Tropical cyclone initialization and dynamic adjustment: Sensitivity studies

In this study, we explore the adjustment phase of synthetic tropical cyclone data in a three-dimensional full physics numerical model using a 6-day simulation as a nature run. Using a recently developed, highly configurable vortex initialization algorithm, the sensitivity of the early evolution of tropical cyclone like vortices to the presence of an initial secondary circulation, boundary layer eddy diffusivity coefficients, and enhanced moisture anomalies are investigated. In the initialization algorithm, the inserted vortex is in gradient wind and hydrostatic balance. However, the initial vortex is not balanced with the environment.

It is hypothesized that the introduction of an initial secondary circulation will mimic the influence of a frictionally convergent boundary layer on development, thereby yielding realistic early evolutions despite the inclusion of a synthetic vortex. Preliminary results suggests that the initial secondary circulation does yield more rapid development over the first few hours as defined by common intensity metrics. However, spin-down is nonetheless observed, particularly with weak initial circulations. With strong initial circulations, it is possible that more rapid early development observed may persist until frictional convergence from the boundary layer physics becomes dominant.

We further explore the addition of a moisture anomaly to the core region. The moisture anomaly acts to accelerate development but may result in a weaker equilibrium intensity. Explanations for this behavior are ongoing. Finally, we will consider the role of the eddy diffusivity coefficient in the initial boundary layer structure. Varying this coefficient offers the flexibility to adjust the surface tangential wind maximum and the initial secondary circulation strength.