Impact of the atmospheric climate modes on Mediterranean sea level variability

• The NAO is the primary contributor on winter Mediterranean sea level variability.
• The EA/WR is the 2nd mode in importance on the atmospherically-induced sea level.
• The EA pattern dominates the rate of change of winter thermosteric sea level.

The relationships of Mediterranean sea level, its atmospherically driven and thermosteric components with the large scale atmospheric modes over the North Atlantic and Europe are explored and quantified. The modes considered are the North Atlantic Oscillation (NAO), the East Atlantic pattern (EA), the Scandinavian pattern (SCAN) and the East Atlantic/Western Russian (EA/WR). The influence of each mode changes between winter and summer. During winter the NAO is the major mode impacting winter Mediterranean sea level (accounting for 83% of the variance) with SCAN being the second (56%) mode in importance. Both NAO and SCAN effects are partly due to direct atmospheric forcing of sea level through wind and pressure changes. However NAO and SCAN are correlated with each other during winter and they explain the same part of variability. The EA/WR also affects the atmospheric sea level component in winter (13%), acting through atmospheric pressure patterns. In winter, the thermosteric contribution is correlated with the SCAN in parts of the Eastern Mediterranean (9%). The rate of change of the thermosteric component in winter is correlated with the EA (24%). During the summer season, the sea level variance is much reduced and the impact of the large scale modes is in most parts of the Mediterranean Sea non-significant.