Tropical Cyclones in High-Resolution Global Climate Simulations with the IPSL Model

The availability of a new icosahedral dynamical core (DYNAMICO) for the IPSL model was the opportunity to participate in the HighResMIP protocol. We present the results of four historical 1950-2015 atmosphere-only (forced SST) simulations at horizontal resolutions equal to 200, 100, 50, and 25 km. We compare them with two simulations that use the same configuration but were performed with the previous longitude-latitude dynamical core at 250 and 75km horizontal resolutions.

We use these simulations to perform the first assessment of Tropical Cyclones (TC) in the IPSL model. This evaluation is done across four resolutions, gathering methodologies from recent literature (Roberts et al., 2020 a&b; Moon et al., 2020; Chavas et al., 2017; Camargo et al., 2020; Bourdin et al., 2022).
We first show that the results obtained with DYNAMICO compare favorably with the previous dynamical core of the IPSL model.
Then, we analyze how increasing horizontal resolution from 200km to 50km improves the TC climatology. Our results align with the current expectation that frequency and geographical distribution get closer to the observation but that the intensity is still significantly under-resolved.
In the highest-resolution simulation TC activity in the North Atlantic basin is well represented in terms of geographical distribution and inter-annual variability. However, regional biases remain, especially in the Western North Pacific, where there is a significant deficit in TC number and a shift of activity towards the east of the basin. These regional biases are robust with resolution but are not associated with any obvious climatological bias in the simulations.
Finally, we study composites, TC size, and life cycles to document the physics of the model's TCs. They show that the model simulates realistic TC structures with primary and secondary circulations, an eyewall, and a warm core. TC size diminishes with resolution and less so with intensity.

We conclude that the IPSL model is able to simulate a realistic climatology of Tropical Cyclones at 25 km horizontal resolution, with maximum intensities limited by the current maximum resolution.