The "Mad Sea" phenomenon in the strait of Sicily

Sea level observations at Cape Bon, Tunisia, and Mazara del Vallo, Sicily, show that large, coherent oscillations exist across the Strait of Sicily wi th significant energy bands centered at periods of 35.3, 41.6, 50.6, 75.8, and 134.5 min, whose possible structure is confirmed by a numerical approxi mation to the gravitational barotropic normal modes with realistic topograp hy. It is observed that these oscillations are related to the passage of sy noptic weather systems over the region. An investigation on the configurati on, phase velocity, and direction of approach of atmospheric disturbances o ver the region suggests that the oscillations in the Strait of Sicily could be forced by instabilities that develop in large-scale, low pressure front s that propagate as pressure gravity waves with an approximate phase speed between 24 and 30 m s(-1).