Numerical Study of Interactions between surface waves, currents and hydrography in extreme weather conditions

Abstract

Surface gravity waves significantly affect air-sea interactions, turbulent vertical mixing, ocean currents and hydrography in the upper ocean, particularly during extreme weather events such as hurricanes and winter storms. Currents in the upper ocean also influence surface waves via the Doppler shift, relative wind effect, refraction and advection. This thesis examines the impact of wave breaking (WB), Langmuir turbulence (LT) and conservative wave effects on the upper ocean dynamics and effects of currents on surface waves during hurricane conditions using a coupled circulation-wave model. The wave-current interactions (WCIs) are investigated numerically in two cases using (a) idealized hurricanes moving at three translational speeds and (b) Hurricane Arthur (2014) over the northwest Atlantic Ocean. Model results in the fully coupled run are examined in comparison with results in other runs in which wave effects are selectively disabled to quantify main physical processes of WCIs, with a special focus on wave-induced changes to the upper ocean turbulent kinetic energy (TKE), thermal structure and currents. For the case of idealized hurricanes, analyses of model results reveal that LT has a larger impact on upper ocean currents, temperature and TKE, compared to the other considered processes. The combined wave effects reduce the surface currents in the front two quadrants of the hurricane and enhance the cold wake and near-surface cooling, predominantly to the right of the storm track. For the case of Hurricane Arthur, both the LT and WB driven acceleration are found to be important to storm-induced changes in the upper ocean temperature and circulation. By contrast, the WB induced surface flux of TKE has a limited effect on the temperature, salinity and currents in the surface layer. Over pathways of the Gulf Stream, the large WCIs reduce the significant wave heights (SWHs) of surface waves during Hurricane Arthur, with the biggest differences occurring to the right of the storm track. SWHs on the left hand side of the storm are limited by the shorter fetch, shallower water depths and coastline.