Book Description

ABSTRACT: The process by which tropical cyclones evolve from loosely organized convective clusters into well organized systems is still poorly understood. Due to the data sparse regions in which tropical cyclones form, observational studies of tropical cyclogenesis are often more difficult than similar studies of land-based phenomena. As a result, many studies of tropical cyclogenesis are limited to either a few case studies or are forced to rely on simulations to examine the genesis process. The recent PREDICT and GRIP field experiments have provided a new opportunity to gain insight into these processes using unusually dense observations in both time and space. The present study aims at using this new data to perform a detailed analysis of the three-dimensional evolution of both kinematic (e.g. vorticity and divergence) and thermodynamic (i.e. temperature and moisture) in both developing and non-developing tropical convective systems in the western Atlantic. By examining these structures relative to one another, the nature of the system evolution can be better understood. In order to better capture the true state of the atmosphere in these systems, a new method of calculating vorticity, divergence, and deformation from non-gridded observations using Green's theorem is also presented. Previous approaches using Green's theorem on a non-uniform data distribution have either used triangular regions, which are easily implemented in computer code, or hand-selected polygonal regions, which are more robust. The method presented here combines both convenience and robustness and is shown to be significantly more accurate than triangle-based methods on a random distribution of observations as well as on flight-path-based distributions. Using this new data and analysis method, five tropical convective systems are analyzed- three non-developing and two developing. Although the analysis includes only a limited number of cases, the results suggest that there is little kinematic difference between the developing and non-developing systems. In most cases, the only significant difference between developing and non-developing systems is in the distribution of humidity. In the developing cases the vorticity maxima are encased in high relative humidity values at all levels. In the non-developing cases the vorticity maximum either extends into regions of dry air or mid-level vorticity generation non-existent, likely due to an excessively dry middle troposphere. Additionally, many of the cases, both developing and non-developing, exhibit evidence of vorticity generation associated, at mid-levels, with a mesoscale convective system and, at low-levels, with deep convective activity.