A method of linear momentum approximation is proposed that deals with weak nonlinear problems in an approximate manner. A motion of nonlinear nature is obtained in the system by assuming the motion to be in the form o...A method of linear momentum approximation is proposed that deals with weak nonlinear problems in an approximate manner. A motion of nonlinear nature is obtained in the system by assuming the motion to be in the form of linear momentum flow in the corresponding space introduced, followed by the transformation from the specified into a physical space. Significant results have been thereby derived in examining the effects of baroclinic Ekman momentum flow upon Eady-type baroclinic waves and frontogenesis. Also, this technique can be applied to investigate the dynamic characteristics of the weak nonlinear boundary layer including topography, stratification and non-Ekmantype friction for gaining further insight into the influence on the boundary layer inner parameters of terrain, baroclinicity and inhomogeneous process so that the classic theory is revised.展开更多
Closed-form and asymptotic solutions are derived for the steady, fully-developed hydromagnetic free and forced convection flow in a rotating horizontal parallel-plate channel under the action of an inclined magnetic f...Closed-form and asymptotic solutions are derived for the steady, fully-developed hydromagnetic free and forced convection flow in a rotating horizontal parallel-plate channel under the action of an inclined magnetic field and constant pressure gradient along the longitudinal axis of the channel. The magnetic field is strong enough to generate Hall current effects and the magnetic Reynolds number of sufficient magnitude that induced magnetic field effects are also present. Secondary flow is present owing to the Hall current effect. The channel plates are also taken to be electrically-conducting. The conservation equations are formulated in an (x, y, z) coordinate system and non-dimensionalized using appropriate transformations. The resulting non-dimensional coupled ordinary differential equations for primary and secondary velocity components and primary and secondary induced magnetic field components and transformed boundary conditions are shown to be controlled by the dimensionless pressure gradient parameter (px), Hartmann number (M2), Grashof number (G), Hall current parameter (m), rotational parameter (K2), magnetic field inclination (Θ), and the electrical conductance ratios of the upper (⏱) and lower (⏲) plates. Solutions are derived using the method of complex variables. Asymptotic solutions are also presented for very high rotation parameter and Hartmann number of order equal to unity, for which Ekman-Hartmann boundary layers are identified at the plates. A parametric study of the evolution of velocity and induced magnetic field distributions is undertaken. It is shown that generally increasing Hall current effect (m) serves to accentuate the secondary (cross) flow but oppose the primary flow. An increase in rotational parameter (K2) is also found to counteract primary flow intensity. An elevation in the Grashof number i.e. free convection parameter (G) is shown to aid the secondary induced magnetic field component (Hz);however there is a decrease in magnitudes of the primary induced magnetic field component (Hx) with increasing Grashof number. Increasing inclination of the applied magnetic field (Θ, is also found to oppose the primary flow (u1) but conversely to strongly assist the secondary flow (w1). Both critical primary (Gcx) and secondary (Gcz)Grashof numbers are shown to be reduced with increasing inclination of the magnetic field (Θ), increasing Hall parameter (m) and rotational parameter (K2). Applications of the study arise in rotating MHD induction power generators and also astrophysical flows.展开更多
With the Ekman momentum approximation, the four important pseudo-conservation relations in the boundary layer dynamics are derived. In order to simplify the problem, the so-called Ekman coordinates is introduced. The ...With the Ekman momentum approximation, the four important pseudo-conservation relations in the boundary layer dynamics are derived. In order to simplify the problem, the so-called Ekman coordinates is introduced. The motion in Ekman coordinates is classical Ekman flow. However, the solution in Ekman coordinates should be converted into the physical coordinates. In this paper, an approximation transformation is used to discuss the inuflence of the turbulence friction on the baroclinic wave of Eady type and frontogenesis. The results show that, on one hand, Ekman momentum flow implicates the ageostrophic component which enhances frontogenesis in the boundary layer, on the other hand, it implies the turbulence friction which weakens the frontogenesis in the boundary layer. The critical time of the discontinuity occurring in the boundary layer is longer than that in the free atmosphere. Ekman momentum flow is dualistic.展开更多
It is convenient to use σ-coordinates to discuss the dynamic effect of orography and the flow in Ekman boundary layer.In this paper,the theory of mixing length is generalized to the σ-coordinate system. Then the gov...It is convenient to use σ-coordinates to discuss the dynamic effect of orography and the flow in Ekman boundary layer.In this paper,the theory of mixing length is generalized to the σ-coordinate system. Then the governing equations,describing the motion in the boundary layer over the mountain regions are derived.The features of flow in the boundary layer,especially the effects of Ekman pumping,are discussed in details.It is pointed out that there are three factors affecting the vertical motion at the top of the boun- dary layer:(1)vorticity distribution in the boundary layer,which is directly related to the divergence and convergence of air flow caused by friction,(2)the upslope or downslope motion of flow over the mountain slopes,and(3)the mutual effect of orography and friction induced by the ageostrophic component climbing up- ward or downward in the boundary layer over mountain regions.展开更多
With the Ekman momentum approximation,the influence of atmospheric baroclinity on the dynamics of boundary layer is studied.Some new results are obtained.These results show that the atmospheric baroclinity plays an im...With the Ekman momentum approximation,the influence of atmospheric baroclinity on the dynamics of boundary layer is studied.Some new results are obtained.These results show that the atmospheric baroclinity plays an important role in altering the horizontal velocity of Ekman boundary layer and its angle with the horizontal wind velocity compo- nent near the surface.There are three different physical factors affecting the nonlinear Ekman suction,the vertical mo- tion at the top of boundary layer:first,barotropic geostrophic relative vorticity at the ground;second,the thermal wind vorticity induced by the baroclinity;and third,the nonlinear interaction between the barotropic geostrophic relative vorticity and the baroclinic thermal wind vorticity.These results may provide a better physical basis for the parameterization of boundary layer and the interpretation of the numerical modeling results.展开更多
In this paper, the eddy coefficient and the treatment for dividing layers of Estoque's numerical model in modern PBL dynamics have been applied to derive order-zero and order-one analytic solutions over large-scal...In this paper, the eddy coefficient and the treatment for dividing layers of Estoque's numerical model in modern PBL dynamics have been applied to derive order-zero and order-one analytic solutions over large-scale topography, the solutions are used to obtain the divergence and vertical velocity, improving the previous results.展开更多
The effects of typhoon intrusion on the Guangdong coastal upwelling system were investigated on the basis of in situ CTD (conductivity-temperature-depth) cruise observations and especially upward-looking ADCP (Acousti...The effects of typhoon intrusion on the Guangdong coastal upwelling system were investigated on the basis of in situ CTD (conductivity-temperature-depth) cruise observations and especially upward-looking ADCP (Acoustic Doppler Current Profil- ers) measurements obtained from a comprehensive survey of the Guangdong coastal region carried out by the Chinese Off-shore Investigation and Assessment Project in the summer of 2006. It was found that northeastward geostrophic advection driven by the summer monsoon has a significant near-seabed onshore component adjacent to Shantou, which in conjunction with upper-level offshore Ekman flow, constitutes the canonical Guangdong coastal upwelling system. Further analyses suggested that the Guangdong coastal upwelling system is sensitive to subtle changes in the typhoon intensity and migration pathway. On one hand, as a typhoon approaches from north of the upwelling system (e.g. Typhoon 0604 (Bilis) and Typhoon 0605 (Kaemi)) in the early phase of intrusion, the enhanced southwesterly leads to exceptional enhancement of the onshore flow; i.e., enhanced upwelling. Afterward, irrespective of the forced ocean responses resulting from the stronger local winds (Typhoon 0604) or the moderate typhoon-induced inertial oscillations (Typhoon 0605), the situation is not conducive to sustaining a stable, persistent upwelling system. On the other hand, when there is typhoon intrusion south of the upwelling system (e.g. Typhoon 0606 (Prapiroon)), the favorable southwesterly tends to be substituted by an anomalous northeasterly, which destroys the traditional coastal upwelling pattern. However, the canonical upwelling system tends to recover within 1-2 days of the typhoon passing.展开更多
文摘A method of linear momentum approximation is proposed that deals with weak nonlinear problems in an approximate manner. A motion of nonlinear nature is obtained in the system by assuming the motion to be in the form of linear momentum flow in the corresponding space introduced, followed by the transformation from the specified into a physical space. Significant results have been thereby derived in examining the effects of baroclinic Ekman momentum flow upon Eady-type baroclinic waves and frontogenesis. Also, this technique can be applied to investigate the dynamic characteristics of the weak nonlinear boundary layer including topography, stratification and non-Ekmantype friction for gaining further insight into the influence on the boundary layer inner parameters of terrain, baroclinicity and inhomogeneous process so that the classic theory is revised.
文摘Closed-form and asymptotic solutions are derived for the steady, fully-developed hydromagnetic free and forced convection flow in a rotating horizontal parallel-plate channel under the action of an inclined magnetic field and constant pressure gradient along the longitudinal axis of the channel. The magnetic field is strong enough to generate Hall current effects and the magnetic Reynolds number of sufficient magnitude that induced magnetic field effects are also present. Secondary flow is present owing to the Hall current effect. The channel plates are also taken to be electrically-conducting. The conservation equations are formulated in an (x, y, z) coordinate system and non-dimensionalized using appropriate transformations. The resulting non-dimensional coupled ordinary differential equations for primary and secondary velocity components and primary and secondary induced magnetic field components and transformed boundary conditions are shown to be controlled by the dimensionless pressure gradient parameter (px), Hartmann number (M2), Grashof number (G), Hall current parameter (m), rotational parameter (K2), magnetic field inclination (Θ), and the electrical conductance ratios of the upper (⏱) and lower (⏲) plates. Solutions are derived using the method of complex variables. Asymptotic solutions are also presented for very high rotation parameter and Hartmann number of order equal to unity, for which Ekman-Hartmann boundary layers are identified at the plates. A parametric study of the evolution of velocity and induced magnetic field distributions is undertaken. It is shown that generally increasing Hall current effect (m) serves to accentuate the secondary (cross) flow but oppose the primary flow. An increase in rotational parameter (K2) is also found to counteract primary flow intensity. An elevation in the Grashof number i.e. free convection parameter (G) is shown to aid the secondary induced magnetic field component (Hz);however there is a decrease in magnitudes of the primary induced magnetic field component (Hx) with increasing Grashof number. Increasing inclination of the applied magnetic field (Θ, is also found to oppose the primary flow (u1) but conversely to strongly assist the secondary flow (w1). Both critical primary (Gcx) and secondary (Gcz)Grashof numbers are shown to be reduced with increasing inclination of the magnetic field (Θ), increasing Hall parameter (m) and rotational parameter (K2). Applications of the study arise in rotating MHD induction power generators and also astrophysical flows.
基金This work is supported by the National Natural Science Foundation of China
文摘With the Ekman momentum approximation, the four important pseudo-conservation relations in the boundary layer dynamics are derived. In order to simplify the problem, the so-called Ekman coordinates is introduced. The motion in Ekman coordinates is classical Ekman flow. However, the solution in Ekman coordinates should be converted into the physical coordinates. In this paper, an approximation transformation is used to discuss the inuflence of the turbulence friction on the baroclinic wave of Eady type and frontogenesis. The results show that, on one hand, Ekman momentum flow implicates the ageostrophic component which enhances frontogenesis in the boundary layer, on the other hand, it implies the turbulence friction which weakens the frontogenesis in the boundary layer. The critical time of the discontinuity occurring in the boundary layer is longer than that in the free atmosphere. Ekman momentum flow is dualistic.
基金This work was supported by the National Natural Science Foundation of China under Contract 4860222.
文摘It is convenient to use σ-coordinates to discuss the dynamic effect of orography and the flow in Ekman boundary layer.In this paper,the theory of mixing length is generalized to the σ-coordinate system. Then the governing equations,describing the motion in the boundary layer over the mountain regions are derived.The features of flow in the boundary layer,especially the effects of Ekman pumping,are discussed in details.It is pointed out that there are three factors affecting the vertical motion at the top of the boun- dary layer:(1)vorticity distribution in the boundary layer,which is directly related to the divergence and convergence of air flow caused by friction,(2)the upslope or downslope motion of flow over the mountain slopes,and(3)the mutual effect of orography and friction induced by the ageostrophic component climbing up- ward or downward in the boundary layer over mountain regions.
文摘With the Ekman momentum approximation,the influence of atmospheric baroclinity on the dynamics of boundary layer is studied.Some new results are obtained.These results show that the atmospheric baroclinity plays an important role in altering the horizontal velocity of Ekman boundary layer and its angle with the horizontal wind velocity compo- nent near the surface.There are three different physical factors affecting the nonlinear Ekman suction,the vertical mo- tion at the top of boundary layer:first,barotropic geostrophic relative vorticity at the ground;second,the thermal wind vorticity induced by the baroclinity;and third,the nonlinear interaction between the barotropic geostrophic relative vorticity and the baroclinic thermal wind vorticity.These results may provide a better physical basis for the parameterization of boundary layer and the interpretation of the numerical modeling results.
基金This work was supported by National Natural Science Foundation of China
文摘In this paper, the eddy coefficient and the treatment for dividing layers of Estoque's numerical model in modern PBL dynamics have been applied to derive order-zero and order-one analytic solutions over large-scale topography, the solutions are used to obtain the divergence and vertical velocity, improving the previous results.
基金supported by the Chinese Offshore Physical Oceanography and Marine Meteorology Investigation and Assessment Project (Grant No.908-ZC-I-01)the Chinese Main Estuarine Dynamic Sedimentary Processand Its Impacts on Coastal Economic Development (Grant No.908-02-01-04)+2 种基金the Chinese Main Estuarine and the Adjacent Sea Environmental Quality Evaluation (Grant No. 908-02-02-02)the National Natural Science Foundation of China (Grant Nos. 40806013 and 41176031)the China Ocean University Physical Oceanography Key Laboratory Open Fund (Grant No. 200904)
文摘The effects of typhoon intrusion on the Guangdong coastal upwelling system were investigated on the basis of in situ CTD (conductivity-temperature-depth) cruise observations and especially upward-looking ADCP (Acoustic Doppler Current Profil- ers) measurements obtained from a comprehensive survey of the Guangdong coastal region carried out by the Chinese Off-shore Investigation and Assessment Project in the summer of 2006. It was found that northeastward geostrophic advection driven by the summer monsoon has a significant near-seabed onshore component adjacent to Shantou, which in conjunction with upper-level offshore Ekman flow, constitutes the canonical Guangdong coastal upwelling system. Further analyses suggested that the Guangdong coastal upwelling system is sensitive to subtle changes in the typhoon intensity and migration pathway. On one hand, as a typhoon approaches from north of the upwelling system (e.g. Typhoon 0604 (Bilis) and Typhoon 0605 (Kaemi)) in the early phase of intrusion, the enhanced southwesterly leads to exceptional enhancement of the onshore flow; i.e., enhanced upwelling. Afterward, irrespective of the forced ocean responses resulting from the stronger local winds (Typhoon 0604) or the moderate typhoon-induced inertial oscillations (Typhoon 0605), the situation is not conducive to sustaining a stable, persistent upwelling system. On the other hand, when there is typhoon intrusion south of the upwelling system (e.g. Typhoon 0606 (Prapiroon)), the favorable southwesterly tends to be substituted by an anomalous northeasterly, which destroys the traditional coastal upwelling pattern. However, the canonical upwelling system tends to recover within 1-2 days of the typhoon passing.
