On the Asymmetric Structure of the Tropical Cyclone Outflow Layer

Abstract

ATS-III satellite data and conventional aerological data are used to construct detailed wind analyses of the outflow layer for four hurricanes and one tropical storm. Harmonic analysis of these data, and of the data for a mean Atlantic hurricane and a mean Pacific typhoon, shows that wave numbers 1 and 2 around the circumference of the storm account for most of the variance of momentum and kinetic energy. Subtraction of the symmetric part of the vortex circulation from the total flow to yield the ?asymmetric wind? reveals two eddies located in preferred quadrants of the storm. An anticyclonic eddy is found to the right and a cyclonic eddy to the left of the storm motion. These eddies transport absolute vorticity inward, opposing the outward transport by the mean circulation. They also transport a significant amount of negative relative angular momentum outward. The presence of inertial (or dynamic) instability is investigated. Although substantial areas of negative absolute vorticity and anomalous anticyclonic winds exist in all cases, these areas are correlated so well that the regions of dynamic instability are small.