Secondary eyewall formation in WRF simulations of Hurricanes Rita and Katrina (2005)

An analysis is presented of two high-resolution hurricane simulations of Katrina and Rita (2005) that exhibited secondary eyewall formation (SEF). The results support the notion of vortex Rossby waves (VRWs) having an important role in SEF and suggest that VRW activity is a defining aspect of the moat. SEF occurs at a radius of similar to 65 (80) km in Katrina (Rita), close to the hypothesized stagnation radius of VRWs. VRW activity appears to be the result of eye-eyewall mixing events, themselves a product of the release of barotropic instability. The convection in the radial region that becomes the moat is mainly in the form of VRWs propagating radially outward from the primary eyewall until the negative radial gradient of potential vorticity is no longer conducive for their propagation. These convectively coupled waves, originating and being expelled from the eyewall, are rotation dominated and have the coherency necessary to survive their passage through the strain-dominated region outside the eyewall. Citation: Abarca, S. F., and K. L. Corbosiero (2011), Secondary eyewall formation in WRF simulations of Hurricanes Rita and Katrina (2005), Geophys. Res. Lett., 38, L07802, doi:10.1029/2011GL047015.