Links between tropical cyclone structure and intensity change derived using aircraft data from 2000-2012

The physical processes governing tropical cyclone (TC) intensity changes are not fully understood. Increasing our knowledge of mesoscale processes remains vital to improving TC intensity forecasting. Recent studies have proposed that the radial structure and convective activity of intensifying TCs differs from those that are steady-state or weakening. The efficiency of intensification has been attributed to the radial location of convective bursts with respect to the radius of maximum tangential wind (RMW), where convective bursts were preferentially located inside the RMW for intensifying TCs and outside the RMW for steady-state TCs. Understanding the link between the physical processes responsible for intensity change and radial structure differences could lead to more accurate TC intensity forecasting. In this study we consider radial structure differences due to both TC intensity and intensity change through a comprehensive examination of in situ measurements in Atlantic hurricanes obtained from the Extended Flight Level Dataset (FLIGHT+). In situ data at the 700 hPa flight level from 156 flights into TCs from 2000-2012 have been collected from NOAA WP-3D and USAF WC-130 aircraft. Flights were organized by both the TC's intensity and 12 hour intensity change determined from the National Hurricane Center's Best Track (BT) dataset. A matrix of composite structures was then calculated for hurricanes (Categories 1 and 2 on the Saffir-Simpson scale) and major hurricanes (Categories 3 and above) that were intensifying [IN, intensity increase ≥ 10 kt (12 h)-1], steady-state [SS, intensity change between ± 5 kt (12 h)-1], and weakening [WK, intensity decrease ≤ -10 kt (12 h)-1]. Radial composites of axisymmetric tangential wind, vorticity, inertial stability, and absolute angular momentum were created using a non-dimensional analysis that facilitates inter-comparisons of TC radial structure. Radial structure differences between composites were larger in the inner-core region slightly inside the RMW for hurricanes, but were larger outside the RMW for major hurricanes. Hurricane IN composites have the highest vorticity and inertial stability slightly inside the RMW, followed by SS and then WK composites, suggesting a link to the radial location of convective bursts. Absolute angular momentum was smaller outside the RMW for hurricane and major hurricane IN composites, suggesting a link with variations in the TC secondary circulation.