摘要
通过一个二维非线性斜压Eady波模式 ,讨论了斜压系统中初始扰动快速发展的动力学机制。由于斜压切变气流存在 ,其对扰动位涡的平流作用可引起初始扰动位涡的“位涡非屏蔽” (potentialvorticityunshielding) ,导致线性系统初始扰动的快速增长。摩擦作用主要通过耗散局地扰动位涡 ,改变扰动位涡异常结构 ,特别是水平方向的位涡异常分布 ,从而减弱初始扰动位涡的“位涡非屏蔽”作用 ,抑制系统初始扰动动能的快速增长。非线性作用可以抑制较大振幅扰动的增长 ,同时引起扰动位涡异常丰富的垂直结构产生 ,导致初始扰动位涡的“位涡非屏蔽”的减弱 ,从而抑制初始扰动的快速增长。不同的初始扰动结构 ,可以产生不同的扰动位涡异常结构 ,相应存在不同的“位涡非屏蔽”作用 ,导致初始扰动的快速增长过程不同。位涡异常水平结构为“正负正”或“负正负”分布时 ,有利于初始扰动的快速增长 ,而上下层异号的扰动位涡异常在垂直方向间隔的距离越大 ,越有利于初始扰动的快速发展 ,这些结果进一步深化了对“位涡非屏蔽”的理解。
A two-dimensional nonlinear baroclinic Eady wave model is used to study the dynamical mechanisms for the rapid growth of initial balanced perturbations in the baroclinic system. The advection effect of baroclinic shear flow on perturbation potential vorticity leads to the “potential vorticity unshielding” of initial perturbation potential vorticity (PV), which induces the rapid growth of initial perturbations in the linear system. Due to dissipating the local perturbation PV, friction modifies the structures, especially the horizontal distribution, of PV anomalies, accordingly weakens PV unshielding of initial perturbation PV so as to restrain the transient growth of initial perturbation kinetic energy. Nonlinear effect induces the rich vertical structures of perturbation PV anomalies, which weakens PV unshielding of initial perturbation PV, consequently restrain the rapid growth of initial perturbations with large amplitude. Different structures of initial perturbations may cause different structures of perturbation PV anomalies, as well as different PV unshielding which leads to the different rapid growth process of initial perturbations. The “negative-positive-negative” or “positive-negative-positive” distribution in the horizontal structure for PV anomalies is favourable for the rapid growth of initial perturbations. While the farther the vertical distance of opposite potential vorticity anomalies is, the more favorable it is for the rapid growth of initial perturbations. These results provide some new sights for PV unshielding.
出处
《大气科学》
CSCD
北大核心
2004年第6期847-863,共17页
Chinese Journal of Atmospheric Sciences
基金
国家自然科学基金资助项目 40 3 2 5 0 1 4
40 0 75 0 1 0
40 0 2 85 0 4
高等学校优秀青年教师教学科研奖励计划TRAPOYT共同资助
