Tropical cyclone intensity change from a simple ocean-atmosphere coupled model

The interaction between a tropical cyclone (TC) and the underlying ocean is investigated using an atmosphere-ocean coupled model. The atmospheric mode l is developed from the Pennsylvania State University (Penn State)-National Center for Atmospheric Research (NCAR) mesoscale model version 4 MM4 and t he ocean model consists of a mixed layer and an inactive stagnant layer ben eath. Coupling between the atmosphere and the ocean models is achieved thro ugh wind stress and surface heat and moisture fluxes that depend on the sea surface temperature (SST). In the absence of a background flow, the atmosp heric component consists of only a predefined vortex with an initial centra l pressure and the radius of the 15 m s(-1) wind. The basic control experim ents demonstrate that the coupled model can simulate the development of a T C and its interaction with the ocean. Changes in TC intensity are sensitive to those of SST and the response is a lmost instantaneous. An SST of similar to 27 degreesC is found to be the th reshold for TC development. In addition, the initial depth of the ocean mix ed layer has an appreciable effect on TC intensity, which also depends on t he movement of the TC. Furthermore, the vertical structure of ocean (vertic al temperature gradient in the stagnant layer and temperature differential between the two layers) plays a significant role in modulating TC intensity . In the presence of a warm core eddy (WCE), a TC intensifies before its cent er reaches the edge of the WCE. Although the TC attains maximum intensity a t the center of the WCE, it does not weaken to its original intensity after leaving the WCE. During the entire passage of the TC, the SST at the cente r of the WCE decreases by about only 1 degreesC, and the WCE generally main tains its original characteristics. However, two cold pools are observed ar ound its periphery. A similar intensification process occurs when a TC move s over a sharp SST gradient and a locally deep ocean mixed layer. These res ults are explained by the interaction between the ocean and the TC circulat ion as well as the change in the total surface heat flux.