A Mediterranean Sea Wave Spectral Model

Abstract

ABSTRACT An operational Mediterranean wave spectral model has been developed through the cooperative efforts of the U. S. Naval Oceanographic Office (NAVOCEANO), Fleet Numerical Weather Central (FNWC) and New York University (NYU). Since April, 1972, the model has been operating in a real-time environment (analyses/prognoses to 48 hours). The model is a modified version of the original NYU North Atlantic wave model and has two main parts:wave energy growth based on a modified version of the Miles Phillips growth mechanism and dissipation at individual grid points andwave energy propagation from grid point to grid point. 'The Mediterranean wave model uses a conic conformal grid, permitting the assumption of equal spacing between grid points. There are 455 sea points with a mesh length of 67 km. The wave model driving force is a modified version of the FNWC marine wind model that has a mesh length of approximately 370 km. For use in the Mediterranean, the winds are interpolatec between marine wind field grid points. At analysis/preanalysis times, wind reports from synoptic ship files are reanalyzed in the Mediterranean wind program so that local wind phenomena, such as mistrals, are included in the wind field. The Mediterranean wind and wave model was evaluated with ship reports, one wave buoy and an airborne wave laser. The wave computations appear to be as good as the wind input allows. The on-time analyses and 24-hour forecasts of wave heights are transmitted to Fleet Weather Central, Rota, Spain. INTRODUCTION A Mediterranean wave spectral model has been developed through the cooperative efforts of the U. S. Naval Oceanographic Office (NAVOCEANO), Fleet Numerical Weather Central (FNWC) and New York University (NYU). Since April, 1972, the model has been operating in a real-time environment (analyses/prognoses to 48 hours). The Mediterranean wave spectral model is a modified version of the original NYU North Atlantic wave model and has two main parts:wave energy growth and dissipation at individual grid points andwave energy propagation from grid point to grid point. WAVE SPECTRAL MODEL The growth of wave energy in this model is accomplished with an equation that combines modified versions of the Miles instability theory and. Phillips resonance mechanism. 2 The model evaluates all computed spectra to ensure that the calculations never exceed the limits of the Pierson-Moskowitz4 fully developed spectrum for the given wind speed. For computational purposes, the energy spectra are broken into matrices of 15 frequency bands by 12 directional bands as shown in Table 1. The energy in all the frequency bands except the highest frequency band are propagated through the grid system by a "jump" technique.