Experimental Source Terms for Spectral Wave Forecast Models

A field experimental study of the spectral balance of the source terms for wind-generated waves in finite-depth water was carried out in Lake George, Australia. The measurements were made from a shore-connected platform at varying water depths from 1.2 m down to 20 cm. Wind conditions and the geometry of the lake were such that fetch-limited conditions with fetches ranging from approximately 10 km down to 1 km prevailed. The resulting waves were intermediate-depth wind waves with inverse wave ages, measured by the ratio of wind speed to the speed of the dominant (spectral peak) waves, in the range of 8 / 1 10 < < p c U . The atmospheric input, whitecap dissipation and bottom friction were measured directly and synchronously by an integrated measurement system. In addition, simultaneous data defining the directional wave spectrum, atmospheric boundary-layer profile and atmospheric turbulence were available. The observations were conducted over a three-year period from September, 1997 to August, 2000. Results revealed new physical mechanisms in the processes of spectral dissipation of wave energy and small-scale air-sea interaction. New parameterisations of the wind energy input and wave energy dissipation are suggested. They are presented in forms suitable for spectral wave models. The new features of the source functions are particularly relevant when modelling the steep wave/ strong wind conditions. Energy balance of the source functions was verified by means of independent redundant checks. Results of implementation of the new source functions in a research spectral wave model will also be presented.