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

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.