Influence of Tropical Cyclones on the Statistical Properties of Extreme Waves in the Tropical Indian Ocean

Abstract

In this MSc thesis, the climatology of ocean surface waves in the tropical Indian Ocean is investigated. Specific focus is on the probability distributions of the significant wave height, i.e. the mean height of the 1/3 of the waves over a 10-30 minutes interval, and of the mean wave period. Additionally, the characteristics of extreme waves, with heights that occur only once in e.g. 20 years or 50 years and which are generated by tropical cyclones, are analysed.

For this, experiments were conducted with the spectral wave model SWAN, which is forced by winds that are partly based on data from the ECMWF atmospheric model. The resolution of these wind data is too coarse to properly account for tropical cyclones. The new aspect of this study is that the winds were locally adjusted for the presence of tropical cyclones by including a sub-grid model in which wind speeds of the cyclones are computed from atmospheric pressure data.

It is shown that a 16-year simulation of the SWAN model, forced by winds from the ECMWF model and corrected for the presence of tropical cyclones by means of the sub-grid model, yields a wave climate and statistics of extreme waves that agree with those observed at some buoys. They also agree with output of a high resolution atmosphere-ocean wave model, which is much more expensive than the present model. Also, in depth analyses and interpretations of the results are given.