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Several studies show how very high resolution can improve the simulation of wind speed in term of variability and intensity. In this work, we study an intense Bora event using the WRF (Weather Research and Forecasting) model with very high horizontal resolution. The Bora is a katabatic wind mainly associated to two different atmospheric configurations: 1) Cold Air Outbreak events (CAO) triggered by thermal continental anticyclones that transport cold and dry air masses from Siberia to the central Mediterranean sea, and 2) the displacement of a low pressure minimum from the Tyrrhenian Sea towards the Slovenian and Croatian coast. The first case activates a dry and cold air flow from the Dinaric Alps to the Adriatic Sea that extract a large quantity of heat and moisture fluxes from the sea (Adriatic Lake Effect). In the second case, Bora winds are activated by local dynamics and amplified by topography. Many papers have already studied the Bora dynamics, but the present work is one of the first with very-high resolution that adopts a 2-way coupling between atmosphere and waves. In this work, we study a Bora event caused by CAO, using a WRF model with 600 m grid spacing and 60 vertical terrain-following levels. Initial and boundary conditions are taken from ERA-interim dataset. SWAN (Simulating Waves in Nearshore) model is used for simulating wave generation and evolution, and its coupling to WRF is carried out via the COAWST system. In the coupled run, WRF and SWAN exchange data every 600 second. Model results are compared with data recorded every 10 minutes from three stations located inside a Bora jet, namely Vida Buoy (Piran), Paloma Buoy (Trieste) and the "Acqua Alta" tower (close to the Venice coast). Results show that the use of very high resolution increases the model performances both in terms of wind speed (in particular during the peak), and in terms of variability as well; moreover, it reduces bias and RMSE in all stations. The use of coupled atmospheric-wave models, at least for this specific case when winds are larger than 20 m/s, generates larger surface roughness due to waves and, as a consequence, a larger heat and moisture extraction from the sea.

Due to the twofold face of the Adriatic Sea as a shallow coastal sea and as a dense water formation site, the interplay between Bora (a north-easterly wind blowing from the Dinaric alps toward the Italian Adriatic coast, eastern Mediterranean basin) jets and the sea is crucial in conditioning ocean dynamics from the scale of the very coastal processes up to the deep water circulation at the basin scale. In this work we analyse the metocean dynamics associated with Bora jets in the northern Adriatic Sea and in the surrounding coastal regions, with reference to a cold spell event that hit the eastern Europe in January 2017 bringing significant snow falls also in southern Italy and Greece. To this aim, the observational information from in-situ and remote sensing measurements is complemented by a set of numerical model runs carried out within the COAWST system in which different coupling configurations among atmosphere (WRF), ocean (ROMS) and surface waves (SWAN) models are explored, aiming at assessing the potential and the upcoming challenges for model coupling with reference to these events. Preliminary results describe the impact of the explicit description of atmosphere-ocean interactions, and of the waves modulating interface processes, in terms of ocean dynamics (especially concerning evidence from surface quantities), snowfall, and small-scale wind field features. In particular, attention is dedicated to the implications of model coupling with respect to the description of the sharp gradients characterising the coastal zones, where shortcomings in satellite products and numerical models most usually arise. This study was funded by the UE H2020 programme under grant agreement No. 730030 (CEASELESS Project, Coordinator Agustin Sanchez-Arcilla).