A closer look at tropical cyclones in vertical shear flow: Diabatic heating and vortex resliency

It is well-established that hurricane-strength vortices possess the ability to remain vertically aligned in external vertical shear flow through an intrinsically dry dynamical mechanism. This vortex resiliency in shear was originally demonstrated for uniform static stability conditions characteristic of the average tropical environment. A reduction in the static stability (e.g., through saturated ascent) alters the dry resiliency mechanism. We will explore here in the context of a wave-mean framework how the vertically-sheared vortex responds as the static stability is reduced to the neutral limit. Motivated by observations of Hurricane Guillermo (1997), the impact of spatially variable static stability on tropical cyclone resiliency is also examined.

Whether the dry dynamical model of tropical cyclone resiliency in vertical shear flow continues to be a useful paradigm when explicit moist processes are active remains an open question. In our initial approach to answering this question, diabatic heating is first included as a symmetric forcing in a linearized primitive equation model and then in the Weather Research and Forecast (WRF) model. Preliminary results from this investigation will be presented.