Hrvatsko meteorološko društvo

Unusual thermohaline situation, which lasted from 1987 to 1998, was determined by using long-term time series of mean monthly temperature and salinity at three stations along Palagruža sill. Climatic condition was characterized by a temperature of intermediate layer, which were more than two standard deviations lower than the climatological average. The cause of the anomaly was found in the hemispheric atmospheric processes that modify regional atmospheric parameters by teleconnection, and indirectly influence the termohaline properties of the sea. Thermohaline conditions of the Adriatic Sea can be found in at least two different climatic conditions. In the first period (1963-1986), the hemispheric atmospheric NAO and AO indexes oscillated from their positive to negative phase. Over the Adriatic, air temperature was lower and evaporation and precipitation higher than the climatological average. In the first climatic period, the sea-atmospheric boundary layer during the winter was characterized by frequent outbrakes of cold air, followed by bora, which enabled the creation of NAdDW in the northern Adriatic. Exchange of water through the Otranto Strait, between the Adriatic and the Ionian Sea was significant. Second climatic condition lasted from 1987 to 1998. During this period, hemispheric atmospheric NAO and AO indexes were in their positive phase, which increased the mean Adriatic winter air pressure. Winter air temperature was higher than the average, and outbrakes of cold air followed by bora less frequent. Evaporation in the northern Adriatic Sea was reduced, causing reduced creation of NAdDW. Due to the frequent breaches of polar air, deep water intensively began to create in the Aegean Sea instead of the Adriatic Sea. Above mentioned hemispheric and regional atmospheric processes were reflected in the thermohaline properties and circulation of the Adriatic Sea. In the second climate period, exchange of water between the Adriatic Sea and the Ionian Sea was reduced.