Tropical Cyclones in Decadal High-Resolution Simulations

Earth system models require high resolution to capture the mesoscale dynamics in the eye of a tropical cyclone (TC), which in turn allows more accurate simulation of TC intensity. We approach this so-called TC-resolving regime by using the coupled ICON model with a 10 km grid spacing in the atmosphere and ocean. Our simulations are 30 years long, which allows us to compute climate statistics for TC frequency and intensity. Although relatively high resolutions have been used before, we are among the first to study tropical cyclones with coupled simulations that have global and multi-decadal coverage at 10 km resolution.

We find that ICON is able to reproduce the TC frequency quite well, with about 57 hurricane-scale tropical cyclones per year compared to the observed 48 (as suggested by the "best tracks" dataset). Despite this positive bias in TC frequency, the seasonal cycle of TCs is very close to observations. A TC density map shows good agreement between model and observations, but the model tends to shift cyclone tracks slightly poleward. These differences can be attributed to different large-scale climate conditions, such as vertical wind shear and mid-tropospheric humidity. No category 5 cyclones are simulated, but the model is able to attain higher wind speeds (69 m/s) than any of the coupled climate models in the CMIP6 HighResMIP ensemble. We conclude that ICON, in its high-resolution configuration, is well suited for TC research.