A balanced model of a hurricane vortex coupled to a boundary layer

The boundary layer plays a key role in several aspects of hurricane dynamics. Here we focus on its contribution to the balanced circulation. Previous studies, whilst including centrifugal terms, have not included an explicit balance in the boundary layer. Here, we improve the balanced theory to include an Ekman balance, the so-called frictional axisymmetric vortex (FAV). This approach is analogous to semigeostrophic theory that includes realistic boundary-layer diffusion: semigeotriptic (SGT) theory. We formulate the FAV for an axisymmetric system in cylindrical polar coordinates. We then derive a Sawyer–Eliassen equation for the vertical circulation. Example solutions for idealised hurricane-scale and synoptic-scale vortices are compared.