Boundary Layer Structure and Dynamics in Outer Hurricane Rainbands. Part II: Downdraft Modification and Mixed Layer Recovery

Abstract Recent aircraft boundary layer measurements in the vicinity of principal hurricane rainbands have confirmed that convective downdrafts are capable of transporting cool, dry, low equivalent potential temperature (θE) air to the surface, where the mixed layer is eliminated. The incorporation of this air into convection near the core of the storm may weaken the storm, depending upon the scale of the disturbance and the processes governing the recovery of the air while it is flowing toward the eyewall. This paper examines the thermodynamic characteristics of the boundary layer in outer convective hurricane rainbands, providing evidence for downdraft modification mechanisms and determining the extent to which disturbed boundary-layer air may be restored on its trajectory to the storm.