We asked her to tell us about her thesis with the title Assessing and Reducing the Uncertainty in Regional Wave and Coupled Wave-Atmosphere Models during Extreme Events:
My dissertation is on assessing and reducing the uncertainty in regional wave and coupled wave-atmosphere models during extreme events. For the safety of humans at sea a reliable wind and wave forecast are essential. Especially, for an efficient route planning avoiding heavy weather but also minimising fuel consumption, precise wind and wave information are needed. Also for the sectors of offshore energy to plan and maintain their sites as well as for the coastal protection accurate wind and wave information with low uncertainties are wanted. However, due to uncertainties in initial conditions and necessary approximations made in the models, wind and wave forecasts become less accurate during extreme events. Hence, I looked at possibilities to reduce the uncertainty in atmospheric and wave models during extreme events.
Possible paths of reducing the uncertainties during extreme events found in my dissertation are on the one hand, high-quality and high temporal resolved wind fields for the regional wave model. On the other hand, the coupling between the wave and atmosphere model reduces the uncertainty in both models and enhances the accordance with observational data.
High-quality and high temporal resolved wind fields are needed for the regional wave model in the North and Baltic Seas in order to depict the extreme events in accordance with observations. When the temporal resolution is too low, i.e. six hourly, the peak in wind speed can be missed, which leads to an underestimation of the extreme event in the wave model. Hourly wind input data proved to be useful in order to give the wave model the chance to depict extreme events correctly.
A strong tool to reduce the uncertainty in both the atmospheric as well as the wave model is the coupling between them. In coupled simulations the roughness over the ocean can be estimated using wave parameters instead of depending on the wind only. The use of wave depended roughness length leads to significant changes in the roughness length itself, as well as the wind speed, the mean sea level pressure and the significant wave height. Due to an increased roughness, the wind speed, the pressure gradient and the significant wave height are reduced. The largest changes in wind speed and significant wave height occur during extreme events. These changes proved to be larger than the internal model variability, stemming for the uncertainty in initial conditions in the atmospheric model. Also, the accordance with observations can be enhanced, especially for high winds and large waves. Furthermore, the coupling reduces the internal model variability. Hence, the uncertainty in the model simulations is reduced when using the coupled system compared to the stand-alone atmospheric model. Therefore, the use of coupled systems proved to be useful to reduce the uncertainty in wind and wave information from atmospheric and wave models. This reduction in uncertainty in wind and wave forecast can be beneficial for all activities conduced offshore as mentioned in the beginning.