Currents in the Kaštela Bay: empirical analysis and results of a numerical model

Abstract

         Basic statistical analysis of all available current data from the Kaštela Bay for a period between 1953 and 1990 shows the importance of the sirocco wind in generating the circulation of the Bay. Strong episodes of sirocco reverse the estuarine circulation in the Bay inlet. During sirocco episodes current polarisation in the east-west direction is observed, with a downwind current in the surface layer and the compensatory current in the deeper layers. In the Bay interior sirocco-induced surface currents turn to the right of the wind direction under the influence of the CORIOLIS force. During strong wind periods the mean current speeds in the Bay interior are almost half of those in the Bay inlet, pointing to the importance of the wind-induced transports from the adjacent Brač Channel.

            Numerically obtained basin-wide cyclonic circulation during bora wind is in agreement with the conclusions of the salinity measurement analysis. Numerical results show the formation of several cyclonic and anticyclonic gyres during sirocco, so at least in some parts of the basin theoretical results and empirical findings stemming from the salinity distribution are in agreement. Comparison of direct current measurements with the results of the numerical model shows good agreement during sirocco episodes, whereas the agreement is lower during bora. Proper prediction of the wind-induced currents demands detailed knowledge of the wind stress magnitude and direction above the Kaštela Bay and of the density distribution in the sea.