非线性内波通过参量亚谐波不稳定性的穿透
We present the results of a laboratory experimental study of an internal wavefield generated by harmonic, spatially periodic boundary forcing from above of adensity stratification comprising a strongly stratified, thin upper layer sitting atopa weakly stratified, deep lower layer. In linear regimes, the energy flux associatedwith relatively high frequency internal waves excited in the upper layer is preventedfrom entering the lower layer by virtue of evanescent decay of the wave field. Inthe experiments, however, we find that the development of parametric subharmonicinstability in the upper layer transfers energy from the forced primary wave into a pairof subharmonic daughter waves, each capable of penetrating the weakly stratifiedlower layer. We find that around 10% of the primary wave energy flux penetratesinto the lower layer via this nonlinear wave-wave interaction for the regime westudy.