetric thermal difference between ocean and continent achieves its critical value, which usually causes the geopotential field a catastrophe, and consequently induces the subtropical high shake-up or jump. The abnormal activity of the subtropical high is possibly caused by the abnormality of the thermal factor. Key words Subtropical high - Thermal forcing Supported by National Natural Science Foundation (No. 49975012) and National ’ 973’ Key Program (No. G1998040907).
基金supported by the National Key Basic Research Program of China (Grant No. 2006CB400502 and 2009CB723904)the National Natural Science Foundation of China (Grant No.40805032)IAP/CAS Knowledge Innovation Project(IAP07405)
文摘An intercomparison of summertime (JJA)subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously lower than the ERA-40 in the mid-to-lower troposphere in most regions of East Eurasia before the mid-1970s, but becomes higher than the ERA-40 after the mid-1970s and thus demonstrates stronger increased trends during the period of 1958-2001. Both reanalyses are lower than the observations in most regions of China. The NCEP/NCAR especially shows tremendously systematic lower values before the mid-1960s and displays abrupt changes before the 1970s. Several indices of the western North Pacific subtropical high (WNPSH), calculated from both reanalyzed summer geopotential heights, also reveal that the variation trend of the NCEP/NCAR is stronger than that of the ERA-40 in the mid-to-lower troposphere from 1958 to 2001. Through singular value decomposition (SVD) analysis, the summer geopotential heights at 500 hPa from the ERA-40 are better than the NCEP/NCAR counterparts at interacting with the precipitation over the East Asian monsoon region. The results indicate that the NCEP/NCAR in the mid-and-lower troposphere may overestimate interdecadal changes and should be used cautiously to study the relationship between the WNPSH and precipitation ove ther East Asia Monsoon region before the mid-1970s.
文摘Using the intensity data of each northern subtropical high measured by monthly 500 hPa height charts for the recent 38 years (1954-1991), we calculate their correlations with the monthly sunspot number and monthly solar radio flux at 10.7 cm wave length, respectively. Through strict test, we further confirm a series of high correlations. Next, using a method called the non-integer (year) wave, the significant response of each subtropical high's intensity to solar activity at its main period of 10.9-year length is found. Special attention is paid to that of the eastern Pacific high, the possible mechanism of such sensible response is also analysed.
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.
文摘[Objective] The research aimed to study the reason of local heavy rainstorm forecast error in the subtropical high control. [Method] Started from summarizing the reason of forecast error, by using the conventional ground observation data, the upper air sounding data, T639, T213 and European Center (ECMWF) numerical prediction product data, GFS precipitation forecast product of U.S. National Center for Environmental Prediction, the weather situation, physical quantity field in a heavy rainstorm process which happened in the north of Shaoyang at night on August 5, 2010 were fully analyzed. Based on the numerical analysis forecast product data, the reason of heavy rainstorm forecast error in the subtropical high was comprehensively analyzed by using the comparison and analysis method of forecast and actual situation. [Result] The forecasters didn’t deeply and carefully analyze the weather situation. On the surface, 500 hPa was controlled by the subtropical high, but there was the weak shear line in 700 and 850 hPa. Moreover, they neglected the influences of weak cold air and easterlies wave. The subtropical high quickly weakened, and the system adjustment was too quick. The wind field variations in 850, 700 and 500 hPa which were forecasted by ECMWF had the big error with the actual situation. It was by east about 2 longitudes than the actual situation. In summer forecast, they only considered the intensity and position variations of 500 hPa subtropical high, and neglected the situation variations in the middle, low levels and on the ground. It was the most key element which caused the rainstorm forecast error in the subtropical high. The forecast error of numerical forecast products on the height field situation variation was big. The precipitation forecasts of Japan FSAS, U.S. National Center for Environmental Prediction GFS, T639 and T213 were all small. The humidity field forecast value of T639 was small. In the rainstorm forecast, the local rainstorm forecast index and method weren’t used in the forecast practice. In the precipitation forecast process, they only paid attention to the score prediction of station and didn’t value the non-site prediction. Some important physical quantity factors weren’t carefully studied. [Conclusion] The research provided the reference basis for the forecast and early warning of local heavy rainstorm.
基金supported by the Special Funds for Public Welfare of China(Grant No.GYHY-QX-2007)the National Natural Science Foundation of China(Grant Nos.40730950,40675027,and 40805007).
文摘The cloud variations under subtropical high(STH) conditions during summers over a ten-year period are studied using combined data from the International Satellite Cloud Climatology Project and the National Centers for Environmental Prediction.The results reveal that clouds mainly experience an isolated evolution in the STHs,which is designated in this study by the 1540 gpm geopotential lines at 850 hPa.In the STH domain throughout the Northern Hemisphere,the average amount of total clouds exceeds 30%.Low clouds dominate in the STH domain,contributing over 60%of total cloud amount within the Pacific subtropical high and over 40%within the Atlantic subtropical high.The prevalence of low clouds in above regions is determined by the circulation pattern around 150°-180°E and 850 hPa,which suppresses both the upward development of the cloud tops and the water vapor divergences near the surface.Furthermore,clouds present great geographical incoherence within the STH domain.In the eastern STHs,the amount of middle and low clouds increases to peak in the early morning and decreases to a trough in the afternoon,while the amount of high clouds remains stable throughout the day.Conversely,in the western STHs,the diurnal amplitude of low and middle clouds is less than three,while high clouds dramatically reach the maximum in the afternoon and drop to the minimum in the evening.Among the nine cloud categories,stratocumulus clouds with greater optical thickness account for the most under STH conditions,no matter their occurrence or amount,causing more shortwave cloud radiative forcing to cool the local atmosphere and surface as a consequence.
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supported by the Joint Plan to Subsidize Innovative Young Scholars of the Chinese Academy of Sciences (No. IAP09305)
文摘To analyze the dynamic mechanism of unusual activities of the subtropical high, the space-time varible separation of the partial differential vortex equations is carried out with Galerkin methods based on the heat force and the whirl movement dissipation effect. Aiming at the subjective and man-made conventional method of choice in the space basis functions, we propose to combine the empirical orthogonal function (EOF) analysis with the genetic algorithm to inverse the space basis functions from the actual sequence of fields. A group of trigonometric functions are chosen as a generalized space basis function. With the least-squares error of the basis function and EOF typical fields, and with the complete orthogonality of basis functions, we can get the dual-bound function. A genetic algorithm is then introduced to carry out surface fitting and coefficient optimization of the basis function. As a result, the objective and reasonable constant differential equation of the subtropical high is obtained by inversion. Finally, based on the obtained nonlinear dynamics model, the dynamic behavior and mechanism of the subtropical high is analyzed and discussed under the influence of heat force. We find that solar radiation and zonal differences in land and sea are important factors impacting the potential field and flow field changes of the subtropical areas. These factors lead to strength changes of the subtropical high and medium-term advance/retreat activities. The former is a gradual change, while the latter shows more break characteristics. Meaningful results are obtained in the analysis.
文摘On Page 119 of the printed edition (Issue 1, Vol. 26), the paper title should be "Intercomparison of the Summertime Subtropical High from the ERA-40 and NCEP/NCAR Reanalysis over East Eurasia and the Western North Pacific". The editorial office and the authors are sincerely sorry for any inconvenience this may have caused.
基金Project supported by the National Natural Science Foundation of China (No.40375019) the Tropical Marine and Meteorology Science Foundation (No.200609) the Jiangsu Key Laboratory of Meteorological Disaster Foundation (No.KLME0507)
文摘Aiming at the difficulty of accurately constructing the dynamic model of subtropical high, based on the potential height field time series over 500 hPa layer of T106 numerical forecast products, by using EOF(empirical orthogonal function) temporal-spatial separation technique, the disassembled EOF time coefficients series were regarded as dynamical model variables, and dynamic system retrieval idea as well as genetic algorithm were introduced to make dynamical model parameters optimization search, then, a reasonable non-linear dynamic model of EOF time-coefficients was established. By dynamic model integral and EOF temporal-spatial components assembly, a mid-/long-term forecast of subtropical high was carried out. The experimental results show that the forecast results of dynamic model are superior to that of general numerical model forecast results. A new modeling idea and forecast technique is presented for diagnosing and forecasting such complicated weathers as subtropical high.