Study of tropical cyclone motion with a coupled hurricane-ocean model

The physical mechanism of baroclinic tropical cyclone (TC) motion is studied through use of a high resolution model. The effect of hurricane-ocean interaction is incorporated by coupling the atmospheric model to an intermediate ocean model, which can produce the major features caused by the hurricane-ocean interaction, including cooling, deepening and the induced currents of the ocean mixed layer.; In order to understand the roles of various physical processes in TC motion, a dynamical framework for study of baroclinic TC motion is proposed. A TC is treated as a positive potential vorticity (PV) anomaly from the environment. In this framework, the TC moves to the region with maximum tendency of the wave-number-one PV component. Therefore, TC motion is directly linked to the axially asymmetric PV tendency. Based on this new framework, a PV tendency diagnostic approach is developed. The new approach is capable of estimating TC speed and determining the fractional contributions of individual physical processes to the vortex motion with a suitable accuracy.; With this diagnostic approach, baroclinic TC motion is investigated by superposing an initial baroclinic vortex in different environments. It is found that diabatic heating can significantly affect the TC motion, which is indicated in the track, the mechanism of vertical coupling and the dominant physical processes that determine the TC motion. Without diabatic heating, the vortex motion at a certain level is dominated by the advection of the symmetric PV component by the asymmetric flow (steering) and the advection of the wave-number-one PV component by the cyclonic symmetric flow (AASF). In this case, the penetration flow alone cannot account for the vertical coupling. The AASF and vertical PV advection play an important role. Both processes are associated with the asymmetric vertical circulation. In the presence of diabatic heating, the vortex motion is dominated by the steering and the influence of diabatic heating. The diabatic heating affects the vortex motion by deflecting the vortex to the region with maximum vertically differential asymmetric diabatic heating. The vertical coupling is primarily implemented by the influence of diabatic heating. During the TC motion, the shear of the asymmetric flow and the asymmetric diabatic heating reach a quasi-equilibrium state through a very quick adjustment. Once the vertical shear of the asymmetric flow appears, a corresponding asymmetric diabatic heating field is induced in such a way that the maximum differential heating is located upstream of the relative flow.; Two types of track differences between the coupled and non-coupled experiments in the previous studies are obtained in two numerical experiments with the different initial SSTs. The track difference arises from the changes in the direct influence of the diabatic heating and its indirect influence indicated by the induced horizontal PV advection.