Wind versus air pressure seiche triggering in the Middle Adriatic coastal waters

Strong air pressure and sea level oscillations, which occurred in the Middle Adriatic region during the storm passage on 21 August 2004, were recorded at a number of meteorological and tide gauge stations. Large sea levels measured were related to the Proudman and harbour resonances, being also observed during the past event on 27 June 2003. Both cases were characterized by a travelling air pressure disturbance, but a part of the oscillations in August 2004 case were a result of short-lasting strong winds which were absent during the event in June 2003. Occurrence of a strong 4-h fundamental oscillation of the whole region versus weak harbour seiches was a result of the shape of travelling air pressure disturbance: it looked like a box-function containing large energies in a low frequency domain, whereas the event in June 2003 was characterized by a cosine-like disturbance, redistributing the energy towards higher frequencies. Using a numerical model it is shown that the strength of 4-h oscillation is sensitive to the speed of travelling atmospheric disturbance and to its incoming direction. The largest amplitudes were modelled for a speed of 13 m/s, indicating that inner part of the region is possibly the best place for occurrence of the Proudman resonance.