Some dynamic characteristics of the east Adriatic coastal area

Abstract

        The results of the dynamic investigations of the coastal area are compared with the known characteristics of the open sea.

        While in the open Adriatic three distinct layers could be distinguished, in the coastal area only two layers are usually present. During the warm period the two layers are separated by the thermocline and the transitory layer has some specific characteristics. In the surface layer the NW, W and N directions prevail. The first direction represents the current entering the Adriatic and going along its eastern coast. Due to configuration of the coastline the same meaning can be given, at least partly, to the N and W directions. But the W direction seems to have another meaning being connected with upwelling and offshore current, all influenced by (NE wind).

        In the bottom layer the directions of the second quadrant (NE, E and SE) prevail. That is the compensatory current with respect to the surface current. The shoreward current (NE and E) brings the water from deeper layers into the coastal area and thus the circulation between the coastal area and open sea is established.

        In the coastal area the dispersion of direction is larger, while the seasonal oscillations in the current field are not so pronounced there as on the open sea. In all the seasons the NW current prevails. In the coastal area, however, the oscilla­tions of several days period are more pronounced, and the energy maximum on these frequencies is greater than the maximum on the frequency of tidal oscillations.

       On the open sea between Ancona and Zadar the tidal oscillations are linear while in the coastal area they perform ellipses. The low-frequency oscillations, ho­wever, show completely opposite characteristics. The absence of the 24 hour oscilla­tion in the region of Vir can be explained by its appearing as the oscillation of lower frequency, due to specific conditions of configuration and friction.

        The current speeds in the surface layer of the coastal area are roughly 50% lower than those on the open sea.   

        The diffusion was experimentally observed on the instantaneous point source in the surface layer in the different dynamic situations. Some problems encountered are discussed.