Effect of Horizontal Resolution on the Simulation of TropicalCyclones in the Chinese Academy of Sciences FGOALS-f3 ClimateSystem Model

Abstract. The effects of horizontal resolution on the simulation of tropical cyclones were studied using the Chinese Academy of Sciences FGOALS-f3 climate system model from the High-Resolution Model Intercomparison Project (HighResMIP) for the Coupled Model Intercomparison Project Phase 6 (CMIP6). Both the low-resolution (approximately 100 km resolution) FGOALS-f3 model (FGOALS-f3-L) and the high-resolution (approximately 25 km resolution) FGOALS-f3 (FGOALS-f3-H) model were used to achieve the standard Tier1 experiment required by the HighResMIP. FGOALS-f3-L and FGOALS-f3-H have the same model parameterizations with exactly the same parameters. The only differences between the two models are the horizontal resolution and the time step. The performance of FGOALS-f3-H and FGOALS-f3-L in simulating tropical cyclones was evaluated with the observation firstly. FGOALS-f3-H (25 km resolution) simulated more realistic distributions of the formation, movement and intensity of the climatology of tropical cyclones than FGOALS-f3-L at 100 km resolution. The seasonal cycles of the number of tropical cyclones increased by about 50 % at the higher resolution and better matched the observed values in the peak month, especially in the eastern Pacific, northern Atlantic, southern Indian and southern Pacific oceans. The simulated variabilities of the number of tropical cyclones and the accumulated cyclone energy were both significantly improved from FGOALS-f3-L to FGOALS-f3-H over most of the ocean basins on the interannual timescale. The characteristics of the tropical cyclones (e.g., the average lifetime, the wind–pressure relationship and the horizontal structure) were more realistic in the simulation using the high-resolution model. The possible physical linkage between the performance of the tropical cyclone simulation and the horizontal resolution were revealed by further analyses. The improvement in the Madden–Julian oscillation from FGOALS-f3-H contributed to the realistic simulation of tropical cyclones. The genesis potential index and the vorticity, relative humidity, maximum potential intensity and the wind shear terms were used to diagnose the effects of the resolution. The current insufficiencies and future directions of improvement for the simulation of tropical cyclones and the potential applications of the FGOALS-f3-H model in the sub-seasonal to seasonal prediction of tropical cyclones are discussed.