Nonlinear internal waves on the continental shelf

Graduation date: 2010The properties and evolution of nonlinear internal waves (NLIWs) depend\ud upon the background conditions within which waves form, propagate, and dissipate. As a result, the NLIW field on the New Jersey shelf displayed dramatic variability during the Shallow Water 2006 experiment. Wave variability was exhibited by 1) amplitudes that ranged from 5 m to over 20 m, 2) irregular wave arrival times, and 3) wave forms that were either mode-1 or mode-2 in vertical structure. Over the month-long experiment, a six-day time span, which was coincident with the neap tide, was distinguished by having the largest observed NLIWs. The change in\ud character of the observed waves between this period and the remainder of the month resulted in wave energies that increased by a factor of 5-10. The wave energy budget also varied spatially, as waves propagated across the shelf. On the outer shelf, energy was supplied to the NLIWs by the internal tide; and, inshore the balance shifted so that the change in energy per unit time was balanced by dissipative loss in the waves. While at a particular location dissipation in the core of the waves had only a weak dependence on energy, the average dissipative loss scaled with the maximum energy of the waves. NLIW dissipation was dominated by shear-driven turbulence in the mixed layer; at the pycnocline depth, NLIW dissipation was on average 10 times larger than that observed in background profiles. Consequently, the passage of NLIWs resulted in large heat fluxes across the pycnocline, contributing as much as 50% to the total average heat flux on the shelf. These changes in energetics were accompanied by structural changes in the wave form, including changes induced by wave interactions and the polarity reversal of three large-amplitude wave groups