Mediterranean Oscillation and its relationship to salinity fluctuation in the Adriatic Sea

Oceanographic conditions in the Adriatic Sea strongly depend on inflows of highly saline and warmer LIW from the eastern Mediterranean as well as on the formation of cold, dense water in the North Adriatic. Both phenomena have different intensity from one year to another. Pressure field distribution, over the area larger than the Adriatic regulates both mechanisms. Stronger inflows were observed when high pressure over the North Atlantic and lower pressure over the East Mediterranean occurred, i.e. when horizontal pressure differences between these areas were higher. As the intensity of inflow varies from one year to another, a water mass distribution follows year-to-year fluctuations. To find out what meteorological processes determined main Adriatic inflows, intermediate Middle Adriatic salinity fluctuations were discussed in relation to the NAO, and pressure fields over the Europe. From the long-term pressure field data, main variability patterns were extracted, using the Principal Component Analysis. The analysis reveals the presence of the strong inter-annual correspondence between the time evolutions of the modes responsible for the pressure field over the Mediterranean and Atlantic, and the Adriatic salinity. Further analysis enabled locating the areas whose pressure is directly related to the inflow phenomena, which generally causes higher salinity in the Adriatic. These analyses led to the definition of the Mediterranean Oscillation index (MOI).