Exploring the regional coupled capabilities of the ICON modelling framework: The case of medicane Ianos

Mediterranean tropical-like cyclones (“Medicanes”) are fueled by strong sea surface temperature (SST) anomalies and driven by intense atmosphere-ocean interaction processes. These extreme weather events can lead to heavy precipitation, strong winds, severe coastal flooding, and, more generally, catastrophic damage and loss of life over coastal areas. In order to properly forecast such extreme events, accurate modelling of air-sea feedback is crucial, highlighting the need for the development and operative implementation of more complex numerical weather prediction models such as coupled atmosphere-ocean systems. This work presents the first high-resolution (2.5 km) application of ICON-O-LAM, the newly developed regional version of the global ocean model ICON-O, coupled with its atmospheric regional counterpart, ICON-A-LAM. The study focuses on the simulation of Medicane Ianos, which occurred in the Mediterranean Sea in September 2020. The results show that the coupled ICON regional system, when compared with analysis, reanalysis, and satellite observational data, demonstrates clear improvements in representing key storm characteristics if compared to uncoupled simulations, where SST stays constant starting from the initial conditions. The coupled system, particularly when the storm is forecasted even three days before its most intense peak, provides substantial added value by producing more realistic wind intensities, sea level pressure deepening, precipitation intensity, and SST cooling effect. In contrast, the coupled simulations show less added value in improving the accuracy of the storm track, which remains primarily governed by the model initial conditions. The findings presented in this study emphasize the added value of using a high-resolution regional coupled modelling approach for high-impact weather events in semi-enclosed basins like the Mediterranean, where fine-scale ocean-atmosphere feedbacks play a critical role in storm dynamics. • First results from the new high-resolution coupled ICON atmosphere-ocean configuration, with both components operating in Local-Area-Mode, are presented for the IANOS medicane case study. The analysis clearly highlights the added value of the coupled system compared to the uncoupled (atmosphere-only) configuration. • The coupled system better represents the medicane intensity, particularly maximum 10-m wind speed and mean sea-level pressure, thanks to its ability to capture the SST cooling induced by the passage of IANOS. • The coupled configuration shows no clear added value for the storm track, where the dominant factor remains the quality of the initial conditions. • Precipitation during the IANOS event is better reproduced in the coupled system, while the constant SST used in the uncoupled system leads to excessive latent and sensible heat fluxes, resulting in too much evaporation and precipitation. • The analysis of the SST cooling effect shows that the coupled system is well aligned with observations and reanalysis products.