风垂直切变对大气静力适应过程的影响——第一部分:波动响应

本文基于描述可压缩大气静力适应过程的线性模型,分别采用正交模法和WKBJ法,从波动响应的角度研究了风垂直切变对大气静力适应过程的影响.结合实际天气现象构造了四种风垂直切变模型,分别为垂直无切变的定常模型、类似锋面特征的线性切变模型、表征东风急流的反气旋式切变模型和类似西风急流的气旋式切变模型.分析了相应模型下静力适应过程中的波动特征及波能量演变规律.得到结论:(1)在定常模型中,破坏静力平衡的能量激发出四支两两成对的、传播性质类似声波和重力波的波动,波动能量在闭合系统假设下为守恒量;(2)风切变的存在改变了波动及其能量的传播特征,也改变了波动能量的守恒性;(3)在大气稳定层结下,若波动多普勒频率大于0且小于0.7倍的浮力振荡频率,则发展(衰亡)型波动的螺旋结构分别为:(a)在线性切变模型中,等相位线自下而上需向西(东)倾斜;(b)在反气旋式切变模型中,等相位线在急流轴上层自下而上需向西(东)倾斜,在急流轴下层自下而上需向东(西)倾斜;(c)在气旋式切变模型中,等相位线在急流轴上层自下而上需向东(西)倾斜,在急流轴下层自下而上需向西(东)倾斜;若波动多普勒频率大于0.7倍的浮力振荡频率,则情形相反.

Effects of Vertical Wind Shear (VWS) on hydrostatic adjustment-part I: wave response

Based on a linear model of a compressible, stably stratified atmosphere, the effects of Vertical Wind Shear (VWS) on hydrostatic adjustment is investigated by using the normal mode and WKBJ methods in the perspective of wave response. Four different vertical distribution models of the horizontal basic flow are considered according to the characteristics of atmosphere, respectively, which are constant model (mod_a) as a reference, linear model (mod_b) similar to the frontal system, anticyclone model (mod_c) representing the easterly jet and cyclone model (mod_d) simulating the westerly jet. Then the response characteristics of acoustic-gravity wave and evolution laws of wave energy are analyzed. Results show that for the constant model, two pairs of acoustic-gravity waves are generated by the energy which breaks the static equilibrium and wave energy is conserved with the hypothesis of closed system. The propagation characteristics of acoustic-gravity are changed due to the effects of VWS, the same as wave energy. With the change of VWS models, the evolutions of waves are compared. When the Doppler frequency is greater than zero and less than 0.7 times the buoyancy frequency, for whole layers in the linear model, for layers above jet axis in the anticyclone model and for layers below jet axis in the cyclone model, a gradually developed (decayed) spatial structure of the waves requires to meet the condition: the contours of phase westward (eastward) tilt from the bottom-up view and vice versa. When the Doppler frequency is greater than 0.7 times the buoyancy frequency, an opposite situation of wave evolution appears instead.