ESTIMATES OF KINETIC-ENERGY DISSIPATION UNDER BREAKING WAVES

The dissipation of kinetic energy at the surface of natural water bodi es has important consequences for many physical and biochemical proces ses including wave dynamics, gas transfer, mixing of nutrients and pol lutants, and photosynthetic efficiency of plankton. Measurements of di ssipation close to the surface obtained in a large lake under conditio ns of strong wind forcing are presented that show a layer of enhanced dissipation exceeding wall layer values by one or two orders of magnit ude. The authors propose a scaling for the rate of dissipation based o n wind and wave parameters, and conclude that the dissipation rate und er breaking waves depends on depth, to varying degrees, in three stage s. Very near the surface, within one significant height, the dissipati on rate is high (an order of magnitude greater than that predicted by wall layer theory) and roughly constant. Below this is an intermediate region where the dissipation decays as z(-2). The thickness of this l ayer (relative to the significant wave height) is proportional to the energy flux from breaking normalized by rho u(3), which for young wav es is proportional to wave age. At sufficient depth the dissipation ra te asymptotes to values commensurate with a traditional wall layer. Th e total energy flux into the water column can be an order of magnitude greater than the conventional estimate of rho u(3)/2 and depends str ongly on wave age. These results imply a pronounced shift in our appro ach to estimating kinetic energy dissipation in wave-stirred regions a nd in the modeling of various physical, chemical, and biological proce sses.