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): The storm-resolving regime should be used to accurately simulate the large-scale flow field and hence the TC intensity (e.g., Gentry and Lackmann, 2010). We approach this regime using the fully coupled ICON model with 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 (e.g., Roberts et al., 2020; van Westen et al., 2023), we are the first to study tropical cyclones with fully coupled, near storm-resolving simulations that have global and decadal coverage.

We find that ICON is able to reproduce the TC frequency quite well, with about 50 hurricane-scale tropical cyclones per year compared to the observed 42 (as suggested by the ”best tracks” dataset). The TC intensity has a slight negative bias in the model, and no category 5 cyclones are simulated. An EOF analysis confirms ENSO as the leading mode of climate variability affecting tropical cyclone frequency. 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, low- to mid-tropospheric humidity, and absolute vorticity. We also want to determine if natural variability can explain the historical negative trend in TC frequency and how the cyclones will change in future climates.

References:

Gentry, M. S., and G. M. Lackmann, 2010: Sensitivity of Simulated Tropical Cyclone Structure and Intensity to Horizontal Resolution. Monthly Weather Review, 138 (3), 688–704, https://doi.org/https://doi.org/10.1175/2009MWR2976.1.

Roberts, M. J., and Coauthors, 2020: Projected Future Changes in Tropical Cyclones Using the CMIP6 HighResMIP Multimodel Ensemble. Geophysical Research Letters, 47 (14), e2020GL088 662, https://doi.org/https://doi.org/10.1029/2020GL088662.

van Westen, R. M., H. A. Dijkstra, and N. Bloemendaal, 2023: Mechanisms of tropical cyclone response under climate change in the community earth system model. Climate Dynamics, 61 (5), 2269–2284, https://doi.org/10.1007/s00382-023-06680-3.