The effect of baroclinicity on vortex axisymmetrization is examined within a two-layer dynamical model.Three basic state vortices are constructed with varying degrees of baroclinicity：（i） barotropic,（ii） weak bar...The effect of baroclinicity on vortex axisymmetrization is examined within a two-layer dynamical model.Three basic state vortices are constructed with varying degrees of baroclinicity：（i） barotropic,（ii） weak baroclinic,and （iii） strong baroclinic.The linear and nonlinear evolution of wavenumber-2 baroclinic disturbances are examined in each of the three basic state vortices.The results show that the radial propagating speed of the vortex Rossby wave at the lower level is larger with the stronger baroclinicity,resulting in a faster linear axisymmetrization process in the stronger baroclinic vortex.It is found that the nonlinear axisymmetrization process takes the longest time in the strongest baroclinic vortex among the three different basic vortices due to the weaker kinetic energy transfer from asymmetric to symmetric circulations at the lower level.A major finding in this study is that the same initial asymmetric perturbation can have different effects on symmetric vortices depending on the initial vortex baroclinicity.In numerical weather prediction models,this implies that there exists a sensitivity of the subsequent structural and intensity change solely due to the specification of the initial vertical shear of the tropical cyclone vortex.展开更多
The barotropic and baroclinic disturbances axisymmetrized by the barotropic basic vortex are examined in an idealized modeling framework consisting of two layers.Using a Wentzel-Kramers-Brillouin approach,the radial p...The barotropic and baroclinic disturbances axisymmetrized by the barotropic basic vortex are examined in an idealized modeling framework consisting of two layers.Using a Wentzel-Kramers-Brillouin approach,the radial propagation of a baroclinic disturbance is shown to be slower than a barotropic disturbance,resulting in a slower linear axisymmetrization for baroclinic disturbances.The slower-propagating baroclinic waves also cause more baroclinic asymmetric kinetic energy to be transferred directly to the barotropic symmetric vortex than from barotropic disturbances,resulting in a faster axisymmetrization process in the nonlinear baroclinic wave case than in the nonlinear barotropic wave case.展开更多
The dependence of tropical cyclone(TC) intensification on the Coriolis parameter was investigated in an idealized hurricane model. By specifying an initial balanced vortex on an f-plane, we observed faster TC developm...The dependence of tropical cyclone(TC) intensification on the Coriolis parameter was investigated in an idealized hurricane model. By specifying an initial balanced vortex on an f-plane, we observed faster TC development under lower planetary vorticity environment than under higher planetary vorticity environment. The diagnosis of the model outputs indicates that the distinctive evolution characteristics arise from the extent to which the boundary layer imbalance is formed and maintained in the presence of surface friction. Under lower planetary vorticity environment, stronger and deeper subgradient inflow develops due to Ekman pumping effect, which leads to greater boundary layer moisture convergence and condensational heating. The strengthened heating further accelerates the inflow by lowing central pressure further. This positive feedback loop eventually leads to distinctive evolution characteristics.The outer size(represented by the radius of gale-force wind) and the eye of the final TC state also depend on the Coriolis parameter. The TC tends to have larger(smaller) outer size and eye under higher(lower) planetary vorticity environment. Whereas the radius of maximum wind or the eye size in the current setting is primarily determined by inertial stability, the TC outer size is mainly controlled by environmental absolute angular momentum.展开更多
基金supported by ONR Grants N000140310739 and PE 0602435Npartially sponsored by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
文摘The effect of baroclinicity on vortex axisymmetrization is examined within a two-layer dynamical model.Three basic state vortices are constructed with varying degrees of baroclinicity：（i） barotropic,（ii） weak baroclinic,and （iii） strong baroclinic.The linear and nonlinear evolution of wavenumber-2 baroclinic disturbances are examined in each of the three basic state vortices.The results show that the radial propagating speed of the vortex Rossby wave at the lower level is larger with the stronger baroclinicity,resulting in a faster linear axisymmetrization process in the stronger baroclinic vortex.It is found that the nonlinear axisymmetrization process takes the longest time in the strongest baroclinic vortex among the three different basic vortices due to the weaker kinetic energy transfer from asymmetric to symmetric circulations at the lower level.A major finding in this study is that the same initial asymmetric perturbation can have different effects on symmetric vortices depending on the initial vortex baroclinicity.In numerical weather prediction models,this implies that there exists a sensitivity of the subsequent structural and intensity change solely due to the specification of the initial vertical shear of the tropical cyclone vortex.
基金sponsored by ONR Grants PE 0602435N and N000140310739partially supported by the Japan Agency for Marine-Earth Science and Technology
文摘The barotropic and baroclinic disturbances axisymmetrized by the barotropic basic vortex are examined in an idealized modeling framework consisting of two layers.Using a Wentzel-Kramers-Brillouin approach,the radial propagation of a baroclinic disturbance is shown to be slower than a barotropic disturbance,resulting in a slower linear axisymmetrization for baroclinic disturbances.The slower-propagating baroclinic waves also cause more baroclinic asymmetric kinetic energy to be transferred directly to the barotropic symmetric vortex than from barotropic disturbances,resulting in a faster axisymmetrization process in the nonlinear baroclinic wave case than in the nonlinear barotropic wave case.
文摘The dependence of tropical cyclone(TC) intensification on the Coriolis parameter was investigated in an idealized hurricane model. By specifying an initial balanced vortex on an f-plane, we observed faster TC development under lower planetary vorticity environment than under higher planetary vorticity environment. The diagnosis of the model outputs indicates that the distinctive evolution characteristics arise from the extent to which the boundary layer imbalance is formed and maintained in the presence of surface friction. Under lower planetary vorticity environment, stronger and deeper subgradient inflow develops due to Ekman pumping effect, which leads to greater boundary layer moisture convergence and condensational heating. The strengthened heating further accelerates the inflow by lowing central pressure further. This positive feedback loop eventually leads to distinctive evolution characteristics.The outer size(represented by the radius of gale-force wind) and the eye of the final TC state also depend on the Coriolis parameter. The TC tends to have larger(smaller) outer size and eye under higher(lower) planetary vorticity environment. Whereas the radius of maximum wind or the eye size in the current setting is primarily determined by inertial stability, the TC outer size is mainly controlled by environmental absolute angular momentum.
