Dynamics of the stratiform sector of a tropical cyclone rainband

Airborne Doppler radar collected observations of the stationary rainband complex of Hurricane Rita (2005) in exceptional detail. Dynamics of the stationary rainband complex play a large role in the evolution of the tropical cyclone's internal structure. The stratiform sector of the stationary rainband complex occurs on the downwind end of the complex. We have examined and characterized the structure and evolution of the stratiform sector and inferred the roles of this feature in the overall storm dynamics.

The stratiform rainband is a mesoscale feature consisting of nearly uniform precipitation and weak vertical velocities from collapsing convective cells. Upward transport and associated latent heating occur within the stratiform cloud layer in the form of rising radial outflow. Below the cloud layer, descending radial inflow was driven by horizontal buoyancy gradients, and thus horizontal vorticity generation, introduced by regions of sublimational and melting cooling. The organization of this transport initially is robust but fades downwind as the convection dissipates. The stratiform-induced secondary circulation resulted in convergence of angular momentum above the boundary layer and broadening of the storm's rotational wind field. At the radial location where inflow suddenly converged, a midlevel tangential jet developed and extended into the downwind end of the rainband complex. This circulation may have also contributed to ventilation of the eyewall as inflow of low-entropy air continues past the rainband in both the boundary layer and midlevels. Given the expanse of the stratiform rainband region, its thermodynamic and kinematic impacts likely help to modify the structure and intensity of the total vortex.