Stronger Vertical Shear Leads to Earlier Secondary Eyewall Formation in Idealized Numerical Simulations

Idealized numerical experiments show that stronger shear is more favorable for tropical cyclone secondary eyewall formation (SEF) than weaker shear amid a moist-tropical environment when the shear magnitude is smaller than 15 m s(-1). In particular, the larger the shear, the earlier the SEF occurs. A stationary banding complex (SBC) prevails before SEF in the large shear experiments, suggesting that SBCs are helpful in the SEF. Furthermore, a well-organized stratiform sector is associated with the SBC. With increasing shear, the shear-forced outflow also increases in the upper layers, transporting more moisture and icy particles outward from the inner core and favoring the development of the stratiform sector. The diabatic cooling of the stratiform sector strengthens the underlying descending radial inflow, forcing updrafts immediately outside the inner core. The subsequent axisymmetrization of the updrafts leads to SEF.

Automated summary

Idealized numerical experiments demonstrate that stronger shear is more favorable for the formation of tropical cyclone secondary eyewall (SEF) in a moist-tropical environment. The larger the shear, the earlier the SEF occurs. A stationary banding complex (SBC) exists before SEF in experiments with larger shear, indicating that SBCs are beneficial for SEF. Additionally, a well-organized stratiform sector is associated with the SBC. With increasing shear, the shear-forced outflow increases in the upper layers, leading to the transportation of more moisture and icy particles from the inner core and promoting the development of the stratiform sector. The diabatic cooling of the stratiform sector strengthens the underlying descending radial inflow, resulting in updrafts immediately outside the inner core. The subsequent axisymmetrization of the updrafts leads to SEF.