Results of direct current measurements in the Adriatic
Abstract
Results are given on direct current measurements carried out at eight 24hours anchore stations in the middle end south Adriatic (Fig. 1) taken by Ekman current-meter from 1956 to 1962. For each station the maximum and average velocity as well as the direction and velocity of the resultant currents in different seasons are given (Fig. 2, 3 and 4).
Surface currents in the Adriatic generally have a small velocity ranging from 0,3 to 0,8 knots and being greater along the western than along the eastern coast. The velocity of the resultant currents corespond generally to the velocity of gradient currents. Going to the deeper layers the velocity becomes smaller.
The direction of current is different in winter and summer. Superimposed on the general clocwise current system it exist the prevailing tendency of the incoming current to the Adriatic in winter and of the outgoing current in summer (Fig. 5 and 6).
Analogous rhythmical changes in the system of currents found to occur with gradient currents indicate that the currents existing in the Adriatic generally belong to gradient currents. The influence of the wind is only of local importance in the inshore stations (station 6).
The ebb and flow of the tide do not increase the speed of the currents, but their influence is still felt, particularly at some stations where the velocity of the resultant current is small (e. g. in the vicinity of the Island of Vis).
As resulting from the stations lying along the Split-Gargano profile (across the central Adriatic) there is a known transversal current showing constant flow only-at the station No. 12 in the vicinity of the Palagruža Island. This current is evidently caused by the ifluence of the mid-Dalmatian offshore islands and the Palagruža sill in the central Adriatic.
There is a summer current in the intermediary water layer of the open Adriatic (below the depth of 10 m) moving in the opposite direction of the surface current Fig. 7, stations 9 and 12). We have here a current involving the intermediary water laver characterized by a higher salinity rate, i. e. containing water showing the characteristics of southern Adriatic or Mediterranean water. In summer, surface water of lower salinity tends to flow out of the Adriatic, while inflowing water of higher salinity has the tendency to penetrate the intermediary layer of that sea. This dynamic is confirmed by the appearance of the T-S diagram for the region of the middle Adriatic (Fig. 8).
The occurence of year to year considerable fluctuations in the system of currents prevailing in the Adriatic have been confirmed by direct measurements (Fig. 10 and 11). The extent of these measurements, however, should be much greater if the character of the fluctuations and the currents moving in the depth had to be properly known.
