The role of Lagrangian coherent structures in tropical cyclone formation

We investigate the role of Lagrangian coherent structures in tropical cyclone formation, using new sophisticated 3D mathematical techniques. The techniques involve a decomposition of the velocity fields, and reveal a series of coherent structures. The structures are persistant across a wide range of time scales, and through shear, giving a natural application to tropical cyclones. The techniques that we have developed show not only inner core structures, but also the environmental structures, and the interaction between these structures is shown. The benefit of our methods is that Vortical hot towers (VHT) and environmental features can be analyzed in the same computation, which gives significant insight into the role of environmental factors in VHT interaction, and therefore intensification. A recent study by Haller and Sapsis (2009) also showed Lagrangian coherent structures in a tropical cyclone. In our study, we find many of the same structures, but our techniques have several key advantages, including our handling of shear, finding and further categorizing additional structures, and we require less model data due to the fast convergence of our algorithms. The structures that we show are quite different than structures traditionally seen in tropical cyclones, but are important for their role in intensification because they dictate Lagrangian transport.