Trends and interannual oscillations in the main sea-level surface pressurepatterns over the Mediterranean, 1955-1990

The evolution of the main sea level pressure patterns built from Rotated Pr incipal Component Analysis (RPCA) over a domain centered on the Mediterrane an for the period 1955-1990 is examined. The annual cycle and the interannu al variations are analyzed using Singular Spectrum Analysis (SSA) and three methods of spectral analysis, to detect trends and oscillations in the mai n patterns. The dominant patterns show oscillations characteristic of NAO a nd SO. This paper shows that NAO and SO seem to be correlated in a band cen tered in 6-8 years and that SLP behaviour over the region is dominated by Q BO (which controls the oscillation frequency) while NAO modulates the ampli tudes.