Improving wave forecasting in variable wind conditionsthe effect of resolution and growth rate for the catalan coast

Resumen

The main objective of this study is to improve wind wave forecasting in the NW Mediterranean Sea while focusing on the characteristic sharp gradients of the wind and wave conditions. This work was motivated by the limited accuracy of wave models in semi-enclosed-basins and orography-controlled wind conditions, especially during fetch-limited storm events. First, to reduce the commonly observed under-estimation of wave parameters, the mesoscale variability of wind and wave fields was characterized in time (1 h to 1 day) and in space (10 km to 100 km). Second, to better capture the typical sharp gradients, the grid size of the input wind fields was decreased during a characteristic storm event from 18 km to 4 km and the wind input frequency was increased from 6 h to 1 h. Third and last, the rate of wave growth in the numerical model was tuned in order to match the local rate of wave growth. The rate of non-dimensional growth in the region of study, which was calculated using measurements along the fetch, turned out to be faster than simulated using the default physical parameterizations and faster than reported in previous studies. Adjusting the wave growth rate in the model to the observations improved the estimated wave height about 18 % and the peak frequency about 4%. Decreasing the grid size of the numerical models from 12 km to 4 km improved the timing of the wave peaks but not the maximum values of the storm. Increasing the frequency of the wind input (from 6 h to 3 h) improved the estimation of the maximum wave height values (peaks) of the storm about 13%. Summarizing, the results of this work indicated that tackling wind and wave gradients in complex regions such as the study area it is posible to reduce the under-estimation of wave parameters and to improve wave forecasting.