Influence of Wave-current Interaction, and High Frequency Forcing upon Storm Induced Currents and Elevations

Abstract

A high resolution (of order 1km grid) three dimensional model of the Eastern Irish Sea, including wave-current interaction effects, is used to examine the surges of November 1977. Computed surge elevations and currents are compared with observations taken at the time. The inclusion of wave-current interaction effects, in which the amplitude of the surface wind-wave field changes over the period of the storm, is shown to influence computed surge elevations in shallow regions. The inclusion of wave-current interaction effects also influences currents, particularly in the near bed region. An increase in air-sea drag coefficient, reflecting an enhanced sea surface roughness due to increased wave heights at the time of the storm, is shown to improve the computed storm surge elevation in shallow regions.The effects of including a high frequency component (based on observations) into the lower frequency meteorological forcing usually used to drive the model, is examined. Such fluctuations produce high frequency variations in the near surface currents, however such changes are not found at depth. The introduction of similar high frequency changes into the currents along the open boundary of the model is also considered. This produces high frequency variations throughout the water column, within the interior of the Eastern Irish Sea, which are similar to those found in the observations.