Numerical study of the north Adriatic circulation during two successive bora episodes

Abstract

       The north Adriatic circulation during two successive bora episodes was studied using single point current measurements and results of the Princeton Ocean Model (POM). Surface currents recorded at the gas field Ivana positioned in the central part of the northern Adriatic were directed downwind during the bora episode of 8-11 February 1984, whereas during the next bora period of 12-16 February 1984 they were directed upwind. The observed current reversal was reproduced in the numerical experiment controlled by air-sea fluxes and river inflows. Atmospheric forcing for the POM model was estimated from high resolution Mesoscale Model 5 (MM5) surface fields, while river discharges were introduced in the simulations as source terms of zero salinity in the continuity equation. The baseline experiment with realistic forcings, atmospheric and riverine, related the current reversal to displacements of the bora induced gyres. Sensitivity studies revealed a dominant role of the wind stress curl for the vorticity in the current field and showed the relevance of the changing wind divergence for the cross-shore circulation variability and accompanied current reversal. Additional numerical experiments emphasized even more the role of the spatial wind variability for the recorded flow and also stressed the importance of the model domain size for the numerical results.