Formation and Replacement Mechanism of the Concentric Eyewall of Super Typhoon Muifa (1109)

Based on high-fidelity numerical simulation by using the Weather Research and Forecast (WRF) model, we analyzed the formation and replacement mechanism of the concentric eyewall of Super Typhoon Muifa (1109) from the aspects of the potential vorticity (PV), dynamic/ thermodynamic structure change, sea surface flux, and water vapor content. Observational data and sensitivity tests were also adopted to verify the results. We found that: (1) The abnormal increase of the PV in the rain zone is mainly due to the condensation latent heat. Sufficient water vapor conditions are beneficial to the formation of the outer eyewall structure, and when the environmental water vapor content is larger, the intensity of the outer eyewall becomes greater. (2) After the formation of the typhoon's outer eyewall, in the area where the outer eyewall is located, the increase of inertial stability contributes to the decrease of the intensity of the inner eyewall. When the intensity of the outer eyewall is larger, the divergence and subsidence motion in the upper layer of the outer eyewall has a greater weakening effect on the intensity of the inner eyewall. (3) The increase of potential temperature of the outer eyewall is mainly due to the condensation latent heat release and the warming of dry air subsidence motion in the moat area. (4) The increase of sea surface heat flux can prolong the concentric eyewall replacement process.