Vortex motion in relation to the absolute vorticity gradient of the vortex environment

Abstract

Abstract Recent attempts to establish a relationship between tropical cyclone motion and the absolute vorticity gradient of the cyclone environment are reviewed. Evidence is presented, both from analytic and numerical calculations, to show that for barotropic vortices there is no unique relationship between vortex motion, c. and the local absolute vorticity gradient of the (imposed) environment, ∇ ξ a . Our results suggest that it is also unlikely that any similar relationship holds for tropical cyclones. It is shown that conventional methods of averaging over an annular region about tropical cyclone centre to determine the absolute vorticity gradient of the cyclone environment may be very sensitive to the size of the region chosen. For this reason as well as from theoretical considerations our results would indicate that there are certain intrinsic limitations for tropical cyclone track forecasting arising from statistically‐derived relationships between c and ∇ ξ a .