THE NONLINEAR PROPAGATION OF GRAVITY WAVE PACKETS IN A NONISOTHERMAL AND COMPRESSIBLE ATMOSPHERE
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摘要: 本文采用二维全隐欧拉(HCE)格式对具有高斯分布的重力波波包在非等温、可压大气中的非线性传播过程进行数值模拟.将数值计算结果与重力波在等温大气中的传播过程以及在WKB近似条件下的线性重力波理论进行了定量比较.分析结果表明:尽管受非线性作用与背景温场非均匀性的共同影响,在垂直方向上,重力波等相面向下运动,波包整体向上传播.由于非均匀背景温场的影响,在整个传播过程中,波包的形状变化比在等温大气中传播时显著得多,并且在波包的下游出现了波破碎.重力波波包的能量传播路径与WKB近似条件下的线性射线理论的结果差异很大,说明用WKB近似条件下的线性重力波理论来定量描述重力波的传播过程有一定的局限性.Abstract: By using two-dimentional Full-Implicit-Continuous-Eulerian(FICE)scheme,a numerical simulation of nonlinear propagation of a Gaussian gravity-wave-packet in the compressible and nonisothermal atmosphere is carried out,and a quantitative comparison with the propagation in an isothermal atmosphere and the linear gravity wave theory under the WKB approximation is also presented.The numerical analysis shows that for an initially given upgoing gravity-wave-packet although affected by the nonlinear interaction and the inhomogeneity of background temperature, during the propagation, the whole wave packet and the wave-associated energy keep moving upward,while the wave front moving downward. Affected by the inhomogeneity of the background temperature, the shape of the wave packet alters more significantly than in isothermal case, and there occurs wave breaking at the downstream region of the wave packet. The nonlinear energy propagation path of the gravity-wave-packet shows evident difference from the ray path derived from the linear ray theory under the WKB approximation,this indicates that it is not feasible to describe quantitatively the nonlinear propagation of gravity-wave-packet in a nonisothermal atmosphere by using the linear gravity wave theory under the WKB approximation.
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Key words:
- Gravity wave packets /
- Nonlinear propagation /
- Wave-associated energy
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