The Aleutian Low(AL)is a dominant feature of the mean circulation in the North Pacific during the winter season.The background stationary wave,air-sea interaction,and transient eddies over the North Pacific exert dist...The Aleutian Low(AL)is a dominant feature of the mean circulation in the North Pacific during the winter season.The background stationary wave,air-sea interaction,and transient eddies over the North Pacific exert distinct impacts on the interannual variations of the AL intensity and position.In this study,we adopt the quasi-geostrophic geopotential tendency equation to investigate the roles of various physical processes in the maintenance and interannual variations of this system.The results show that absolute vorticity advection plays the most important role in the formation and maintenance of AL intensity,while high-frequency transient eddies contribute most to the meridional and zonal shifts of the AL.The high-frequency transient eddy vorticity forcing affects the AL through the barotropic energy conversion process,and,in turn,the AL enhances the high-frequency transient eddies through the baroclinic energy conversion process,forming a positive feedback.The associated high-frequency eddy kinetic energy anomalies exhibit an eastward movement toward the east coast of North America in the years of an intensified AL,which explains why a strengthened AL is often accompanied by an eastward movement.Furthermore,the energy conversion terms of high-frequency transient eddies are mostly located over the extratropical eastern North Pacific,leading to asymmetric features in the zonal movement of the AL.展开更多
Both the level of the high-frequency eddy kinetic energy（HF-EKE） and the energy-containing scale in the upstream Kuroshio Extension（KE） undergo a well-defined decadal modulation, which correlates well with the dec...Both the level of the high-frequency eddy kinetic energy（HF-EKE） and the energy-containing scale in the upstream Kuroshio Extension（KE） undergo a well-defined decadal modulation, which correlates well with the decadal KE path variability. The HF-EKE level and the energy-containing scales will increase with unstable KE path and decrease with stable KE path. Also the mesoscale eddies are a little meridionally elongated in the stable state, while they are much zonally elongated in the unstable state. The local baroclinic instability and the barotropic instability associated with the decadal modulation of HF-EKE have been investigated. The results show that the baroclinic instability is stronger in the stable state than that in the unstable state, with a shorter characteristic temporal scale and a larger characteristic spatial scale. Meanwhile, the regional-averaged barotropic conversion rate is larger in the unstable state than that in the stable state. The results also demonstrate that the baroclinic instability is not the dominant mechanism influencing the decadal modulation of the mesoscale eddy field, while the barotropic instability makes a positive contribution to the decadal modulation.展开更多
Based on 25-year（1987–2011） tropical cyclone（TC） best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pa...Based on 25-year（1987–2011） tropical cyclone（TC） best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pacific. Interaction was defined as the absolute value of eddy momentum flux convergence（EFC） exceeding 10 m s^（-1）d^（-1）. Based on this definition, it was found that 18% of all six-hourly TC samples experienced interaction. Extreme interaction cases showed that EFC can reach^120 m s^（-1）d^（-1） during the extratropical-cyclone（EC） stage, an order of magnitude larger than reported in previous studies.Composite analysis showed that positive interactions are characterized by a double-jet flow pattern, rather than the traditional trough pattern, because it is the jets that bring in large EFC from the upper-level environment to the TC center. The role of the outflow jet is also enhanced by relatively low inertial stability, as compared to the inflow jet. Among several environmental factors, it was found that extremely large EFC is usually accompanied by high inertial stability, low SST and strong vertical wind shear（VWS）. Thus, the positive effect of EFC is cancelled by their negative effects. Only those samples during the EC stage, whose intensities were less dependent on VWS and the underlying SST, could survive in extremely large EFC environments, or even re-intensify. For classical TCs（not in the EC stage）, it was found that environments with a moderate EFC value generally below ~25 m s^（-1）d^（-1） are more favorable for a TC＇s intensification than those with extremely large EFC.展开更多
A variable coefficient Korteweg de Vries （VCKdV） system is derived by considering the time-dependent basic flow and boundary conditions from the well-known Euler equation with an earth rotation term. The analytical ...A variable coefficient Korteweg de Vries （VCKdV） system is derived by considering the time-dependent basic flow and boundary conditions from the well-known Euler equation with an earth rotation term. The analytical solution obtained from the VCKdV equation can be successfully used to explain fruitful phenomena in fluid and other physical fields, for instance, the atmospheric blocking phenomena. In particular, a diploe blocking case happened during 9 April 1973 to 18 April 1973 read out from the National Center for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） reanalysis data is well described by the analytical solution.展开更多
In this paper, the creation and annihilation of turbulent eddies are described as elementary particles in the quantum field theory. An elementary particle mav be considered as a solid entity as it exists in quantum th...In this paper, the creation and annihilation of turbulent eddies are described as elementary particles in the quantum field theory. An elementary particle mav be considered as a solid entity as it exists in quantum theory, but a turbulent eddy is often changed in size and shape with time due to its energy dissipation in a turbulent field. Therefore, in order to apply the method of the quantum field theory to the turbulent field by analogy, the entity of the same eddy should be defined firstly According to the linearized theory, the turbulent eddies with the similarity character in time duration may be considered as the entity of the same eddy, and the creation and annihilation of turbulent eddies without the similar characters are related to the interaction term in equation (2.6). Then, the creation operator and annihilation operator similar-to those in the quantum field theory are used to describe the state of turbulent eddy field. Finally, a 'Schrddinger' equation of turbulent eddies is formulated based upon the nonlinear terms in the original N- S equation. Thus, a new turbulent eddy interaction theory similar to the quantum field theory is obtained.展开更多
The barotropic processes associated with the development of a precipitation system are investigated through analysis of cloud-resolving model simulations of Mei-yu torrential rainfall events over eastern China in mid-...The barotropic processes associated with the development of a precipitation system are investigated through analysis of cloud-resolving model simulations of Mei-yu torrential rainfall events over eastern China in mid-June 2011. During the model integration period, there were three major heavy rainfall events： 9–12, 13–16 and 16–20 June. The kinetic energy is converted from perturbation to mean circulations in the first and second period, whereas it is converted from mean to perturbation circulations in the third period. Further analysis shows that kinetic energy conversion is determined by vertical transport of zonal momentum. Thus, the prognostic equation of vertical transport of zonal momentum is derived, in which its tendency is associated with dynamic, pressure gradient and buoyancy processes. The kinetic energy conversion from perturbation to mean circulations in the first period is mainly associated with the dynamic processes. The kinetic energy conversion from mean to perturbation circulations in the third period is generally related to the pressure gradient processes.展开更多
In development of baroclinic disturbances, baroclinity of basic temperature field varies with conversion of available potential energy. The growth rate which depends on the baroclinity varies as well. However, in prev...In development of baroclinic disturbances, baroclinity of basic temperature field varies with conversion of available potential energy. The growth rate which depends on the baroclinity varies as well. However, in previous linear theories, the growth rate was considered constant, so development of disturbances was not constrained by energy sources in the linear theories. In terms of energy conservation and conversion in an isolated atmosphere, we may study the variations in the baroclinity and growth rate and draw the corresponding pictures of perturbation developments in the varying environments. The amplification for the most unstable Eady wave is discussed as an example. It will be found that growth of baroclinic perturbations constrained by energy conservation is significantly different from the growth at the initial constant rate after mature stage.展开更多
In this paper,Eliassen-Palm theory and associated diagnostic method are used to discuss the dynamical mechanism of the interaction between eddy flux and zonal averaged flow in the sudden change of the general circulat...In this paper,Eliassen-Palm theory and associated diagnostic method are used to discuss the dynamical mechanism of the interaction between eddy flux and zonal averaged flow in the sudden change of the general circulation in the Northern Hemisphere in early summer of 1982,which indicates that the northward jump of subtropic jet stream is closely related to the enhanced transport of mid-latitude eddy energy to the subtropic tro- popause.However,the direction of the transport is conditioned by the structure of zonal averaged flow.It is evident that the adjustment of zonal averaged flow responses quickly to the eddy transport during this episode. As regard to the suddenness of the change of circulation,the critical role is played by the eddy forcing,展开更多
基金partially supported by the National Natural Science Foundation of China(Grant Nos.42088101 and 42175023)the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant No.316323005)the Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies(Grant No.2020B1212060025)。
文摘The Aleutian Low(AL)is a dominant feature of the mean circulation in the North Pacific during the winter season.The background stationary wave,air-sea interaction,and transient eddies over the North Pacific exert distinct impacts on the interannual variations of the AL intensity and position.In this study,we adopt the quasi-geostrophic geopotential tendency equation to investigate the roles of various physical processes in the maintenance and interannual variations of this system.The results show that absolute vorticity advection plays the most important role in the formation and maintenance of AL intensity,while high-frequency transient eddies contribute most to the meridional and zonal shifts of the AL.The high-frequency transient eddy vorticity forcing affects the AL through the barotropic energy conversion process,and,in turn,the AL enhances the high-frequency transient eddies through the baroclinic energy conversion process,forming a positive feedback.The associated high-frequency eddy kinetic energy anomalies exhibit an eastward movement toward the east coast of North America in the years of an intensified AL,which explains why a strengthened AL is often accompanied by an eastward movement.Furthermore,the energy conversion terms of high-frequency transient eddies are mostly located over the extratropical eastern North Pacific,leading to asymmetric features in the zonal movement of the AL.
基金The National Natural Science Foundation of China under contract No.41276026the Special Fund for Strategic Pilot Technology Chinese Academy of Sciences under contract No.XDA11020301the Joint Fund between Natural Science Foundation of China and Shandong Province under contract No.U1406401
文摘Both the level of the high-frequency eddy kinetic energy（HF-EKE） and the energy-containing scale in the upstream Kuroshio Extension（KE） undergo a well-defined decadal modulation, which correlates well with the decadal KE path variability. The HF-EKE level and the energy-containing scales will increase with unstable KE path and decrease with stable KE path. Also the mesoscale eddies are a little meridionally elongated in the stable state, while they are much zonally elongated in the unstable state. The local baroclinic instability and the barotropic instability associated with the decadal modulation of HF-EKE have been investigated. The results show that the baroclinic instability is stronger in the stable state than that in the unstable state, with a shorter characteristic temporal scale and a larger characteristic spatial scale. Meanwhile, the regional-averaged barotropic conversion rate is larger in the unstable state than that in the stable state. The results also demonstrate that the baroclinic instability is not the dominant mechanism influencing the decadal modulation of the mesoscale eddy field, while the barotropic instability makes a positive contribution to the decadal modulation.
基金jointly sponsored by the National Natural Science Foundation of China(Grant Nos.41205032,41405048 and 41375050)China Special Fund for Meteorological Research in the Public Interest(Grant No.GYHY201406008)the Guangdong Marine Disaster Emergency Response Technology Research Center(2012A032100004)
文摘Based on 25-year（1987–2011） tropical cyclone（TC） best track data, a statistical study was carried out to investigate the basic features of upper-tropospheric TC–environment interactions over the western North Pacific. Interaction was defined as the absolute value of eddy momentum flux convergence（EFC） exceeding 10 m s^（-1）d^（-1）. Based on this definition, it was found that 18% of all six-hourly TC samples experienced interaction. Extreme interaction cases showed that EFC can reach^120 m s^（-1）d^（-1） during the extratropical-cyclone（EC） stage, an order of magnitude larger than reported in previous studies.Composite analysis showed that positive interactions are characterized by a double-jet flow pattern, rather than the traditional trough pattern, because it is the jets that bring in large EFC from the upper-level environment to the TC center. The role of the outflow jet is also enhanced by relatively low inertial stability, as compared to the inflow jet. Among several environmental factors, it was found that extremely large EFC is usually accompanied by high inertial stability, low SST and strong vertical wind shear（VWS）. Thus, the positive effect of EFC is cancelled by their negative effects. Only those samples during the EC stage, whose intensities were less dependent on VWS and the underlying SST, could survive in extremely large EFC environments, or even re-intensify. For classical TCs（not in the EC stage）, it was found that environments with a moderate EFC value generally below ~25 m s^（-1）d^（-1） are more favorable for a TC＇s intensification than those with extremely large EFC.
基金Supported by the National Natural Science Foundation of China under Grant Nos 90203001, 10475055, 10547124 and 40305009.
文摘A variable coefficient Korteweg de Vries （VCKdV） system is derived by considering the time-dependent basic flow and boundary conditions from the well-known Euler equation with an earth rotation term. The analytical solution obtained from the VCKdV equation can be successfully used to explain fruitful phenomena in fluid and other physical fields, for instance, the atmospheric blocking phenomena. In particular, a diploe blocking case happened during 9 April 1973 to 18 April 1973 read out from the National Center for Environmental Prediction/National Center for Atmospheric Research （NCEP/NCAR） reanalysis data is well described by the analytical solution.
文摘In this paper, the creation and annihilation of turbulent eddies are described as elementary particles in the quantum field theory. An elementary particle mav be considered as a solid entity as it exists in quantum theory, but a turbulent eddy is often changed in size and shape with time due to its energy dissipation in a turbulent field. Therefore, in order to apply the method of the quantum field theory to the turbulent field by analogy, the entity of the same eddy should be defined firstly According to the linearized theory, the turbulent eddies with the similarity character in time duration may be considered as the entity of the same eddy, and the creation and annihilation of turbulent eddies without the similar characters are related to the interaction term in equation (2.6). Then, the creation operator and annihilation operator similar-to those in the quantum field theory are used to describe the state of turbulent eddy field. Finally, a 'Schrddinger' equation of turbulent eddies is formulated based upon the nonlinear terms in the original N- S equation. Thus, a new turbulent eddy interaction theory similar to the quantum field theory is obtained.
基金supported by the National Natural Science Foundation of China (Grant No. 41475039)National Key Basic Research and Development Project of China (Grant No. 2015CB953601).
文摘The barotropic processes associated with the development of a precipitation system are investigated through analysis of cloud-resolving model simulations of Mei-yu torrential rainfall events over eastern China in mid-June 2011. During the model integration period, there were three major heavy rainfall events： 9–12, 13–16 and 16–20 June. The kinetic energy is converted from perturbation to mean circulations in the first and second period, whereas it is converted from mean to perturbation circulations in the third period. Further analysis shows that kinetic energy conversion is determined by vertical transport of zonal momentum. Thus, the prognostic equation of vertical transport of zonal momentum is derived, in which its tendency is associated with dynamic, pressure gradient and buoyancy processes. The kinetic energy conversion from perturbation to mean circulations in the first period is mainly associated with the dynamic processes. The kinetic energy conversion from mean to perturbation circulations in the third period is generally related to the pressure gradient processes.
文摘In development of baroclinic disturbances, baroclinity of basic temperature field varies with conversion of available potential energy. The growth rate which depends on the baroclinity varies as well. However, in previous linear theories, the growth rate was considered constant, so development of disturbances was not constrained by energy sources in the linear theories. In terms of energy conservation and conversion in an isolated atmosphere, we may study the variations in the baroclinity and growth rate and draw the corresponding pictures of perturbation developments in the varying environments. The amplification for the most unstable Eady wave is discussed as an example. It will be found that growth of baroclinic perturbations constrained by energy conservation is significantly different from the growth at the initial constant rate after mature stage.
文摘In this paper,Eliassen-Palm theory and associated diagnostic method are used to discuss the dynamical mechanism of the interaction between eddy flux and zonal averaged flow in the sudden change of the general circulation in the Northern Hemisphere in early summer of 1982,which indicates that the northward jump of subtropic jet stream is closely related to the enhanced transport of mid-latitude eddy energy to the subtropic tro- popause.However,the direction of the transport is conditioned by the structure of zonal averaged flow.It is evident that the adjustment of zonal averaged flow responses quickly to the eddy transport during this episode. As regard to the suddenness of the change of circulation,the critical role is played by the eddy forcing,
