Synoptic conditions for the generation of meteotsunamis on the shelf of the northwestern Black Sea region and in the Azov Sea

An analysis of the causes of the occurrence of meteotsunamis, which were registered on May 7, 2007 on the northern part of the Bulgarian coast, on June 14, 2014 in the Odessa region and in the Ilyichevsk (Chernomorsk) port (Sukhoi Estuary), on July 19, 2017 in the waters of the Belosarayskaya Spit in Azov, showed that all these phenomena occurred under similar macroscale synoptic conditions situations over south-eastern Europe.

At the same time, the required morphometric conditions were present at the points of meteotsunami recording: a low rate of depth decrease towards the coast, the location and structure of the coast in all three cases suggested the possibility of a long sea wave arriving from the open sea from a distance of 130-200 km and, accordingly, the occurrence of Proudman resonance. In all cases, the local nature of the phenomenon was noted: the length of the wave crest along the front did not exceed several tens of kilometers.

Analysis of the maps of the high-altitude geopotential (850 and 500 hPa) for the Azov-Black Sea region on the indicated dates shows a classic picture of the frontal interaction between the Asia Minor Depression (with dry and very warm air of African origin) and the cold and humid (polar) air of the anticyclone over Eastern Europe. Such fronts are a source of atmospheric instability and wind strengthening at all levels.

A comparative analysis of synoptic maps for the above dates showed a fairly good qualitative correspondence between the structure of surface pressure fields and the location of fronts; satellite information also showed the presence of zones of powerful convective cloudiness over the Azov-Black Sea region. An important feature of the synoptic situation is the instability line over the western or central parts of the Black Sea, which indicates the presence of a ridge of cumulonimbus clouds (Cb) and the existence of powerful convective movements that can reach the stratosphere - overshotting helps replenish the energy of jet streams. This structure and state of the atmosphere was defined by A. Rabinoviches and J. Šepić with the general term – a "tumultuous atmosphere". Thunderstorm phenomena characteristic of Cb are capable of generating a wide range of internal gravity waves with characteristic periods from 3 to 60 minutes.

The analyzed synoptic conditions during the tsunami were completely favorable for the occurrence and propagation of a possible moving atmospheric gravity disturbance. In all three cases, the Froude number was close to unity, indicating that the conditions for the Proudman resonance were met.

 Thus, the combination of synoptic and geographical factors indicates a significant probability of this phenomenon occurring only in certain areas of the Azov-Black Sea region: the western shelf of the northwestern part of the Black Sea, including relatively deep-water estuaries, and the Belosarayskaya Spit area of ​​the Azov Sea.