Supervisors info:
Σαράντης Σοφιανός, Επίκουρος Καθηγητής, τμήμα Φυσικής, τομέας Φυσικής Περιβάλλοντος - Μετεωρολογίας, σχολή Θετικών Επιστημών, Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών
Summary:
The aim of this study is the seasonal and interannual variability of the barotropic relative vorticity (RV), enstrophy (ε) and eddy kinetic energy (EKE) in the Mediterranean Sea and its 5 sub-basins (West Mediterranean, Ionian Sea, Levantine Sea, Adriatic Sea and Aegean Sea) for a 20-years-period (1993-2012). RV, ε and EKE are calculated from absolute dynamic topography (ADT) satellite daily data (0.125 degree horizontal resolution, ~14 km), through the estimation of the geostrophic velocity. Mean basin and sub-basin scale circulation is found cyclonic. The study of seasonal cycle, interannual patterns and characterics, as well as 20-year and decadal trends showed that the interannual variability of all parameters (mean RV, ε, EKE) for this period is at least 2 times greater than seasonal variability in all subbasins.
The basin seasonal cycle of mean RV and ε (minimum values in May and maximum values in November) follows that of the latent heat loss. RV seasonal values and range are larger in smaller basins with maximum range and values in Adriatic Sea and minimum in Ionian Sea. Highest mean value and range of the seasonal ε cycle were found for the Aegean Sea and then for the West Mediterranean. The Adriatic Sea shows a solid cyclonic circulation with a strong seasonal cycle (explained variance 32.9% for mean RV and 42.5% for ε), no important trend of cyclonic vorticity throughout the 20 years and the lowest values of anticyclonic vorticity, while the Aegean Sea has a complex combination of strong anticyclonic and cyclonic features impeded in its overall general cyclonic circulation and shows an important interannual variability. Aegean Sea has the largest negative RV trend during this period, anticyclonic vorticity increases throughout the 20 years and becomes greater than cyclonic vorticity in 2012. In the northern Ionian Sea, decadal circulation reversals are found (years 1997 and 2006).
EKE seasonal cycle follows that of the mean RV in the Mediterranean. In contrast to mean RV, EKE variability is more significant in large sub-basins (West Mediterranean, Ionian, Levantine Seas) and in their southern part, where the largest anticyclonic eddies are located. West Mediterranean Sea shows the lowest values of variance explained by the seasonal cycle of ε and EKE. Levantine Sea shows the largest EKE positive trend in the 20 years, which is directly connected to the interannual variability of the Ierapetra anticyclone, the most profound eddy in the whole Mediterranean for this period. The interannual variability of West Mediterranean, follows not only that of EKE as it applies for all large basins but also that of cyclonic and anticyclonic RV.
In a decadal scale, in the large basins (Levantine Ionian, West Mediterranean) there is a positive trend in all parameters (positive and negative RV, ε, EKE) in the first decade but the positive trend applies only for the West Mediterranean in the second decade.
Keywords:
Mediterranean Sea, seasonal and interannual variability, AVISO+ altimetry data, cyclonic and anticyclonic relative vorticity, EKE, enstrophy
