Sensitivity of Tropical Cyclone Development to the Vortex Size Under Vertical Wind Shear

The sensitivity of tropical cyclone (TC) intensification to its inner size in a sheared environment is investigated in this study. Previous research indicated that TCs with smaller sizes spin up more quickly in a quiescent environment. In contrast, our idealized numerical simulations show that TCs with larger inner-core sizes experience faster growth within a certain size range under the vertical wind shear (VWS) because stronger upper-level outflows are established quickly for larger TCs. The presence of strong outflow diminishes the impact of VWS, causing the TC re-alignment. In more detail, the stronger outflow locally reduces the shear, allowing the convective asymmetry to propagate to the upshear side and migrate inward toward the TC center more rapidly. The upshear convection leads to a stronger outflow and thus a greater blocking effect on the upper-level wind, effectively reducing the VWS and thus allowing subsequent faster TC growth. Our analysis reveals that the TC re-alignment at an earlier stage allows for significant differences in surface heat flux (surface latent heat flux [SLHF]) distribution based on size. Larger TCs exhibit larger areas of high SLHF, which create favorable thermodynamic conditions for TC developments. Conversely, smaller vortices have limited SLHF underneath, resulting in a prolonged intensification process. Furthermore, the boundary layer recovery mechanism effectively counteracts the low-level ventilation pathway imposed by the shear. This mechanism supports the downstream deep convection development on the upshear side. This study presents a new perspective, highlighting that the impact of shear on TCs is contingent upon their sizes upon entering a sheared environment. The paper shows that a tropical cyclone (TC) with a larger inner-core size experiences rapid intensification in the presence of vertical wind shear (VWS). Our findings indicate that when the TC has a larger inner-core size, the enhanced inner-core convection can increase the upper-level outflow, which helps to resist the upper-level environmental wind and reduce the VWS. This leads to the TC re-alignment and allows for faster development. The large-size TC possesses a larger area of high surface heat flux that provides abundant energy for TC development. This finding emphasizes a new perspective, highlighting that the impact of shear on TC development is contingent upon the size of the TC itself. In the presence of vertical wind shear (VWS), tropical cyclone (TC) with a larger size is apt to experience a high intensification rateTC with a larger size quickly develops stronger upper-level outflow, which helps decrease VWS. This leads to TC re-alignment and faster developmentThe TC with a larger sizes possesses a larger area of high surface heat flux, favoring the thermodynamic forcing for TC rapid development