Relationships Between Tropical Cyclone Structure and Convective Cloud Dynamics

The kinematic and thermodynamic conditions in a tropical cyclone (TC) vary substantially in space, and as a TC structure evolves, in time. This variability yields a spectrum of convective dynamics within a TC. For example, the azimuthal-mean kinematic structure of a TC vortex typically contains substantial variation in both the horizontal and vertical shear of the horizontal wind from the TC's center to its far field. Understanding how the behavior of convective activity varies in a TC is important since the distribution of latent heating, convection-induced circulations, and convective cold pools can impact the structure and intensity of a TC. To contribute toward a better understanding of these complexities, an idealized, convection-resolving WRF simulation of a TC and the Bryan Cloud Model (CM1) are used to study basic aspects of convective morphology in complex kinematic and thermodynamic environments.

The WRF simulation is used to develop initial conditions for idealized convective cloud simulations in CM1. In particular, horizontal and vertical wind shear and thermodynamic profiles are extracted from various radial regions of the azimuthal-mean TC structure during a relatively steady and intense period of the simulated TC. From there, CM1 is used to study the behavior of isolated convection in each of these environments. Sensitivity tests are designed with CM1 to isolate the impacts of horizontal wind shear, the typically veering vertical wind profile, and the thermodynamic background state on convective behavior. We then reexamine the behavior of convection in the WRF simulation to compare how the idealized cloud modeling results apply to a more realistic TC situation produced by WRF. Collectively, these simulations show both the wind shear and background thermodynamic environment have significant impacts on the intensity and longevity of convection. Moreover, horizontal wind shear adds an interesting twist to the dynamics of vertically sheared convection as well. Overall, these idealized experiments add insight into convective processes in the rapid filamentation zone associated with the inner rainband region, the outer rainband region, and potentially the eyewall region as well.