Inner Core Strength of Atlantic Tropical Cyclones

Abstract

The evolution of the wind field beyond the radius of maximum winds is studied for 18 Atlantic tropical cyclones (TCs) with 989 research and reconnaissance flight legs. Inner core strength, defined as the storm relative mean tangential wind from 65 to 140 km from the circulation center for a given flight leg, is shown to be linearly correlated with tropical cyclone intensity. Inner core strengthening coincides with deepening, but as a hurricane decays, the inner core may exhibit a wider range of behavior. During an eyewall replacement cycle inner core strength and intensity become out of phase. Inner core strength tends to be axisymmetric as no quadrant maintains a higher inner core strength than the other quadrants for more than a day. Increases of inner core strength occur throughout the entire 65?140-km radial distance and, thus, are not due to the higher winds found in rainbands alone. The authors speculate that inner core strength, being relatively close to the circulation center, responds efficiently to heat and momentum sources in the eyewall. The behavior differences between inner core strength in these hurricanes and outer core strength in typhoons discussed in earlier works are chiefly a function of distance from the eyewall and appear consistent in light of currently accepted theoretical arguments.