Widening of Tropical Cyclone Scale Projected By Multi-Decadal Experiments with a 14km-Mesh Global Nonhydrostatic Model

We investigated future changes in tropical cyclone (TC) structure simulated by 30-year simulations under present-day and warmer conditions using a 14km-mesh nonhydrostatic icosahedral atmospheric model (NICAM) with explicitly calculated convection. The responses of vertical and horizontal structures to global warming are investigated for TCs with the same intensity categories. In this study, TCs are categorized with respect to the minimum central sea-level pressure (SLP) during their lifecycles (i.e., lifetime maximum intensity) following Roberts et al. (2015). For TCs whose minimum central SLP reaches less than 980 hPa, tangential winds were projected to increase in the outside region of the eyewall when compared between TCs in the same intensity categories under the two climate conditions. Increases in the tangential winds are related to the elevation of the tropopause caused by global warming. The tropopause rise induces an upward extension of the eyewall, resulting in an increase in condensation heating in the upper layers of the inclined eyewall. Thus, SLP is reduced underneath the warmed eyewall regions through hydrostatic adjustment. The altered distribution of SLP enhances tangential winds in the outward region of the eyewall cloud. Hence, this study shows that the horizontal scale of TCs, such as defined by the radius of 12 m s^-1 surface wind, is projected to increase if compared for the same intensity categories.