Relationship betwen tropical cyclone size and diabatic heating profile

The tropical cyclone (TC) size, such as radial extent of 15 and 25 ms-1 surface wind (R-15 and R-25) and eye size, is closely related to the environmental flow around TC. Convective activity modifies the eye structure through the potential vorticity formation due to diabatic heating as found some previous studies. Moreover, a change in vertical profiles of diabatic heating has a large influence on secondary circulation of TC. Thus, the objective of this study is to clarify what relationship exists between TC size and vertical profile of diabatic heating through cloud-resolving simulations.

We use nonhydrostatic model (JMA-NHM) on an f-plane with 2km-mesh. Explicit cloud microphysics is incorporated. The basic state of horizontally uniform temperature and humidity profile is given from averaging reanalysis data of European Centre for Medium Range Weather Forecast (ERA40) over subtropical region of the Western North Pacific in August for 5 years (1998-2002). SST is fixed at 303K. An axisymmetric vortex is embedded in the idealized environment. To examine impacts of diabatic heating profile, we perform three cloud-resolving simulations; one is control experiment, which includes cold-rain processes; second is warm experiment, which includes only warm-rain processes; and third is noevp experiment, which includes cold-rain processes same as the control experiment except evaporative cooling is extracted.

In these experiments, TC eye and eyewall are successfully reproduced. However, the eye size and the R-15 size are quite different between these experiments. The eye size and the R-15 size are larger in warm experiment than in control one. This is considered that enhanced secondary circulation in the warm experiment transports a high absolute angular momentum below the melting layer compared to the control experiment. On the other hand, the eye size is smaller in the noevp experiment than in the control one. The smaller eye size may be caused by a weak transport of absolute angular momentum due to weak inflows below the melting layer. In this presentation, we will further analyze to discuss more details.