Impacts of atmospheric modes of variability on Mediterranean Sea surface heat exchange

The impacts of variations in the state of the first four modes of atmospheric variability in the North Atlantic/Europe region on air-sea heat exchange in the Mediterranean Sea are considered. Observation-based indices of these modes from the NOAA Climate Prediction Centre are used together with two reanalysis (NCEP/NCAR and ARPERA) surface flux data sets for the period 1958-2006 to determine their relative influence on the mean heat budget of the full Mediterranean basin and the eastern and western subbasins. The modes considered are the North Atlantic Oscillation (NAO), East Atlantic pattern (EA), Scandinavian pattern (SCAN), and East Atlantic/West Russian pattern (EA/WR). Similar results are obtained with both NCEP/NCAR and ARPERA. In each case, winter anomalies dominate the annual mean heat budget and the leading mode, the NAO, has a surprisingly small impact on the full basin winter mean heat budget, <5 Wm^-2. In contrast, the EA mode has a major effect, of order 25 Wm^-2, with similar impacts on both the eastern and western Mediterranean. The SCAN mode has the weakest influence of those considered. The EA/WR mode plays a significant role but, in contrast to the EA mode, it generates a dipole in the heat exchange with an approximately equal and opposite signal of about 15 Wm^-2 on the eastern and western subbasins. A particularly strong impact in the Aegean Sea is observed for the EA/WR mode and this is discussed in the context of episodic deep water formation in this region.