Interactions between Roll Vortices and Large-scale Flow in the Hurricane Boundary Layer

Observations indicate that roll vortices (rolls) are prevalent in the hurricane boundary layer (HBL). Rolls may play an important role in the vertical transports in the HBL and therefore influence the large-scale hurricane structure. Recent studies suggest that rolls can be generated by the inflection point instability of the HBL flow. However, it still remains unclear how these rolls interact with the large-scale hurricane flow after they reach finite amplitudes. We have developed a two-dimensional high-resolution (30m) Single-grid Roll-resolving Model (SRM) that can be embedded at multiple locations in a hurricane model. SRM resolves rolls at a single grid in the hurricane model based on the local mean flow profiles, and provides the roll-induced fluxes to the hurricane model. We have investigated the evolution of rolls and their effects on the mean flow in an idealized HBL model. Some interesting behaviors of rolls and mean flow were found after rolls reach finite amplitude. We found rolls periodically trigger internal wave generation. And this wave generation seems to be closely related to the inertial oscillation of the mean wind. Rolls greatly enhance the vertical momentum fluxes in the HBL and modify the mean HBL wind distribution. Particularly, roll-induced momentum fluxes lead to a reduction of inflow speed and an increase of the inflow layer height, suggesting rolls may have important implications on the evolution of the hurricane.