重力波波包在剪切风场中的非线性传播

THE NONLINEAR PROPAGATION OF GRAVITYWAVE PACKETS IN THE SHEARED AMBIENT

采用二维全隐欧拉（ＦＩＣＥ）格式，对具有高斯分布的重力波波包在剪切风场中的非线性传播过程进行数值模拟和分析．数值分析结果表明：在没有出现临界展的情况下，尽管存在非线性效应，在整个传播过程中，波动的等相面向下运动，波包和波相关能量仍然能够自由地向上传输、波相关扰动速度随高度增加而增加，并且垂直波长随高度增加而减小．模拟结果表明在剪切风场中传播的重力波波包，其传播特性本质上仍然遵循线性重力波理论．

By using a two-dimentional Full- Implicit- Continucus- Eulerian (FI C E ) scheme,a numerical simulation of nonlinear propagation of a Gaussian gravity-wave-packetin sheared ambient is carried out. The numerical analysis shows that for an initiallygiven upgoing gravity-wave-packet, in absence of a critical layer, although there exists nonlinear interaction during the propagation, the whole wave packet and thewave-associated energy keep moving upward, while the wave front moving downward. Wave-associated perturbation velocity increases with the increasing height,and the vertical wavelength decreases with the increasing height. The propagationpath of wave energy flux coincides well with the ray path predicted by the lineargravity wave theory, but the magnitude of wave energy propagation velocity is evidently smaller than the group velocity derived from the linear gravity wave theory.This indicates that the nonlinear propagation characteristics of gravity wave packetsin sheared ambient are essentially linear.