Sea level perturbations caused by Bora in the northern Adriatic

The Jan. 2014 Bora storm had a measurable impact in the northern Adriatic. At Senigallia, in the wake of the storm, the EsCoSed field experiment (Brocchini et al. in Geology 385:27-40, 2017) recorded 5-cm sea-level fluctuations with a characteristic period of 100 min, exhibiting a distinctive, discrete frequency spectrum. Sea level oscillations of similar height and time periods were also recorded by tidal gauge at Venice. Given the sensitivity of Venice flooding to sea-level perturbations and the localized, basin-transversal jet structure of the Bora winds, the observations are both significant and surprising. We hypothesize that the oscillations were caused by wind setup generated by the Bora jets, and investigate the event using a simplified, linear mathematical model. Model simulations support the wind setup hypothesis and suggest that the oscillations observed were a mixture of edge-waves and two-dimensional seiches with a significant basin-transversal component. The spatial structure of seiches explains the basin-longitudinal reach of Bora storm. A comparison with the analysis of Venice historical records of extreme sea level events, compiled by Ferrarin et al. (Sci Rep 12(1):1-11, 2022), shows that Bora-induced oscillations are of the same order of magnitude as general seiche constituents. Their contribution, however is, much less understood. Further work is needed to evaluate the flooding threat posed by Bora storms.