Impacts of Off-Center Coefficient，Model Horizontal Resolution and Time Step on Modelling the Rapid Intensification of Super Typhoon ‘Chanthu' in 2021

Rapid intensification of TC is the most challenging issue for NWP system. A cloud resolving model is the first step for the prediction and the simulation. A 3-5km regional Typhoon Model has been under development in CMA Earth System modelling and prediction Centre (CEMC) since 2022, which is planned to be an upgrading of the operational CMA-TYM (named GRAPES_TYM before Sep. 2021) with 9km resolution. The stable and computer resource are the first two problems need to be solved in order to put it into operation since CMA-TYM has a larger integration domain covering 40-180°E and -15-60°N.

CMA-TYM adopts a two-time level Semi-implicit Semi-Lagrangian integration scheme. This integration scheme can have a larger time step for a limited computation resource but has lower accuracy for higher gradient weather systems.

In this paper, the sensitive experiments on the off-center coefficient in the Semi-implicit Semi-Lagrange scheme, the model resolution and the time step are carried out to illustrate the impacts to the simulation of the rapid intensification of Super Typhoon ‘CHANTHU’ in 2021, which experienced a rapid intensification during the early stage of its life history- the maximum wind speed increased 40m/s and the central pressure decreased 75hPa within 24h.