重力波波包在三维非等温大气和水平风场中非线性传播的数值研究

A NUMERICAL RESEARCH OF NONLINEAR PROPAGATION OF GRAVITY WAVE PACKETS IN THREE-DIMENSION NONISOTHERMAL ATMOSPHERE AND HORIZONTAL WINDS

采用全隐欧拉格式（FICE）对重力波波包在三维非等温大气、均匀和剪切风场中的非线性传播进行了数值模拟,给出了重力波波包三维非线性传播的全过程,分析了重力波的传播特性及背景温度场、风场对重力波传播的影响.结果表明:波包扰动速度振幅的增长比在WKB条件下振幅的增长要慢;波包非线性传播的路径、能量传输速度不同于WKB近似下的结果,非线性效应导致了重力波的传播特性的改变;温度场的非均匀性会改变重力波传播的路径和速度;剪切风场使扰动速度振幅的增加变得缓慢,使垂直波长减小.

A numerical simulation of nonlinear propagation of gravity wave packets with Gaussian distribution in a three-dimension nonisothermal atmosphere, homogeneous and sheared horizontal winds is presented in this paper. By using FICE scheme, the model solves the fully nonlinear, time dependent, three-dimensional fluid equations. The whole propagation process of the gravity wave packets are showed, the propagation characteristics of nonlinear propagation and the influence of background winds, temperature on gravity wave's propagation are analysed. Although there exits the nonlinearity, the basic characteristics of nonlinear propagation are in agreement with that of the linear propagation. During the propagation process, the phases of waves move downward, the wave packet and the wave-associated energy propagate upward and wave disturbed velocity increases with the height. The calculation results also show that wave disturbed velocity increases less than the results expected by WKB approximation. There is difference between the simulation calculations and the results given by WKB approximation on energy trace and group velocity. This indicates that the nonlinearity affects the characteristics of gravity waves. The inhomogeneous temperature lowers group velocity and changes the path of energy propagation. The sheared horizontal winds decreases range of horizontal disturbed velocity's amplitude and the vertical wavelength of gravity wave packet, the vertical wavelength reduces from 10km at altitude of 60km to 4km at altitude 83km. When propagating in the sheared winds, the mean vertical energy flux of gravity wave packet reduces with the height, this implies there is energy exchange between the background winds and gravity wave packet which leads to the coupling of different layers of atmosphere.