Dependence of tropical cyclone inner-core size and intensity on the initial vortex size

The multiply nested, fully compressible, nonhydrostatic tropical cyclone model – TCM4 is used to examine and understand the sensitivity of the simulated tropical cyclone (TC) inner-core size and intensity to its initial vortex size. The results show that although the simulated TC intensity at the mature stage is weakly dependent on the initial vortex size for the general settings, the simulated TC inner-core size is largely determined by the initial vortex size. The initial vortex size on one hand is critical to the energy input from the ocean and on the other hand is important to the effectiveness of the inward angular momentum transport by the transverse circulation driven by eyewall convection. Strong outer winds in storms with a large initial size lead to large entropy fluxes and thus high convective available potential energy (CAPE) to a large radial extent, favoring the development of active spiral rainbands outside the eyewall. Latent heat released in spiral rainbands plays a key role in increasing tangential winds outside the eyewall, contributing to the increase in the inner-core size of the simulated storm. On the contrary, storms with a small initial vortex size have weaker outer winds and are accompanied with weaker spiral rainbands and thus a much slower increase in the inner-core size. The relative importance of the initial vortex size and the environmental relative humidity (RH) to the TC inner-core size is also evaluated. It is found that the inner-core size of the simulated storms at the mature stage is dependent more on the initial vortex size than on the initial RH of the environment.