The Dynamic Response of the Hurricane Wind Field to Spiral Rainband Heating

The response of the hurricane wind field to spiral rainband heating is examined by using a three-dimensional, nonhydrostatic, linear model of the vortex-anelastic equations. Diabatic heat sources, which are designed in accordance with previous observations of spiral rainbands, are made to rotate with the flow around the hurricane-like wind field of a balanced, axisymmetric vortex. Common kinematic features are recovered, such as the overturning secondary circulation, descending midlevel radial inflow, and cyclonically accelerated tangential flow on the radially outward side of spiral rainbands. Comparison of the responses to the purely convective and stratiform rainbands indicates that the overturning secondary circulation is mostly due to the convective part of the rainband and is stronger in the upwind region, while midlevel radial inflow descending to the surface is due to the stratiform characteristics of the rainband and is stronger in the downwind region. The secondary horizontal wind maximum is exhibited in both convective and stratiform parts of the rainband, but it tends to be stronger in the downwind region. The results indicate that the primary effects of rainbands on the hurricane wind field are caused by the direct response to diabatic heating in convection embedded in them and that the structure of the diabatic heating is primarily responsible for their unique kinematic structures. Sensitivity tests confirm the robustness of the results. In addition, the response of the hurricane wind field to the rainband heating is, in the linear limit, the sum of the asymmetric potential vorticity and symmetric transverse circulations.