A parameterization for the correction of ERA5 severe winds for extreme ocean wave modelling
Ahmed I. Elshinnawy, Melisa Menéndez, Raúl Medina
Abstract
Atmospheric re-analyses are frequently used to force spectral wave models to develop long-term wave datasets. The accuracy of marine surface winds significantly affects the reliability of the modelled wave fields, especially under wave storm conditions. In this study, we employ the spectral wind-wave model WAVEWATCH III (WW3) forced by ERA5 winds to assess their reliability in modelling extreme ocean waves. A one-year wave hindcast of 2010 is simulated and validated against measurements from both in-situ buoy and altimeter data. The results indicate that ERA5 winds underestimate extreme wave conditions for significant wave heights ( H s ) larger than 7.5 m. Accordingly, we present a new wind parameterization, in WW3, that corrects the wind speed bias of ERA5. It has a sigmoid mathematical form showing an exponential growth with a bounded limit of the maximum wind speed to be corrected. The results show that the newly proposed parameterization corrects the negative biases for H s between 7.5 m and 14 m when compared with the wave measurements. The biases are reduced from −0.15 m to negligible values in most of the ocean basins. Other hindcast years were also simulated with WW3 using the new parameterization and the outputs were validated against altimeter data, showing reliable results. This confirms the utility of the new parameterization for extreme ocean wave modelling, which is useful for wide offshore and ocean engineering applications. • The reliability of ERA5 wind fields in modelling extreme ocean waves is assessed. • Negative biases are obtained when modelling extreme waves with H s values exceeding 7.5 m when using ERA5 raw winds. • A parameterization is developed for WAVEWATCH III for bias correction of ERA5 wind speeds to properly model stormy waves. • Wind correction parameters led to negligible biases for the range of H s =7.5-14 m when compared with wave measurements. • The biases were reduced from −0.15 m to negligible values (∼-0.05 m) in the Atlantic Ocean.