重力波波包在真实大气中传播特性的数值研究

采用二维全隐欧拉（FICE）格式，对重力波波包在真实大气中的非线性传播和演变过程进行了数值模拟，模拟结果表明，在中层大气下部激发的向上传播的重力波波包在传播到中层顶之前，波相关能量沿着射线路径传播，非线性效应和背景温场对波能量传播路径的影响很小，当波包传播到低热层大气后，波包饱和波相关能量几乎完全沿着水平方向传播，垂直方向的能量传播受到抑制，这与在无耗大气下，WKB近似条件下的线性重力波理论的预言相差很大，深入的分析表明抑制重力波波包向上传输能量的关键因素是大气分子粘性的垂直非均匀性。非线性和背景温场的影响不足以完全抑制波能量的向上传播，此外，在波包的整个传播过程中，由于非线性，背景温度和背景耗散的共同作用，重力波波包的垂直波长随时间明显减小，这些结果说明大气的分子粘性特别是分子粘性的垂直不均匀性对重力波波包在中、高层大气的非线性传播过程起着重要作用。

A NUMERICAL STUDY ON THE PROPAGATION CHARACTERISTICS OF GRAVITY-WAVE PACKETS IN REAL ATMOSPHERE

By using a two-dimensional full-implicit-continuous-Euleri (FICE) scheme, the nonlinear propagation and evolution of gravity-wave packets in real atmosphere is simulated. The numerical resu1ts show that when an upgoing gravity-wave packet is generated in low mesosphere, it can propagate along its ray path before arriving at the height of mesopause, the nonlinearity and background atmospliere have little influence on its energy propagation path. However, when the wave packet arrives at low thermosphere, the wave packet and wave associated energy propagate almost horizontally, and its vertical propagation is halted. which departs obvious1y from the prediction of linear gravity-wave theory under WKB approximation in non- dissipative case. A further discussion indicates that it is the vertical inhomogeneity of molecular viscosity that causes the restriction of upward energy propagation of the gravity-wave packet. Moreover, during the whole propagation, affected by the joint actions of nonlinearity, background temperaturc and dissipation, the domi- nant vertical wavelength of the wave packet decreases obviously with time. These indicate that the molecular viscosity especially the vertical inhomogeneity of molec- ular viscosity plays an important role in the nonlinear propagation of gravity-wave packets.