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A major tsunami-like event, locally known as ‘marrobbio’, impacted the southwestern coast of Sicily on 25-26 June 2014. The event was part of a chain of hazardous episodes in the Mediterranean and Black seas during the last week of June 2014 resulting from an anomalous atmospheric system (“tumultuous atmosphere”) propagating eastward over the region. The synoptic patterns and vertical structure of the atmosphere over Sicily at the time of the event indicate that atmospheric wave ducting was responsible for the generation of tsunamigenic air pressure disturbances that produced especially high sea level responses (“meteotsunamis”) at certain sites along the Sicilian coast. The strongest sea level oscillations were observed at Mazara del Vallo, where a 1-m meteotsunami bore, propagating upstream in the Mazaro River, was generated. The combined effects of external resonance (Proudman resonance on the western Sicilian shelf) and internal resonant conditions (bathymetric and topographic characteristics of specific sites) were found to be the key factors that caused the meteotsunami (marrobbio phenomenon) on the coast of Sicily and the meteobore at Mazara del Vallo. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates whether concurrent or subsequent meteotsunamis could happen at both the Balearic Islands and the Adriatic Sea as a consequence of either the simultaneous presence of the favourable synoptic pattern above both areas, or propagation of the pattern from one area to another. Meteotsunami events in sea level records from Dubrovnik (chosen to be the proxy for the occurrence of meteotsunami events in the Adriatic Sea) are compared to 32 known Ciutadella (the Balearic Islands) events. The analysis shows that a meteotsunami at the Adriatic Sea is likely to happen if the favourable synoptic pattern propagates or spreads from the Balearic Islands to the Adriatic Sea, causing meteotsunamis in both places. Upper level instabilities are recognized as the most important synoptic feature for the occurrence of meteotsunamis, as these instabilities can generate the atmospheric gravity waves which provoke meteotsunamis and also help to trap the atmospheric energy at lower levels. [Copyright &y& Elsevier]

Abstract: The paper overviews meteotsunami events documented in the Adriatic Sea in the last several decades, by using available eyewitness reports, documented literature, and atmospheric sounding and meteorological reanalysis data available on the web. The source of all documented Adriatic meteotsunamis was examined by assessing the underlying synoptic conditions. It is found that travelling atmospheric disturbances which generate the Adriatic meteotsunamis generally appear under atmospheric conditions documented also for the Balearic meteotsunamis (rissagas). These atmospheric disturbances are commonly generated by a flow over the mountain ridges (Apennines), and keep their energy through the wave-duct mechanism while propagating over a long distance below the unstable layer in the mid-troposphere. However, the Adriatic meteotsunamis may also be generated by a moving convective storm or gravity wave system coupled in the wave-CISK (Conditional Instability of the Second Kind) manner, not documented at other world meteotsunami hot spots. The travelling atmospheric disturbance is resonantly pumping the energy through the Proudman resonance over the wide Adriatic shelf, but other resonances (Greenspan, shelf) are also presumably influencing the strength of the meteotsunami waves, especially in the middle Adriatic, full of elongated islands and with a sloping bathymetry. The generated long ocean waves are hitting funnel-shaped bays or harbours of large amplification factors, resulting in meteotsunami waves with heights up to 6m at the very end of bays or harbours. Within models the mechanism is fairly well understood, but it is extremely difficult to reproduce these events (and presently almost impossible to forecast) as the meteotsunami generating process is highly variable at both temporal and spatial scales. The final part of the paper discusses the possibilities for further research of the Adriatic meteotsunamis, and meteotsunamis in general, including the basis of a meteotsunami warning system which should be able to capture potentially dangerous travelling atmospheric disturbances in real-time. [Copyright &y& Elsevier]

A destructive tsunami-like event (locally known as “rissaga” waves) occurring on 15 June, 2006 in Ciutadella Harbour (Menorca, Balearic Islands) is reproduced by a numerical model forced by a travelling atmospheric disturbance. The disturbance is reconstructed from microbarograph measurements, being the only available instrumental data at the time of the event. The model is verified based on two weaker 1997 events, which were recorded by a number of bottom pressure recorders operating at that time on the Menorca shelf, in Ciutadella Inlet and adjacent Platja Gran Inlet. Both 1997 events are numerically simulated and good agreement is achieved with observations in time, frequency (including eigenfrequencies of the affected inlets) and wave heights. Subsequently the same model is applied to simulate the 2006 event. The vigorous currents with speeds up to 400 cm/s are found to occur specifically at those areas of the harbour where the most severe damage and sinking of boats had been reported. Maximum simulated sea-level heights of 2.5 m were about one half of those reported by eyewitnesses. This difference is apparently caused by quality and spatial resolution of bathymetry data. However, in general, the model is capable of reproducing the event fairly well and can probably be used for future assessment and mitigation activities on the coasts of the Balearic Islands. [ABSTRACT FROM AUTHOR]

In engineering studies, harbor resonance, including quality and amplification factors, is typically computed for swell and waves with periods shorter than 10 min. However, in various locations around the world, such as Vela Luka Bay in Croatia, meteotsunami waves of periods greater than 10 min can excite the bay or harbor natural modes and produce substantial structural damages. In this theoretical study, the impact of some geomorphological changes of Vela Luka Bay—i.e. deepening of the bay, dredging the harbor, adding a pier or a marina—to the amplification of the meteotsunami waves are presented for a set of 6401 idealized pressure wave field forcing used to derive robust statistics. The most substantial increase in maximum elevation is found when the Vela Luka harbor is dredged to a 5 m depth, which is in contradiction with the calculation of the quality factor showing a decrease of the harbor natural resonance. It has been shown that the forcing energy content at different frequency bands should also be taken into account when estimating the quality and amplification factors, as their typical definitions derived from the peak frequency of the sea level spectrum fail to represent the harbor response during meteotsunami events. New definitions of these factors are proposed in this study and are shown to be in good agreement with the results of the statistical analysis of the Vela Luka Bay maximum elevation results. In addition, the presented methodology can easily be applicable to any other location in the world where meteotsunamis occur. [ABSTRACT FROM AUTHOR]

Abstract: A meteotsunami detection algorithm, based on real-time measurements of air pressure, was developed and tested. The algorithm consists of two modules: the first module detects potentially dangerous air pressure disturbances with tendencies exceeding a certain threshold value; the second module determines the speed and direction of propagation of those disturbances. The algorithm was tested on artificial and measured air pressure time series from three Mediterranean meteotsunami hot-spots (the Balearic Islands, the northern Adriatic, the middle Adriatic). Functionality, rapidity and reliability of two methods for determination of the air pressure disturbance’s propagation speed and direction, the isochronal analysis method and the pressure tendency method, were tested. Both methods work acceptably well, and the detection algorithm is generally able to detect potentially dangerous air pressure disturbances and to determine their speed and direction of propagation. [Copyright &y& Elsevier]

A series of meteotsunamis hit a few locations in the Mediterranean and Black Seas during 22-27 June 2014. Meteotsunamis were particularly numerous on 25 and 26 June in the Adriatic Sea, where at least six harbours and bays were stricken by powerful waves: strongest events occurred in Vela Luka (Korčula Island), a known meteotsunami hot-spot, where waves reached height of ~3 m, and in Rijeka dubrovačka Bay, where strong ~5 m/s currents accompanied ~2.5 m high waves. Intensification of high-frequency sea level activity was observed at both the eastern and western Adriatic tide gauge stations, with maximum recorded wave heights reaching ~68 cm (Ortona, Italy). A series of individual air pressure disturbances characterized by pronounced rates of air pressure change (up to 2.4 hPa/5 min), limited spatial extent (~50 km) and high temporal variability, propagated over the Adriatic on 2 days in question. Numerical hydrodynamic model SCHISM forced by measured and idealised air pressure disturbances was utilised to reproduce the observed Adriatic sea level response. Several important conclusions were reached: (1) meteotsunamis occurring at various parts of the coast were generated by different atmospheric air pressure disturbances; (2) topographic influence can be removed from sea level spectra by computing spectral signal-to-background ratios; the result, being related to the external forcing, resembles atmospheric pressure spectra; (3) sea response is strongly dependant on details of atmospheric forcing; and (4) over complex bathymetries, like the middle and south Adriatic ones, numerous effects, including Proudman resonance, edge waves, strong topographical enhancement and refractions on the islands placed on the pathway of atmospheric disturbances should be taken into account to fully understand meteotsunami generation and dynamics. An in-depth numerical study is planned to supplement the latter conclusion and to quantify contribution of each process. [ABSTRACT FROM AUTHOR]

This paper provides global climatology of high-frequency (T < 2 h) sea-level oscillations of atmospheric origin. Sea-level series with a temporal resolution of 1 min from 331 tide gauges in the world ocean and spanning between 1.5 and 12 years were analysed to determine the typical ranges, seasons and characteristics of moderate and extreme manifestations of nonseismic sea-level oscillations at tsunami timescales (NSLOTTs). Variances in these oscillations reach 6.6 cm2 on average, but their region-averaged extreme (99.99th percentile) ranges may exceed half a metre or more at individual hotspot locations. The NSLOTTs are the highest in the mid-latitudes and decrease towards polar and tropical regions. Moderate oscillations show clear winter maxima at the majority of stations, while a less pronounced pattern is evident for the most extreme oscillations, which may occur throughout a year. A total of 3080 of the most prominent NSLOTT events were selected from 308 stations and compared to background oscillations, revealing the substantial capability of energy amplification during extreme events. Synchronicity in extreme NSLOTT events between neighbouring stations (up to 250 km) in mid-latitudes has been detected for 20–32% of all episodes, suggesting possible connectivity between the episodes. • Nonseismic sea-level oscillations at tsunami timescales have small variances. • However, their ranges may exceed half a metre in some regions and locations. • The oscillations are highest in the mid-latitudes. • Moderate oscillations have winter maxima, extreme oscillations occur through a year. • Extreme oscillations are synchronous in one fourth of occurrences in mid-latitudes. [ABSTRACT FROM AUTHOR]