Balancing Accuracy and Efficiency of Atmospheric Models in the Northern Adriatic During Severe Bora Events

In process-oriented studies, accurate representation of severe bora rotor dynamics in the northern Adriatic is known to require the use of model resolutions of the order of 100 m. In regional climate studies, computation time and numerical cost are, however, minimized with resolutions of the order of 10 km. The latter is not accurate enough to drive the coastal dense water formation and the long-term Adriatic-Ionian thermohaline circulation resulting from these events. This work leverages the capacity of kilometer-scale atmospheric models to balance accuracy and efficiency in coupled atmosphere-ocean climate studies in the Adriatic Sea. The sensitivity of severe bora dynamics and air-sea interactions to atmospheric model resolution is thus tested within the Adriatic Sea and Coast (AdriSC) modeling suite as well as with the best available reanalysis. The Weather Research and Forecasting (WRF) model at 15-km, 3-km, and 1.5-km resolution, and ERA5 at 30-km resolution, are compared for an ensemble of 22 severe bora storms spanning between 1991 and 2019. It is found that (1) ERA5 reanalysis and WRF 15-km model highly diverge (up to 43% for the wind speed) from WRF 3-km results while (2) WRF 3-km conditions converge toward the WRF 1.5-km solution for both basic bora dynamics (differences below 6% for the wind speed) and air-sea interactions (differences 5 times smaller than with WRF 15-km results). Consequently, kilometer-scale atmospheric models should be used to reproduce properly the dense water formation during severe bora events and the long-term thermohaline circulation of the Adriatic-Ionian basin.