摘要：
利用二维非静力数值模式,对海洋跃层中剪切背景流下内波做了线性和非线性模式的数值试验,结果表明:在本文所取的初始场和环境参数下,海洋内波密度扰动大值中心始终出现在密度跃层附近,被跃层所俘获,这与实际观测相一致;线性情况下,流函数扰动中心与密度扰动中心有很好地配合,密度扰动正、负中心附近分别存在流函数扰动的正、负单圈环流中心,且单圈环流垂直贯穿整个水体.线性模式中内波扰动强度在调整适应期后一直呈指数增长发展,剪切背景流是不稳定的;而非线性情况则呈准线性增长发展,以后增长停止而进入稳定期,且后者的增长也比前者要慢;非线性效应抑制了内波增长而使之趋于稳定,具有维稳作用.随着积分时间增加,线性模型中内波波包波形基本不变.波包的负、正振幅大体相同,整个波包宽度也基本不变,仅振幅有所增长;内波波包传播速度与其振幅无关,且传播速度基本不变.非线性情况下内波波包的形状则发生改变,其负、正振幅之比越来越大,波峰前的陡降也越来越强;并且内波传播速度与其振幅和波形有关,通常非线性效应越强,内波传播越慢.从本文中海洋内波的波长、周期和传播速度来看,该内波属于高频内波(短周期内波),性质为内重力惯性波.%Numerical experiments of oceanic internal waves in pycnocline with background shear flow were conducted with two-dimensional non-hydrostatic linear and nonlinear numerical models.With the initial field and parameters prescribed by present study,it shows that he maximum density disturbance always ap-pears within pycnocline,or captured by the pycnocline,consistent with in situ observations.In linear model, the stream function coincides with the density disturbance,with its negative/positive center corresponding to negative/positive center of the density disturbance,which is vertically distributed from ocean surface to bottom.The intensity of internal waves in linear model grows exponentially after adj ustment period,and the background shear flow is unstable.But in nonlinear model,internal waves shows a quasi-linear develop-ment,then develop slowly till reaching a steady period.Thus the growing rate of internal waves in linear model is larger than that in nonlinear model,suggesting that the nonlinear effect reduces instability internal waves.As the integration of model continues,the shape of internal wave packet in the linear case is basically unchanged,except that the amplitude of internal waves increases.The propagation velocity of the wave packet is independent of its amplitude.But in nonlinear case,the shape of internal wave packet changes,and both its amplitude and the sudden fall before the wave crest increases consistently.The velocity of internal wave is related to its amplitude and wave shape,and the stronger nonlinear effect is,the more slowly the velocity of internal wave is.Based on the wave length,period and propagating velocity,the internal waves in the numerical experiments should be classified as high frequency inertial gravitational waves (or short-peri-od waves).
