Wave model (WAM)

ECMWF uses and develops the WAve Model (WAM) model. It is coupled to the atmospheric model IFS/OpenIFS.

Since 1998 ECMWF has been running a coupled forecasting system where the atmospheric component of the Integrated Forecasting System (IFS) communicates with the wave model (WAM) through exchange of the Charnock parameter which determines the roughness of the sea surface (Janssen, 2004).

Our wave prediction system is based on a statistical description of oceans waves (i.e. ensemble average of individual waves). The sea state is described by the two-dimensional wave spectrum which gives the distribution of wave variance over different frequencies and propagation directions. Wave energy then follows from the product of water density, acceleration of gravity and wave variance.

The evolution of the wave spectrum follows from the energy balance equation which is explicitly solved by the WAM model. It determines the rate of change of the wave spectrum by adiabatic processes such as advection  and refraction of wave energy, and by physical mechanism such as wind-wave generation, nonlinear four-wave interactions, and dissipation of energy by processes such as wave breaking, micro-scale breaking and bottom dissipation.

Reference

Janssen, P.A.E.M. (2004),The interaction of ocean waves and wind, Cambridge University Press