Simulation of Ocean Responses to an Idealized Landfalling Tropical Cyclone Using a Coupled Atmosphere-Wave-Ocean Modeling System

Abstract

ABSTRACT Oceanic responses to a hypothetical landfalling tropical cyclone (TC) are studied by using a coupled atmosphere-wave-ocean modeling system (CAWOMS). A set of experiments are conducted to compare the effects of atmosphere-wave-ocean interaction on ocean responses in coastal and deep waters. The results show that in a three-way coupled atmosphere-wave-ocean system, the response to a tropical cyclone is considerably different in coastal water and deep water. In a three-way coupled system, air-sea interactions tend to increase coastal storm surge, inundation, significant wave heights and ocean currents in shallow coastal areas as a result of wave-enhanced air-sea heat and moisture fluxes. But the change is little in sea surface temperature and mixed-layer structure due to the well-mixed nature in the coastal zone. In contrast, in a three-way coupled system, air-sea interactions enhance sea surface cooling, increase mixed layer depth in deep waters largely due to the tendency of a wave-enhanced TC to induce strong mixing and entrainment in the upper ocean. A stronger TC also strengthens the surface currents and significant wave height in the offshore waters. The inclusion of waves in air-sea interactions fundamentally changes the dynamic and thermodynamic coupling between tropical cyclone and the underlying ocean. In the absence of TC-wave consideration, a negative feedback between the TC and the upper ocean mixed layer results in a weakening of the TC system and a cooling in the offshore upper ocean and therefore reduces coastal storm surge, flooding areas, significant wave height and ocean currents. Only in a TC-wave-ocean three-way coupled system, air-sea interaction may correspond to a stronger TC due to wave-induced air-sea heat and moisture fluxes which compensate the effect of negative feedback between the TC and the upper ocean. In coastal waters, the negative feedback between the TC and the ocean mixed layer is fairly weak. Air-sea interaction is dominated by the positive TC-wave feedback. As a result, air-sea interaction increases coastal storm surge, inundation, currents and significant wave height.