Highly idealized three-dimensional nonlinear simulations and some aspects of the problem of the secondary eyewall formation

Some aspects of the problem of the secondary eyewall formation (SEF) are investigated with the aid of a highly idealized model. A series of experiments are conducted, starting with a strong annular vortex embedded in a quiescent background flow and forced by the sustained heat associated with a spiral rainband (control). Followed, two experiments are configured to assess the impact of vertical wind shear (VWS) in the SEF process. Finally, the importance of the boundary layer force imbalance is investigated in a simulation in which surface and boundary layer physics are included.

From the control experiment, it is found that in the absence of background environmental flow, the sustained latent heat associated with a spiral rainband can form a secondary eyewall even in the absence of a frictional boundary layer. The presence of VWS act negatively onto the SEF process, by disrupting the organization of the potential vorticity included by the rainband. Finally, when the boundary layer physics are included similarities with previous studies are seen, but there is no SEF. These results question the ``key'' importance of the unbalance boundary layer dynamical processes and further suggests that the boundary layer most likely contributes rather than initiating a secondary eyewall.