Lagrangian Coherent Structures in Tropical Cyclone Intensification
Abstract
Recent work has suggested that tropical cyclones intensify via a pathway of rotating deep moist convection in the presence of enhanced fluxes of moisture from the ocean. The rotating deep convective structures possessing enhanced cyclonic vorticity within their cores have 5 been dubbed Vortical Hot Towers (VHTs). In general, the interaction between VHTs and the system-scale vortex, as well as the corresponding evolution of equivalent potential temperature theta(sub e) that modulates the VHT activity, is a complex problem in moist helical turbulence. To better understand the structural aspects of the three-dimensional intensification 10 process, a Lagrangian perspective is explored that focuses on the localized stirring around VHTs and their vortical remnants, as well as the evolution and stirring of theta. Recently developed finite-time Lagrangian methods are limited in the three-dimensional turbulence and shear associated with the VHTs. In this paper, new Lagrangian techniques developed for three-dimensional velocity fields are summarized and we apply 15 these techniques to study VHT and theta phenomenology. Our primary findings are that VHTs are coherent Lagrangian vortices that create a turbulent mixing environment. Associated with the VHTs are hyperbolic structures that modulate the aggregation of VHTs and their vortical remnants. Although the azimuthally-averaged inflow is responsible for the inward advection of boundary layer 20 theta, the LCSs are found to modulate the convection emanating from the boundary layer by stirring theta along organized attracting boundaries. Extensions of boundary layer coherent structures grow above the boundary layer during episodes of convection are responsible for organizing the remnants of the convective vortices. These hyperbolic structures form initially as boundaries between VHTs, but 25 persist above the boundary layer and outlive the VHTs to eventually form the primary eyewall as the vortex attains maturity.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 21, 2011
- Accession Number
- ADA554502
Entities
People
- B. Rutherford
- G. Dangelmayr
- Michael T. Montgomery
Organizations
- Naval Postgraduate School