风垂直切变对大气静力适应过程的影响——第三部分:能量转换

基于前两部分的研究,第三部分从能量转换的角度揭示了风垂直切变对大气静力适应过程的影响.研究显示,对非静态等温大气,初始时刻加以有效势能和有效弹性势能的强迫后,风垂直切变改变了适应过程中扰动能量在各能量形式中的分配比例,这种作用随扰动尺度和时间的变化有显著差异,系统尺度越小影响越显著.比较东风急流模型和西风急流模型显示,负的风切变应力使得四类扰动能量谱随系统尺度的变化趋于平缓,使得微尺度和小尺度(中尺度)系统中扰动垂直动能(扰动水平动能)的比例随时间减小,正的风切变使得扰动能量谱随系统尺度的变化显现跳跃的特征,使得中尺度(微尺度和小尺度)系统中扰动垂直动能(扰动水平动能)的比例随时间减小.风垂直切变引起的动量通量输送是扰动能量与基本气流能量之间交换的通道,当风切变应力和动量输送方向相同时,风垂直切变使得能量向基本态转移,维持基本气流,削弱扰动能量,缩短静力适应过程的周期;当风切变应力和动量输送方向相反时,风垂直切变作用相反;此作用随着扰动尺度的变化差异明显.

Effects of Vertical Wind Shear (VWS) on hydrostatic adjustment-Part III: energy partitioning

Continuing our previous studies, this paper reveals the effects of Vertical Wind Shear (VWS) on the hydrostatic adjustment from the perspective of energy partitioning. The wind vertical shear changes the proportion of the perturbation energy in each energy form during the hydrostatic adjustment for a non-resting isothermal atmosphere with the initial perturbation of available potential energy and available elastic energy. This effect is significantly different from the changes of perturbation scale and time, and the smaller the system scale is, the more obvious the effect is. The proportions of kinetic, available potential, available elastic and steady state energy are significantly affected by the four different VWS models. The negative (positive) VWS makes the four kinds of perturbation energy spectrum gradually stabilized (oscillated) with the change of the system scale. The hydrostatic adjustment is a process of energy re-partitioning; the conversion between available elastic energy which plays the role of energy hub station and vertical kinetic energy represents the process of hydrostatic adjustment. The transport of momentum flux caused by the VWS is the exchange channel between the perturbation energy and the steady state energy. When the VWS stress points to the direction of momentum transport, the energy is transported from the perturbation state to the steady state, which maintains the basic flow and weakens the perturbation energy, so that the period of the hydrostatic adjustment is reduced accordingly and vice versa.