Numerical Simulation of Changes in Tropical Cyclone Intensity Using a Coupled Air-Sea Model

A coupled air-sea model for tropical cyclones (TCs) is constructed by coupling the Pennsylvania State University/National Center for Atmospheric Research mesoscale model (MM5) with the Princeton Ocean Model. Four numerical simulations of tropical cyclone development have been conducted using different configurations of the coupled model on the f-plane. When coupled processes are excluded, a weak initial vortex spins up into a mature symmetric TC that strongly resembles those observed and simulated in prior research. The coupled model reproduces the reduction in sea temperature induced by the TC reasonably well, as well as changes in the minimum central pressure of the TC that result from negative atmosphere-ocean feedbacks. Asymmetric structures are successfully simulated under conditions of uniform environmental flow. The coupled ocean-atmosphere model is suitable for simulating air-sea interactions under TC conditions. The effects of the ocean on the track of the TC and changes in its intensity under uniform environmental flow are also investigated. TC intensity responds nonlinearly to sea surface temperature (SST). The TC intensification rate becomes smaller once the SST exceeds a certain threshold. Oceanic stratification also influences TC intensity, with stronger stratification responsible for a larger decrease in intensity. The value of oceanic enthalpy is small when the ocean is weakly stratified and large when the ocean is strongly stratified, demonstrating that the oceanic influence on TC intensity results not only from SST distributions but also from stratification. Air-sea interaction has only a slight influence on TC movement in this model.