Effect of Boundary Layer Roll Vortices on the Structure and Intensity of the Hurricane

Recent observational and modeling studies suggest that quasi-two-dimensional horizontal vortices, commonly known as rolls vortices (rolls), frequently exist in the hurricane boundary layer (HBL). However, little has been known about their impact on the structure and intensity of the hurricane. In this study, we numerically investigate the effect of rolls on the development of an axisymmetric hurricane. To represent the vertical fluxes induced by rolls, we embed a small-scale 2-D roll-resolving model at multiple horizontal grid points in the 3-D hurricane model (COAMPS-TC) domain. It is found that the rolls first induce changes in the boundary layer wind distribution, which then lead to an increase in the hurricane intensity. Sensitivity experiments suggest that the roll-induced tangential momentum flux is primarily responsible for the enhanced hurricane intensity, and the rolls generated at different radii (within the range we consider) all positively contribute the hurricane intensity. The mechanism through which the rolls affect the hurricane development is also revealed. We find that the rolls trigger a cascade of dynamical responses within the HBL, increasing the mass convergence and inducing a more active deep eyewall convection, which leads to enhanced hurricane intensity.