湍流和分子扩散对大气重力波翻转时间影响的模拟研究

重力波翻转意味着对流不稳定并伴随有非线性的波流相互作用,这是重力波改变背景大气结构的重要途径之一.利用自主建立的模拟重力波非线性传播过程的二维数值模式,研究了重力波的翻转时间(重力波发生对流不稳定时的持续时间)对湍流和分子扩散的依赖关系.模拟结果表明,翻转时间随着湍流扩散系数的增加而减小.通过与三维数值模式模拟的重力波翻转时间进行比较,适当调整湍流扩散系数,使得从二维模式得到的翻转时间与从三维模型得到的翻转时间具有可比性,从而得到湍流扩散系数的最优值.分子扩散从低热层开始,以指数形式增大,从而能够有效地耗散掉小尺度波动并使得重力波能够更快地恢复到稳定状态.

Simulation study on the overturning time of atmospheric gravity wave to the eddy and molecular diffusion

We studied the dependence of gravity waves(GWs)overturning and breaking on the eddy and molecular diffusions in a two dimensional(2D)fully nonlinear numerical model.Our numerical experiments show that the GW overturning time(defined as the time interval during which GW is convectively unstable)decreases with increasing eddy diffusion coefficient.By comparing to GWs overturning time simulated in previous 3D models,we obtain an optimal value of eddy diffusion coefficient that parameterizes the 3D breaking process,so that the overturning time from the 2D model is comparable to that from 3D models.The inclusion of molecular diffusion effectively dissipates small-scale structures during wave breaking and restores stability more quickly in the region above 110 km,where molecular diffusion becomes significant.