The long-term relationship between the tree-ring-reconstructed annual precipitation in northeastern Mongolia （PRM） and the Northern Hemisphere Zonal Circulation （NHZC）, defined as the normalized zonal mean sea-lev...The long-term relationship between the tree-ring-reconstructed annual precipitation in northeastern Mongolia （PRM） and the Northern Hemisphere Zonal Circulation （NHZC）, defined as the normalized zonal mean sea-level pressure at 60°N in May-June-July, is examined in this study. A significant correlation coefficient （0.31） was found between the NHZC indices and PRM based on the dataset for the period of 1872-1995. The mechanisms responsible for the relationship are discussed through analyses of the atmospheric general circulation variability associated with NHZC. It follows that NHZC-related atmospheric circulation variability provides an anomalous southeast flow from the ocean to Northeast Mongolia （northwest flow from Northeast Mongolia to the ocean） in the middle and low troposphere in positive （negative） phase of NHZC, resulting in more （less） water vapor transport to the target region and more （less） precipitation in Northeast Mongolia.展开更多
To infer the internal equilibrium structure of a gaseous planet, especially the equation of state(EOS) and size of its inner core,requires accurate determination of lower-order zonal gravitational coefficients. Modeli...To infer the internal equilibrium structure of a gaseous planet, especially the equation of state(EOS) and size of its inner core,requires accurate determination of lower-order zonal gravitational coefficients. Modeling of the gravitational signature associated with deep zonal circulation depends critically upon reliable subtraction of the dynamical components from totally derived gravitational coefficients. In the era of the Juno mission and the Grand Finale phase of the Cassini mission, it is timely and necessary to revisit and examine the so-called ‘Thermal Wind Equation(TWE)’, which has been extensively utilized to diagnose the dynamical parts of the gravitational fields measured by the two spacecrafts. TWE treats as negligible a few terms in the full equation of balance. However, the self-gravitational anomaly of the distorted fluid, unlike oblateness effects of solid-body rotation, is not a priori minor and thus should not be neglected in the name of approximation. Another equation, the ‘Thermal Gravitational Wind Equation(TGWE)’, includes this important additional term;we compare it with the TWE and show that physically the TGWE models a fundamentally different balance from the TWE and delivers numerical results considerably different from models based on the TWE. We conclude that the TWE balance cannot be relied upon to produce realistic convection models. Only after the TGWE balance is obtained can the relative importance of terms be assessed.The calculations we report here are based on two types of zonal circulations that are produced by realistically possible convections inside planets, instead of being constructed or assumed.展开更多
The present work is intended to simulate, in a rotating annulus of stratified liquid, the me-chanical effect of the Xizang (Tibetan) Plateau on the zonal circulation. The main featuresof three flow patterns around the...The present work is intended to simulate, in a rotating annulus of stratified liquid, the me-chanical effect of the Xizang (Tibetan) Plateau on the zonal circulation. The main featuresof three flow patterns around the plateau for different Rossby number R and rotating Eulernumber E are analysed. and a division diagram of the flow pattern in (R, E) plane is given.It has been found that under the condition that similarity criterions R and E of the experimentalfluid are the same as those existing in the atmosphere for monthly mean states in spring, au-tumn and winter months, the experimental results are satisfied for the following weathersystems over the plateau and its vicinities: the low vortex, trough and shear line over thesoutheast part of the plateau, the tilted ridge over the northwest part of the plateau, the troughpatterns over the upstream and dewnstream of the plateau, the vertical circulation structure, thejets on both north and southeast sides of the plateau, and so on. This shows that the mechanicaleffect of the Tibetan Plateau on the general circulation over East Asia deserves close atten-tion.展开更多
Zonal overturning circulation （ZOC） and its associated zonal heat flux （ZHF） are important components of the oceanic circulation and climate system, although these conceptions have not received adequate attentions...Zonal overturning circulation （ZOC） and its associated zonal heat flux （ZHF） are important components of the oceanic circulation and climate system, although these conceptions have not received adequate attentions. Heaving induced by inter-annual and decadal wind stress perturbations can give rise to anomalous ZOC and ZHF. Based on a simple reduced gravity model, the anomalous ZOC and ZHF induced by idealized heaving modes in the world oceans are studied. For example, in a Pacific-like model basin intensified equatorial easterly on decadal time scales can lead to a negative ZOC with a non-negligible magnitude （-0.3×10^6 m^3/s） and a considerable westward ZHF with an amplitude of -11.2 TW. Thus, anomalous ZOC and ZHF may consist of a major part of climate signals on decadal time scales and thus play an important role in the oceanic circulation and climate change.展开更多
This study reveals a significant positive connection between autumn non-tropical-cyclone heavy rainfall on Hainan Island and the intensity of Eastern Pacific(EP)El Ni?o events.That is,the amount of rainfall in super E...This study reveals a significant positive connection between autumn non-tropical-cyclone heavy rainfall on Hainan Island and the intensity of Eastern Pacific(EP)El Ni?o events.That is,the amount of rainfall in super EP El Ni?o years is more than that in normal EP El Ni?o years.Comparing EP El Ni?o years of different intensities,the cooler sea surface temperature in the northwestern Pacific during super EP El Ni?o years stimulates a negative surface latent heat flux(LHF)anomaly and abnormal anticyclonic circulation at 850 hPa.Under these conditions,an abnormal zonal vertical circulation develops in the northern South China Sea once a positive LHF anomaly and abnormal cyclonic circulation(ACC)at 850hPa occur in the Beibu Gulf.The abnormal zonal vertical circulation further strengthens the ascending motion over Hainan Island,as the critical factor that leads to excessive rainfall.Further analysis shows that the positive LHF anomaly,which can be attributed to the increased latent heat transfer which resulted from the increased surface wind speed,is an important trigger for the ACC.However,the ACC is also the supplier of favorable moisture conditions because it intensifies vapor convergence over Hainan Island and meridionally transports moisture from the South China Sea to northeastern Hainan Island,thereby generating heavy rainfall.This paper emphasizes that the impact of El Ni?o events,especially super El Ni?o events,on rainfall over Hainan Island cannot be ignored,even if the traditional view is that frequent rainfall occurs mainly in La Ni?a years.展开更多
The paper investigates the vertical circulation structure of the western Pacific subtropical high (STH) and its interannual variation features in relation tO East Asian subtropical summer monsoon and external thermal ...The paper investigates the vertical circulation structure of the western Pacific subtropical high (STH) and its interannual variation features in relation tO East Asian subtropical summer monsoon and external thermal forcing by using the high-resolution and good-quality observations from the 1998 South China Sea Summer Monsoon Experiment (SCSMEX), the NCEP 40-year reanalysis data and relevant SST and the STH parameters. It is found that the vertical circulation structures differ greatly in features between quasi-Stationary and transient components of the western Pacific STH. When rainstorms happen in the rainband of East Asian subtropical monsoon on the STH north side, the downdrafts are distinct around the ridge at a related meridian. The sinking at high (low) levels comes from the north (south) side of the STH, thereby revealing that the high is a tie between tropical and extratropical systems. The analyses of this paper suggest that the latent heat release associated with subtropical monsoon precipitation, the offshore SST and East Asian land-sea thermal contrast have a significant effect on the STH interannual anomaly. Our numerical experiment shows that the offshore SSTA-caused sensible heating may excite an anomalous anticyclonic circulation on the west side, which affects the intensity (area) and meridional position of the western Pacific STH.展开更多
The physical processes involved in the formation of the ENSO cycle,as well as the possible roles of the Hadley circulation （HC）,Walker circulation （WC）,and the propagating waves of the Southern Oscillation/Norther...The physical processes involved in the formation of the ENSO cycle,as well as the possible roles of the Hadley circulation （HC）,Walker circulation （WC）,and the propagating waves of the Southern Oscillation/Northern Oscillation （SO/NO） in its formation,were studied using composite and regression methods.The analysis showed that the convection and heat release triggered by ENSO in the central-eastern equatorial Pacific are the primary drivers for the 3-5 year cycle of the HC,WC and the meridional/zonal circulation.The HC plays a key role in the influence of ENSO on the circulation outside the tropics through angular momentum transportation.Meanwhile,the feedback effects of the anomalous circulation in the mid-high latitudes on ENSO are accomplished by the propagating waves of SO/NO associated with the evolutions of HC and WC.These propagating waves are the main agents of the connections among the meridional/zonal circulation outside the tropics,the Asian/Australian monsoon,the anomalous easterly/westerly winds over the tropical Pacific,and ENSO events.It was found that the 3-5 year cycle of the meridional/zonal circulation forced by ENSO is quite different from the several-week variation of the circulation index triggered by the inner dynamic processes of the atmosphere.The former occurs at the global scale with a definite flow pattern,while the latter occurs only in a wide area without a definite flow pattern.Finally,a physical model for the formation of the ENSO cycle composed of two fundamental processes at the basin and global scale,respectively,is proposed.展开更多
The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocea...The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocean（SPO） in boreal autumn are closely related to the variability in the dipole pattern of boreal winter precipitation over East Asia. The physical link between the boreal autumn SPO SSTAs and the boreal winter East Asian precipitation dipole pattern is shown to mainly be the seasonal persistence of the SPO SSTAs themselves. The seasonal persistence of the SPO SSTAs can memorize and transport the signal of the boreal autumn SSTAs to the following winter, and then stimulates a meridional teleconnection pattern from the SH to the NH, resulting in a meridional dipole pattern of atmospheric circulation over East Asia in boreal winter. As a major influencing factor, this dipole pattern of the atmospheric circulation can finally lead to the anomalous precipitation dipole pattern over East Asia in boreal winter. These observed physical processes are further confirmed in this study through numerical simulation. The evidence from this study, showing the impact of the SPO SSTAs in boreal autumn,not only deepens our understanding of the variability in East Asian boreal winter precipitation, but also provides a potentially useful predictor for precipitation in the region.展开更多
It is proved in this paper that NWP systematic forecast errors in the zonal mean circulation are due to the difference in westerly acceleration process during the forecasting period between model and real atmospheres....It is proved in this paper that NWP systematic forecast errors in the zonal mean circulation are due to the difference in westerly acceleration process during the forecasting period between model and real atmospheres. Those forcing factors which evoke the zonal mean wind variation can be split into various linear terms according to the non-acceleration theorem in a primitive equation system,By applying this tech- nique to the diagnosis of the forecast produets of the T42L9 model in January 1992 and in July 1992, it is indicated that the model has the ability to forecast the zonal mean wind to a reasonable extent, but there are still some errors in several places,especially in the upper troposphere and lower strato- sphere in the mid-latitude region as well as near the surface.The results of analysis by employing this scheme reveal the reason responsible for the systematic forecast errors of the zonal mean wind in the model and the possible way of improving it. It is also shown that non-acceleration theorem can be used as an efficient tool to diagnose the physical processes of NWP models.展开更多
This paper reviews the three-pattern decomposition of global atmospheric circulation(3P-DGAC)developed in recent years,including the decomposition model and the dynamical equations of global horizontal,meridional,and ...This paper reviews the three-pattern decomposition of global atmospheric circulation(3P-DGAC)developed in recent years,including the decomposition model and the dynamical equations of global horizontal,meridional,and zonal circulations.Compared with the traditional two-dimensional(2D)circulation decomposition method,the 3P-DGAC can effectively decompose the actual vertical vorticity into two components that are caused by the horizontal circulation and convergent/divergent movement(associated with the meridional and zonal circulations).It also decomposes the vertical velocity into the components of the meridional vertical circulation and the zonal vertical circulation,thus providing a new method to study the dynamical influences of convergent/divergent motions on the evolution of actual vertical vorticity and an accurate description of local vertical circulations.The 3P-DGAC is a three-dimensional(3D)circulation decomposition method based on the main characteristics of the actual atmospheric movements.The horizontal,meridional,and zonal circulations after the 3P-DGAC are the global generalization of Rossby waves in the middle-high latitudes and Hadley and Walker circulations in low latitudes.Therefore,the three-pattern decomposition model and its dynamical equations provide novel theoretical tools for studying complex interactions between middle-high and low latitude circulations as well as the physical mechanisms of the abnormal evolution of large-scale atmospheric circulations under the background of global warming.展开更多
基金supported by the Chinese Academy of Sciences key program under Grant KZCX3-SW-221the National Natural Science Foundation of China under Grant Nos.40620130113 and 40475037.
文摘The long-term relationship between the tree-ring-reconstructed annual precipitation in northeastern Mongolia （PRM） and the Northern Hemisphere Zonal Circulation （NHZC）, defined as the normalized zonal mean sea-level pressure at 60°N in May-June-July, is examined in this study. A significant correlation coefficient （0.31） was found between the NHZC indices and PRM based on the dataset for the period of 1872-1995. The mechanisms responsible for the relationship are discussed through analyses of the atmospheric general circulation variability associated with NHZC. It follows that NHZC-related atmospheric circulation variability provides an anomalous southeast flow from the ocean to Northeast Mongolia （northwest flow from Northeast Mongolia to the ocean） in the middle and low troposphere in positive （negative） phase of NHZC, resulting in more （less） water vapor transport to the target region and more （less） precipitation in Northeast Mongolia.
基金supported by the Chinese Youth 1000 Talents Program and the Open Project of the State Key Laboratory of Planetary Sciences, Macao University of Science and Technologysupported by the Science and Technology Facilities Council grant ST/R000891/1by the Macao Science and Technology Development Fund grants (007/2016/A1 and 001/2016/AFJ)
文摘To infer the internal equilibrium structure of a gaseous planet, especially the equation of state(EOS) and size of its inner core,requires accurate determination of lower-order zonal gravitational coefficients. Modeling of the gravitational signature associated with deep zonal circulation depends critically upon reliable subtraction of the dynamical components from totally derived gravitational coefficients. In the era of the Juno mission and the Grand Finale phase of the Cassini mission, it is timely and necessary to revisit and examine the so-called ‘Thermal Wind Equation(TWE)’, which has been extensively utilized to diagnose the dynamical parts of the gravitational fields measured by the two spacecrafts. TWE treats as negligible a few terms in the full equation of balance. However, the self-gravitational anomaly of the distorted fluid, unlike oblateness effects of solid-body rotation, is not a priori minor and thus should not be neglected in the name of approximation. Another equation, the ‘Thermal Gravitational Wind Equation(TGWE)’, includes this important additional term;we compare it with the TWE and show that physically the TGWE models a fundamentally different balance from the TWE and delivers numerical results considerably different from models based on the TWE. We conclude that the TWE balance cannot be relied upon to produce realistic convection models. Only after the TGWE balance is obtained can the relative importance of terms be assessed.The calculations we report here are based on two types of zonal circulations that are produced by realistically possible convections inside planets, instead of being constructed or assumed.
文摘The present work is intended to simulate, in a rotating annulus of stratified liquid, the me-chanical effect of the Xizang (Tibetan) Plateau on the zonal circulation. The main featuresof three flow patterns around the plateau for different Rossby number R and rotating Eulernumber E are analysed. and a division diagram of the flow pattern in (R, E) plane is given.It has been found that under the condition that similarity criterions R and E of the experimentalfluid are the same as those existing in the atmosphere for monthly mean states in spring, au-tumn and winter months, the experimental results are satisfied for the following weathersystems over the plateau and its vicinities: the low vortex, trough and shear line over thesoutheast part of the plateau, the tilted ridge over the northwest part of the plateau, the troughpatterns over the upstream and dewnstream of the plateau, the vertical circulation structure, thejets on both north and southeast sides of the plateau, and so on. This shows that the mechanicaleffect of the Tibetan Plateau on the general circulation over East Asia deserves close atten-tion.
基金The CAS/SAFEA International Partnership Program for Creative Research Teams of Chinese Academy of Sciencesthe National Natural Science Foundation of China under contract Nos 41422601,41376024 and 41376025
文摘Zonal overturning circulation （ZOC） and its associated zonal heat flux （ZHF） are important components of the oceanic circulation and climate system, although these conceptions have not received adequate attentions. Heaving induced by inter-annual and decadal wind stress perturbations can give rise to anomalous ZOC and ZHF. Based on a simple reduced gravity model, the anomalous ZOC and ZHF induced by idealized heaving modes in the world oceans are studied. For example, in a Pacific-like model basin intensified equatorial easterly on decadal time scales can lead to a negative ZOC with a non-negligible magnitude （-0.3×10^6 m^3/s） and a considerable westward ZHF with an amplitude of -11.2 TW. Thus, anomalous ZOC and ZHF may consist of a major part of climate signals on decadal time scales and thus play an important role in the oceanic circulation and climate change.
基金supported by the National Natural Science Foundation of China(Grant No.41975008)Key Laboratory of South China Sea Meteorological Disaster Prevention and Mitigation of Hainan Province(Grant No.SCSF201906)。
文摘This study reveals a significant positive connection between autumn non-tropical-cyclone heavy rainfall on Hainan Island and the intensity of Eastern Pacific(EP)El Ni?o events.That is,the amount of rainfall in super EP El Ni?o years is more than that in normal EP El Ni?o years.Comparing EP El Ni?o years of different intensities,the cooler sea surface temperature in the northwestern Pacific during super EP El Ni?o years stimulates a negative surface latent heat flux(LHF)anomaly and abnormal anticyclonic circulation at 850 hPa.Under these conditions,an abnormal zonal vertical circulation develops in the northern South China Sea once a positive LHF anomaly and abnormal cyclonic circulation(ACC)at 850hPa occur in the Beibu Gulf.The abnormal zonal vertical circulation further strengthens the ascending motion over Hainan Island,as the critical factor that leads to excessive rainfall.Further analysis shows that the positive LHF anomaly,which can be attributed to the increased latent heat transfer which resulted from the increased surface wind speed,is an important trigger for the ACC.However,the ACC is also the supplier of favorable moisture conditions because it intensifies vapor convergence over Hainan Island and meridionally transports moisture from the South China Sea to northeastern Hainan Island,thereby generating heavy rainfall.This paper emphasizes that the impact of El Ni?o events,especially super El Ni?o events,on rainfall over Hainan Island cannot be ignored,even if the traditional view is that frequent rainfall occurs mainly in La Ni?a years.
基金The National Natural Science Foundation of China (No.49635170)The program of Study on Regional Climate Variation and Mechani
文摘The paper investigates the vertical circulation structure of the western Pacific subtropical high (STH) and its interannual variation features in relation tO East Asian subtropical summer monsoon and external thermal forcing by using the high-resolution and good-quality observations from the 1998 South China Sea Summer Monsoon Experiment (SCSMEX), the NCEP 40-year reanalysis data and relevant SST and the STH parameters. It is found that the vertical circulation structures differ greatly in features between quasi-Stationary and transient components of the western Pacific STH. When rainstorms happen in the rainband of East Asian subtropical monsoon on the STH north side, the downdrafts are distinct around the ridge at a related meridian. The sinking at high (low) levels comes from the north (south) side of the STH, thereby revealing that the high is a tie between tropical and extratropical systems. The analyses of this paper suggest that the latent heat release associated with subtropical monsoon precipitation, the offshore SST and East Asian land-sea thermal contrast have a significant effect on the STH interannual anomaly. Our numerical experiment shows that the offshore SSTA-caused sensible heating may excite an anomalous anticyclonic circulation on the west side, which affects the intensity (area) and meridional position of the western Pacific STH.
基金supported by the National Natural Science Foundation of China (Grant No.41375055)the National Basic Research Program of China (Grant No.2012CB957804)+1 种基金the Key Technologies R&D Program (Grant No.2009BAC51B02)the State Grid Science & Technology Project (GC71-13-007)
文摘The physical processes involved in the formation of the ENSO cycle,as well as the possible roles of the Hadley circulation （HC）,Walker circulation （WC）,and the propagating waves of the Southern Oscillation/Northern Oscillation （SO/NO） in its formation,were studied using composite and regression methods.The analysis showed that the convection and heat release triggered by ENSO in the central-eastern equatorial Pacific are the primary drivers for the 3-5 year cycle of the HC,WC and the meridional/zonal circulation.The HC plays a key role in the influence of ENSO on the circulation outside the tropics through angular momentum transportation.Meanwhile,the feedback effects of the anomalous circulation in the mid-high latitudes on ENSO are accomplished by the propagating waves of SO/NO associated with the evolutions of HC and WC.These propagating waves are the main agents of the connections among the meridional/zonal circulation outside the tropics,the Asian/Australian monsoon,the anomalous easterly/westerly winds over the tropical Pacific,and ENSO events.It was found that the 3-5 year cycle of the meridional/zonal circulation forced by ENSO is quite different from the several-week variation of the circulation index triggered by the inner dynamic processes of the atmosphere.The former occurs at the global scale with a definite flow pattern,while the latter occurs only in a wide area without a definite flow pattern.Finally,a physical model for the formation of the ENSO cycle composed of two fundamental processes at the basin and global scale,respectively,is proposed.
基金jointly supported by the Special Fund for Public Welfare Industry (meteorology) (Grant No. GYHY201306026)the National Natural Science Foundation of China (Grant Nos. 41421004 and 41522503)
文摘The possible mechanism behind the variability in the dipole pattern of boreal winter precipitation over East Asia is analyzed in this study. The results show that the SST anomalies（SSTAs） over the South Pacific Ocean（SPO） in boreal autumn are closely related to the variability in the dipole pattern of boreal winter precipitation over East Asia. The physical link between the boreal autumn SPO SSTAs and the boreal winter East Asian precipitation dipole pattern is shown to mainly be the seasonal persistence of the SPO SSTAs themselves. The seasonal persistence of the SPO SSTAs can memorize and transport the signal of the boreal autumn SSTAs to the following winter, and then stimulates a meridional teleconnection pattern from the SH to the NH, resulting in a meridional dipole pattern of atmospheric circulation over East Asia in boreal winter. As a major influencing factor, this dipole pattern of the atmospheric circulation can finally lead to the anomalous precipitation dipole pattern over East Asia in boreal winter. These observed physical processes are further confirmed in this study through numerical simulation. The evidence from this study, showing the impact of the SPO SSTAs in boreal autumn,not only deepens our understanding of the variability in East Asian boreal winter precipitation, but also provides a potentially useful predictor for precipitation in the region.
文摘It is proved in this paper that NWP systematic forecast errors in the zonal mean circulation are due to the difference in westerly acceleration process during the forecasting period between model and real atmospheres. Those forcing factors which evoke the zonal mean wind variation can be split into various linear terms according to the non-acceleration theorem in a primitive equation system,By applying this tech- nique to the diagnosis of the forecast produets of the T42L9 model in January 1992 and in July 1992, it is indicated that the model has the ability to forecast the zonal mean wind to a reasonable extent, but there are still some errors in several places,especially in the upper troposphere and lower strato- sphere in the mid-latitude region as well as near the surface.The results of analysis by employing this scheme reveal the reason responsible for the systematic forecast errors of the zonal mean wind in the model and the possible way of improving it. It is also shown that non-acceleration theorem can be used as an efficient tool to diagnose the physical processes of NWP models.
基金supported by the National Key R&D Program of China(Grant No.2017YFC1502305)the National Natural Science Foundation of China(Grant Nos.41775069&41975076)。
文摘This paper reviews the three-pattern decomposition of global atmospheric circulation(3P-DGAC)developed in recent years,including the decomposition model and the dynamical equations of global horizontal,meridional,and zonal circulations.Compared with the traditional two-dimensional(2D)circulation decomposition method,the 3P-DGAC can effectively decompose the actual vertical vorticity into two components that are caused by the horizontal circulation and convergent/divergent movement(associated with the meridional and zonal circulations).It also decomposes the vertical velocity into the components of the meridional vertical circulation and the zonal vertical circulation,thus providing a new method to study the dynamical influences of convergent/divergent motions on the evolution of actual vertical vorticity and an accurate description of local vertical circulations.The 3P-DGAC is a three-dimensional(3D)circulation decomposition method based on the main characteristics of the actual atmospheric movements.The horizontal,meridional,and zonal circulations after the 3P-DGAC are the global generalization of Rossby waves in the middle-high latitudes and Hadley and Walker circulations in low latitudes.Therefore,the three-pattern decomposition model and its dynamical equations provide novel theoretical tools for studying complex interactions between middle-high and low latitude circulations as well as the physical mechanisms of the abnormal evolution of large-scale atmospheric circulations under the background of global warming.
