Hydrological Characteristics and Dynamics of the Northern Adriatic during Late Summer and Autumn 1997

Abstract

Horizontal and vertical distributions of the hydrological data monitored during the autumn campaign of the PRISMA 2 project in the Northern Adriatic in 1997 show the presence of various mesoscale cyclonic and anticyclonic structures, as well as a strong coastal front separating water of fluvial origin from that of the open sea. The surface layer, in the southern part of the studied area, presents higher density and salinity than in the northern part due to the cyclonic nature of the basin-scale Adriatic general circulation. On the contrary, the presence of a low density core in the bottom layer probably indicates an anticyclonic circulation. The application of a statistical method, cluster analysis, to temperature and salinity data have permitted the individuation of three groups with distinct characteristics, corresponding to three different water masses. Their spatial extension is in concordance with the oceanographic conditions already observed in the Northern Adriatic. The dynamic characteristics were obtained from ship-mounted ADCP current measurements to which the “detiding” method of Candela has been applied. The steady part, in agreement with the general circulation of the Adriatic Sea, indicates currents flowing southwards along the Italian coast; additionally there are indications of a sub-basin cyclonic circulation to the north of the Po river mouth. On the contrary, the low frequency residual current field shows a variable spatial structure, with currents alternating northward and southward, that broadly agrees with the horizontal and vertical distribution of the thermohaline parameters. Finally, it is observed that where water of fluvial origin is present, the residual current field indicates southward flow. The M2 tidal ellipses, as expected, are polarised in the centre of the basin along the NW-SE direction, while along the boundaries, they follow the coastline orientation.