Analytical and Numerical Studies of the Beta-Effect in Tropical Cyclone Motion. Part I: Zero Mean Flow

The β-effect on tropical cyclone motion is studied using an analytical as well as a numerical model in a nondivergent barotropic framework. The analytical model and the linear version of the numerical model give essentially the same result: the linear β-effect causes a westward stretching of the model vortex but no significant movement of the vortex center. An east-west asymmetry in the meridional wind field is also created. It is the inclusion of the nonlinear term that produces the northwestward movement of the vortex previously found by other investigators (e.g., Kitade, 1981). This northwestward movement increases with both the maximum wind speed and the radius of maximum wind in a constant-shape vortex. A wind maximum is also found to the northeast of the vortex, which appears to be consistent with the observational findings of Shea and Gray. This asymmetry plays an important role in the vortex motion.