Modulation of the Wind Field Structure of Initial Vortex on the Relationship between Tropical Cyclone Size and Intensity

This study investigates the modulation of initial wind field structure on the relationship between the size and intensity of a simulated vortex. A series of idealized experiments are conducted by varying the radius of maximum wind (RMW) and shape parameter b of the initial vortices. The size-intensity relationship is quantified by the linear regression coefficient of the azimuthally-averaged gale-force wind radius against the maximum wind during the development stage, reflecting the degree of size expansion at the same intensity increment. The regression coefficient increases with increased RMW and decreased b, with the RMW being the primary constraint. The effect of lowering b on the elevation of the regression coefficient gradually stands out when the initial RMW is large. Enlarging the RMW leads to a secondary circulation with a horizontally elongated structure, which retards the intensification while promoting size expansion, thus substantially enhancing size expansion as the vortex intensifies. Broadening the wind field outside the RMW by reducing b results in abounding convection in the outer region, which promotes size expansion. Based on the axisymmetric tangential wind tendency and Sawyer-Eliassen equations, when the RMW is large, the active convection in the outer region can weaken the radial inflow induced by the eyewall heating in the inner region, thus retarding the intensification by reducing the radial imports of vorticity near the RMW.