Source of the 2007 Ist meteotsunami (Adriatic Sea)

Abstract

Široka Bay on the island of Ist in the northern Adriatic was struck by a severe inundation around 1530 UTC on 22 August 2007. The maximum wave height reached 4 m, and substantial material damage was induced. This paper investigates the generating force of the inundation. Data analysis indicates that the inundation was provoked through a double resonance mechanism, with initiation by a pronounced atmospheric disturbance that generated open ocean waves through the Proudman resonance. The waves were then further amplified inside the affected bay. The air pressure disturbance, which propagated at a speed of about 21–24 m s−1 over the northern Adriatic shelf, was investigated through both data analysis and atmospheric numerical modeling. Apparently, the air pressure disturbance was a surface manifestation of a ducted gravity wave, which propagated through the atmosphere from the Apennines to the eastern Adriatic coast over the northern Adriatic. According to the model simulation, the wave was trapped in a stable layer adjacent to the ground, which was capped by a dynamically unstable layer with wind speeds of about 22 m s−1. This made the unstable layer also a critical layer for gravity waves propagating with the same speed and allowed for their ducting in the layer below.