A Chain of Destructive Meteotsunamis Occurred in the Mediterranean Region on 23-27 June, 2014

Abstract:

A number of tsunami like events occurred in the Mediterranean and the Black Sea during 23 to 27 June 2014. First location to be struck was Ciutadella harbor (the Balearic Islands, Spain), where 1-m high oscillations were observed in the early morning hours of 23 June. Two days later (25 June), during morning to afternoon hours, four bays in the Adriatic Sea were hit by tsunami waves with wave-heights of up to 3 m. These waves were accompanied by strong destructive currents. The same day, a phenomenon locally known as "marrobbio" occurred on the western coast of Sicily: a strong tidal bore with wave heights of >1.5 m propagated inside the Mazara River inlet, damaging moored vessels. Finally, at the midday of 27 June, a sudden tsunami-like wave swept beaches in Odessa, the Black Sea (Ukraine) injuring a number of beach-goers. All of these events were associated with abrupt air pressure changes of > 2 hPa/5 min), and may be classified as meteorological tsunamis. Analysis of troposphere conditions revealed that this chain of events has a mutual origin and is related to a unique synoptic system which traversed the Mediterranean and the Black Sea during 23-27 June 2014. The pattern was characterized by: (i) weak surface cyclone; (ii) an inflow of a warm and dry African air at heights of ~850 hPa, (iii) very strong southern-southwestern mid-troposphere jet stream (wind speeds of 20-40 m/s) which was (iv) embedded into unstable atmospheric layers at heights of 700-400 hPa. Described conditions support generation and trapping of atmospheric gravity waves (whose surface manifestation are distinct air pressure disturbances) at a forefront of a jet stream. Trapped atmospheric gravity waves are "transported" by the jet stream, thus propagating with its speed and direction. Mapping of Froude number, Fr = U/c, where U is the jet stream speed, and c is the long-wave speed, and analysis of events and tide-gauge records indicated that strongest sea level oscillations were observed at resonant areas for which Fr ~ 0.9-1.1.