How can severe rapid intensification of super-intense typhoons be revealed by the evolution of lower-stratospheric potential vorticity?

Rapid intensification (RI) of super-intense typhoons is investigated by ocean-coupled HWRF simulations. The simulation of Supertyphoon Yutu (2018) indicates a faster pronounced increase in lower-stratospheric potential vorticity (LSPV) than in tropospheric potential vorticity (TPV) within the inner typhoon. During the early RI stage, the intensifying LSPV in the ambient PV reservoir is transported inward to the eye and downward to the upper eye through mean and asymmetric eddy advection in the PV budget to provide feedbacks with the TPV at upper levels. The solution of the extended Sawyer-Eliassen (SE) equation, with a relief of balance dynamics, indicates that the RI becomes more severe, due to the enhanced spinup near the upper-level eye induced by diabatic heating and the eyewall in 12–18-km height by asymmetric eddy forcing, in association with a stronger spinup in the eyewall below 12-km height induced by diabatic heating. A significant spinup in the mid-lower eye region, however, can be produced by eddy forcing, in association with the primary eyewall spinup in response to the quickly increasing TPV as the LSPV also becomes stronger. Averaged LSPV and TPV amounts within the inner vortex exhibit high correlations with the actual vortex intensity. Stronger LSPV highly correlated with the vortex intensity also exists for other supertyphoons, Megi (2010), Haiyan (2013), and Goni (2020), all undergoing severe RI, but not for Mangkhut (2018) developing only marginal RI in short of the LSPV. TPV alone does not clearly explore the severity of RI, without referring to the growth rate of LSPV.