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From 12 to 16 October 2016, a series of three strong low-pressure systems, including typhoon “Songda”, passed over the coasts of southern British Columbia (BC) and Washington State (WA). Typhoon “Songda” was generated on 2 October about 1,000 miles to the southwest of Hawaii. After passing along the coast of Japan, it turned eastward, crossed the Pacific Ocean, arriving off the coast of North America on 12 October, where it merged with local extratropical cyclones propagating along the coast of Vancouver Island. These three lows passed across the western coast of the island on 14-15 October, generating strong surface currents if the offshore region and significant sea level oscillations, including storm surges, seiches and infragravity waves along southern BC and northern Washington. Oceanic observations of the event included HF WERA radar data, offshore bottom sea pressure measurements from the Ocean Network Canada (ONC) observatories and sea level records from BC and WA tide gauges. Meteorological data analyzed included radar records, satellite imaginary, reanalysis synoptic data, and air pressure and wind surface measurements of remarkable spatial and temporal resolution from more than 150 school network stations. These extensive datasets allowed for a detailed tracking of atmospheric processes responsible for strong ocean surface currents and sea-level oscillations. Maximum currents of up to 50 cm/s were measured by the HF radar. The surge heights on the southern BC and northern WA coasts were higher than 80 cm, with maximum storm surge observed at La Push, WA (117 cm) and New Westminster, BC (101 cm). A particularly interesting phenomenon was observed on the west side of Vancouver Island, beginning at Tofino, where the tide gauge record indicated a sharp, knife-like 40-cm increase in sea level with a peak value at 07:01 UTC on 14 October. Slightly lower sharp sea level peaks were also observed at Bamfield, Port Alberni and Port Renfrew. The high negative correlation between sea level and atmospheric pressure is consistent with the inverted barometer (IB) effect. Sharp sea level peaks at Tofino, Bamfield and Port Alberni are shown to be related to the specific shapes of the air pressure variations at these sites (the minimum atmospheric pressure at Tofino was 971.4 hPa), but the sea level response was 1.5-2.5 times greater than the IB effect, demonstrating the topographic amplification of sea levels in the respective areas. Such oscillations at Tofino and surrounding regions, may be described as a “meteorological tsunami” that for this specific case has a character of a forced solitary wave.

In this study, an analysis of the observed Adriatic mean sea level time series has been carried out in order to determine the primary causes of the changes documented during the last 50 years. Monthly sea level data were downloaded from the Permanent Service for Mean Sea Level for seven stations located along the northern and eastern Adriatic coast: Venice, Trieste, Rovinj, Bakar, Zadar, Split and Dubrovnik. Significant positive sea level trend, related to climate change, was detected at the majority of the stations. Further on, using Rodionov’s regime shift index algorithm, several regime shifts were detected. The first pronounced regime shift occurred in 1989 resulting with mean sea level lower than usual for an average of 4.37 cm; the second regime shift occurred in 1996 when mean sea level increased for an average of 2.07 cm; and the third regime shift, which is still on-going, started in 2009 when mean sea level abruptly increased to 5.3 cm above average. A relationship between North Atlantic Oscillation (NAO) and sea level data has been explored, using both monthly and yearly data. High and significant correlation between the two was established for all data, and in particular for the winter season (December, January, February, March). All climate shifts were related to pronounced changes of NAO. The negative shift starting in 1989 was related to the positive phase of NAO, i.e. to weaker cyclonic activity over the Mediterranean and the Adriatic Sea. Oppositely, the two latter positive regime shifts were related to significant decrease and negative phases of NAO, with NAO reaching the most negative values of the entire observation period during the shift starting in 2009. Negative phase of NAO corresponds to stronger cyclonic activity over the Mediterranean and the Adriatic Sea. In conclusion, documented rise of the Adriatic sea level during the last 50 years, and in particular accelerated rise during the last 20 years represent a combination of mean sea level rise due to climate change and due to atmospherically induced shift of climate regimes.

Extreme sea levels can lead to floods that cause significant damage to coastal infrastructure and put people's lives in danger. These floods are a result of physical processes occurring at various time and space scales, including sub-hourly scales. To estimate the contribution of sub-hourly sea level oscillations to extreme sea levels, raw sea level data from about 300 tide gauge stations along the European coasts, with a sampling resolution of less than 20 minutes, were collected. The data were obtained from: (1) the IOC-SLSMF website (290 stations); (2) National agencies (Portugal, Finland, Croatia –24 stations). Portions of the raw dataset had various data quality issues (i.e., spikes, shifts, drifts) hence quality control procedure was required. Out of range values, values with a 50 cm difference from one neighbouring value or a 30 cm difference from both neighbouring values, were automatically removed. The automatic spike detection procedure was carried out by removing values that differed by three standard deviations from a spline fitted with the least squares method. Following the automatic quality control, all remaining data were visually examined and spurious data were removed manually.The resulting data set contains sea level data from 2007. to 2021., with an average record length of approximately 7 years, however the length varies from a few months at some stations to 13 years at others. Tide gauges with longer records (>10 years) are based in the Baltic region, France and Spain, whereas the ones with shorter records (Preliminary statistical analyses were done, resulting with spatial and temporal distribution of contribution of high-frequency sea level oscillations to total sea level extremes along the European coasts.

Six young oceanographers (authors of this article), all working at the science institutions in Split (Croatia), connected closely through their work on SHExtreme and StVar-Adri projects. The members of the group previously had, in total, over 30 years of experience in organization and participation in voluntary popular science and educational activities, e.g., Science Festival, Science Factory, FantaSTikon. However, most of this was done in the large cities and at the mainland.Partly motivated by the “science to all” idea, during 2021 the group had the vision of bringing ocean science to the inhabitants of the Adriatic Sea islands (hours distant to the large cities, having low number of daily connections, with low-count and prevailingly older population), especially children. Their aim was to offer various educational, science-promotive and fun extracurricular activities (main topic being sea) to the islanders, as these activities were rare even in pre-pandemic times and became almost non-existent during 2020/2021.Thus, during the summer of 2021 “Oceanographers at the Island” held a series of events at three middle Adriatic Islands (Korčula, Ugljan and Hvar). The events included oceanographic science and art workshops for younger (6-10 years) and older (10-14 years) children, sea-topic boardgame gatherings and public talks at local cafes. During the workshops the children have done experiments and meteorological and oceanographic in-situ measurements, followed by the discussions and conclusions on the phenomena. As a result attendees have broadened their knowledge on the thermohaline properties and processes, sea motion and atmosphere-sea interaction. Highly incentive for the children to attend the workshops, selected (board)games, with topics of sea-ecology-strategy, made them revise their knowledge on the sea ecosystem while having fun and feel they, as humans, have an important impact of the present-and-future of their sea-oriented community and the planet. As a commune final product the attending children made posters and picture plates with the messages they found the most important and these were exhibited at the highest visibility places in their community (school or tourist information centre). To strengthen their remembrance on the events and “promises made to the sea” and motivating future science inclusion children were awarded by “The little oceanographer” diploma. General public talks, different at each location, presented an issue of interest for islanders of that particular island. In Vela Luka on Korčula, the topic was a devastating Great Vela Luka flood of 1978 which brought severe destruction to the island, in Vrboska on Hvar, topic were “schigas” – a local phenomenon of sudden sea level oscillations specific for that village; and in Ugljan on Ugljan topic was climate change – of especial interest to community given the numerous natural disasters which occurred during the summer of 2021.All events were covered by local media (including newspapers, radio, web portals and social networks), and the entire initiative was presented to public by national media. Being praised by the locals and visitors from all age groups, the “Oceanographers at the islands” are continuing their “The sea talks to us, let’s listen to it!” work at new locations in 2022.

Sea level time series of up to 19 years length, recorded with one-minute sampling interval at 18 tide gauges, evenly distributed along the eastern and western coast of the Adriatic Sea, were analysed in an attempt to quantify hazard related to the Adriatic Sea level extremes. Prior to analysis, quality control and pre-processing were done: all unphysical spikes and outliers were removed; shorter gaps were interpolated, and time series were de-tided.For each tide gauge, two types of sea level extremes were defined and extracted from residual time series: (1) extremes related to storm surges, i.e. extremes that dominate the total residual signal; (2) extremes related to meteotsunamis, i.e. extremes that dominate the high-frequency signal (T < 2 h). The two types of extremes were analysed in detail and following conclusions were reached: (1) on average, extremes related to storm surges are stronger than those related to meteotsunamis; (2) nonetheless, there are stations at which two types of extremes are of almost comparable strength (e.g. Vela Luka, Stari Grad); (3) high-frequency oscillations can contribute significantly (up to 30% of residual signal) to the storm surge related extremes at most areas; (4) extremes related to storm surges mostly happen from October to January while the second type of extremes happen more throughout the year, with peak appearances of the strongest ones from May to September. Conclusively, for both types of episodes, it has been shown that the high-frequency signal contributes significantly to total extremes and that analysis of sea level time series sampled at a one-minute time interval is a prerequisite for proper analysis of hazards related to sea level extremes.

Special issue “Advances in interdisciplinary studies at multiple scales in the Mediterranean Sea”. It is a result of the 8th MONGOOS Meeting & Workshop, Trieste, Italy, 3–5 December 2019.-- 57 pages, 9 figures, 1 table, 1 appendix, supplement https://doi.org/10.5194/os-18-997-2022-supplement.-- Data availability: Access to sea level data presented in this review is provided through national and international data portals and repositories quoted in Sects. 2 and 3 and in the Supplement, Employed for over a century, the traditional way of monitoring sea level variability by tide gauges – in combination with modern observational techniques like satellite altimetry – is an inevitable ingredient in sea level studies over the climate scales and in coastal seas. The development of the instrumentation, remote data acquisition, processing, and archiving in the last decades has allowed the extension of the applications to a variety of users and coastal hazard managers. The Mediterranean and Black seas are examples of such a transition – while having a long tradition of sea level observations with several records spanning over a century, the number of modern tide gauge stations is growing rapidly, with data available both in real time and as a research product at different time resolutions. As no comprehensive survey of the tide gauge networks has been carried out recently in these basins, the aim of this paper is to map the existing coastal sea level monitoring infrastructures and the respective data availability. The survey encompasses a description of major monitoring networks in the Mediterranean and Black seas and their characteristics, including the type of sea level sensors, measuring resolutions, data availability, and existence of ancillary measurements, altogether collecting information about 240 presently operational tide gauge stations. The availability of the Mediterranean and Black seas sea level data in the global and European sea level repositories has been also screened and classified following their sampling interval and level of quality check, pointing to the necessity of harmonization of the data available with different metadata and series in different repositories. Finally, an assessment of the networks' capabilities for their use in different sea level applications has been done, with recommendations that might mitigate the bottlenecks and ensure further development of the networks in a coordinated way, a critical need in the era of human-induced climate changes and sea level rise, This research has been partially supported by Horizon 2020 (EuroSea (grant no. 862626) and JERICO-S3 (grant no. 871153)), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

Typhoon Maysak (Julian in the Philippines) was a powerful tropical cyclone that strongly impacted coastal regions of the Sea of Japan on 2–4 September 2020. Destructive winds, violent storm waves, and intense rainfall occurred in Japan, on the Korean Peninsula, and in Far-Eastern Russia. Devastating coastal floods caused severe damage to coastal infrastructure and to ships and boats anchored in harbours and were responsible for numerous deaths. Our study indicates that the main reason for the destructive floods was the superposition of storm surge, extreme seiches (meteorological tsunamis), and surf beats. At various sites, different types of sea level oscillations prevailed depending on the atmospheric forcing, local topographic properties, and resonant shelf/coastal zone features. The principal forcing factors of these oscillations were atmospheric pressure and wind stress, but the exact generation mechanism of each specific type of oscillation was strongly site dependent. The uniqueness of the sea level response at each site is the main challenge in our understanding of the generation process and to the mitigation of the hazardous consequences of possible future events.

The meteotsunami early warning system prototype using stochastic surrogate approach and running operationally in the eastern Adriatic Sea is presented. First, the atmospheric internal gravity waves (IGWs) driving the meteotsunamis are either forecasted with state‐of‐the‐art deterministic models at least a day in advance or detected through measurements at least 2 hr before the meteotsunami reaches sensitive locations. The extreme sea‐level hazard forecast at endangered locations is then derived with an innovative stochastic surrogate model—implemented with generalized polynomial chaos expansion (gPCE) method and synthetic IGWs forcing a barotropic ocean model—used with the input parameters extracted from deterministic model results and/or measurements. The evaluation of the system, both against five historical events and for all the detected potential meteotsunamis since late 2018 when the early warning system prototype became operational, reveals that the meteotsunami hazard is conservatively assessed but often overestimated at some locations. Despite some needed improvements and developments, this study demonstrates that gPCE‐based methods can be used for atmospherically driven extreme sea‐level hazard assessment and in geosciences in wide.

Sea-level observations provide information on a variety of processes occurring over different temporal and spatial scales that may contribute to coastal flooding and hazards. However, global research of sea-level extremes is restricted to hourly datasets, which prevent quantification and analyses of processes occurring at timescales between a few minutes and a few hours. These shorter period processes, like seiches, meteotsunamis, infragravity and coastal waves, may even dominate in low-tidal basins. Therefore, a new global 1-minute sea-level dataset – MISELA (Minute Sea-Level Analysis) – has been developed, encompassing quality-checked records of nonseismic sea-level oscillations at tsunami timescales (T https://doi.org/10.14284/456, Zemunik et al., 2021b). This paper describes data quality-control procedures applied to the MISELA dataset, world and regional coverage of tide-gauge sites and lengths of time-series. The dataset is appropriate for global, regional or local research of atmospherically-induced high-frequency sea-level oscillations, which should be included in the overall sea-level extremes assessments.

Two hazardous typhoons, Maysak and Haishen, in September 2020 produced extreme sea level oscillations in the Sea of Japan. These typhoons generated three different types of sea level variations: 1) storm surges (with typical periods from several hours to 1.5 days), 2) extreme seiches (with periods from a few minutes to several tens of minutes), and 3) storm-generated infragravity waves (with periods up to 3-5 min). The data from eleven tide gauges on Russian, Korean, and Japanese coasts were used to examine the properties of these oscillations. The relative contribution of the three separate sea level components and their statistical characteristics (duration, wave heights, and periods) were estimated. The periods of the main eigen modes of individual bays and harbours in the Sea of Japan were estimated based on spectral analysis of longterm background records at the corresponding sites. The results of wavelet analysis show the frequency properties and the temporal evolution of individual sea level components. We found that high-frequency sea level oscillations at stations Preobrazheniye and Rudnaya Pristan have a “white noise” spectrum, caused by the dominance of infragravity waves. A high correlation was detected between the variance of high-frequency sea level oscillations at these stations and the significant wind wave height evaluated from ERA5 for this water area.

The Adriatic Sea is known to be under a high flooding risk due to both storm surges and meteorological tsunamis, with the latter defined as short-period sea-level oscillations alike to tsunamis but generated by atmospheric processes. In June 2017, a tide-gauge station with a 1-min sampling resolution has been installed at Stari Grad (middle Adriatic Sea), the well-known meteotsunami hot-spot, which is, also, often hit by storm surges. Three years of corresponding sea-level measurements were analyzed, and 10 strongest episodes of each of the following extreme types were extracted from the residual series: (1) positive long-period (T > 210 min) extremes; (2) negative long-period (T > 210 min) extremes; (3) short-period (T < 210) extremes. Long-period extremes were defined as situations during which sea level surpasses (is lower than) 99.7 (i.e. 2) percentile of sea level height, and short-period extremes as situations during which variance of short-period sea-level oscillations is higher than 99.4 percentile of total variance[J1] of short-period series. A strong seasonal signal was detected for all extremes, with most of the positive long-period extremes appearing during November to February, and most of the negative long-period extremes during January to February. As for the short-period extremes, these appear evenly throughout the year, but strongest events seem to appear during May to July.All events were associated to characteristic atmospheric situations, using both local measurements of the atmospheric variables, and ERA5 Reanalysis dataset. It was shown that positive low-pass extremes commonly appear during presence of low pressure over the Adriatic associated with strong SE winds (“sirocco”), and negative low-pass extremes are associated to the high atmospheric pressure over the area associated with either strong NE winds (“bora”), or no winds at all. On the other hand, high-pass sea level extremes are noticed during two distinct types of atmospheric situations corresponding to both “bad” (low pressure, strong SE wind) and “nice” (high pressure, no wind) weather.It is particularly interesting that short-period extremes, of which strongest are meteotsunamis, are occasionally coincident with positive long-period extremes contributing with up to 50 percent to total sea level height – thus implying existence of a double danger phenomena (meteotsunami + storm surge).

The paper presents sea level and air pressure observations acquired during the 2007 experiment carried out along the southwestern coast of Sicily. The experiment aimed to quantify the atmospheric and oceanic conditions related with the phenomenon of marrobbio, a kind of meteotsunami that is frequently observed in the Strait of Sicily. Sea level data measured at surrounding tide gauges, radio-sounding atmospheric profiles and ERA5 reanalysis data conjoined the analysis. Rapid air pressure and sea level oscillations were measured simultaneously during marrobbio events, while the atmospheric disturbances were estimated to propagate mostly towards east- northeast with a predominant speed of 19–24 m/s. The observed propagation direction and speed were found conducive for generation of long ocean waves through Proudman resonance over a wide outer shelf, although a complex bathymetry in front of affected area may strongly modify the generation. The atmospheric patterns were favourable for wave ducting mechanism during most of the observed marrobbio events. A need for establishing long-term high frequency observations at marrobbio hot spots, as well to apply high-resolution atmospheric and oceanic models for proper quantification of meteotsunamis, is emphasized.

Tsunami-like sea level oscillations recently recorded by tide gauges located along the coasts of British Columbia (Canada) and Washington State (USA) have been identified as meteorological tsunamis. Globally, such events can create hazardous conditions in coastal areas, including the possible loss of life, and need to be taken into account in any assessment of risk to nearshore infrastructure. On 1 November 2010, a significant meteotsunami occurred in the southern Strait of Georgia, British Columbia. To examine this event, we have used all available sea level and air pressure data, including 1-min records from five Canadian Hydrographic Service and five USA National Oceanic and Atmospheric Administration tide gauges, as well as high-resolution time series from two Ocean Network Canada VENUS bottom pressure recorders and from 132 air pressure sensors within the Victoria School-Based Weather Station Network of southern British Columbia. The oceanic responses to four well-defined atmospheric disturbances (labelled D1–D4) were selected for analysis. Disturbance D3, which propagated toward ~ 100° True (eastward) at a speed of ~ 20 m/s, appears to have been responsible for generating the meteotsunami observed in the southern Strait of Georgia, while disturbance D4 that moved toward ~ 55° True at a speed of 24 m/s appears to have produced the meteotsunami observed in Juan de Fuca Strait that separates Vancouver Island from Washington State. We used the physical parameters derived for the four disturbances to force numerical simulations of the events and compared the results to observations from selected tide gauge sites. The numerical experiments revealed strongly individual sea level responses at each site to changing air pressure disturbance speed, direction and intensity, such that each location has its own set of “site-specific” air pressure characteristics that produce the strongest sea level response. Differences in the local topography and coastline geometry appear to be responsible for the different responses among sites.

Meteorological tsunamis are frequently destructive tsunami-like waves generated by small-scale atmospheric disturbances. Several devastating events occurred recently in various regions of the world oceans, including the Balearic Islands, Sicily, the Adriatic and Black seas, the Great Lakes, the west coast of South Korea, the Netherlands and the Persian Gulf. Although this phenomenon has been actively studied for more than 25 years, the exact mechanism (or mechanisms) responsible for producing these extreme events remains a puzzle. One of the major problems making it difficult to determine the physical process generating meteotsunamis is the absence of a network of simultaneously working precise tide gauges and microbarographs in the affected region. A unique set of high-resolution atmospheric data from the meteorological “school network” of 132 school stations became available for 2008-2019 for the area of southern Vancouver Island and nearby Gulf Islands located in the Strait of Georgia. These data, combined with 1-min sea level data from Canadian Hydrographic Service (CHS) and USA National Oceanic and Atmospheric Administration (NOAA) tide gauges, has enabled us to examine both the spatial and temporal features of mesoscale atmospheric disturbances and coincident properties of the associated sea level oscillations. The data analyses, supported by a series of numerical experiments, has made it possible to reconstruct observed events and to determine the specific atmospheric parameters producing the strongest sea level response in the southern part of the Strait of Georgia. These experiments have helped us to recognize the most effective (and hence, most hazardous) directions and speeds of propagating atmospheric disturbances and to identify “hot spots” along the coast that are under the highest risk of large meteotsunamis.

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.

On 27 June, a 1–2-m high wave struck the beaches of Odessa, the third largest Ukrainian city, and the neighbouring port-town Illichevsk (northwestern Black Sea). Throughout the day, prominent seiche oscillations were observed in several other ports of the Black Sea. Tsunamigenic synoptic conditions were found over the Black Sea, stretching from Romania in the west to the Crimean Peninsula in the east. Intense air pressure disturbances and convective thunderstorm clouds were associated with these conditions ; right at the time of the event, a 1.5-hPa air pressure jump was recorded at Odessa and a few hours earlier in Romania. We have utilized a barotropic ocean numerical model to test two hypotheses: (1) a tsunami-like wave was generated by an air pressure disturbance propagating directly over Odessa (‘‘Experiment 1’’) ; (2) a tsunami-like wave was generated by an air pressure disturbance propagating offshore, approximately 200 km to the south of Odessa, and along the shelf break (‘‘Experiment 2’’). Both experiments decisively confirm the meteorological origin of the tsunami- like waves on the coast of Odessa and imply that intensified long ocean waves in this region were generated via the Proudman resonance mechanism while propagating over the northwestern Black Sea shelf. The ‘‘Odessa tsunami’’ of 27 June 2014 was identified as a ‘‘beach meteotsunami’’, similar to events regularly observed on the beaches of Florida, USA, but different from the ‘‘harbour meteotsunamis’’, which occurred 1–3 days earlier in Ciutadella (Baleares, Spain), Mazara del Vallo (Sicily, Italy) and Vela Luka (Croatia) in the Mediterranean Sea, despite that they were associated with the same atmospheric system moving over the Mediterranean/Black Sea region on 23–27 June 2014.

The paper provides a comprehensive review of all aspects of Adriatic Sea level research covered by the literature. It discusses changes occurring over millennial timescales and documented by a variety of natural and man-made proxies and post- glacial rebound models ; mean sea level changes occurring over centennial to annual timescales and measured by modern instruments ; and daily and higher-frequency changes (with periods ranging from minutes to a day) that are contributing to sea level extremes and are relevant for present-day flooding of coastal areas. Special tribute is paid to the historic sea level studies that shaped modern sea level research in the Adriatic, followed by a discussion of existing in situ and remote sensing observing systems operating in the Adriatic area, operational forecasting systems for Adriatic storm surges, as well as warning systems for tsunamis and meteotsunamis. Projections and predictions of sea level and related hazards are also included in the review. Based on this review, open issues and research gaps in the Adriatic Sea level studies are identified, as well as the additional research efforts needed to fill the gaps. The Adriatic Sea, thus, remains a laboratory for coastal sea level studies for semi-enclosed, coastal and marginal seas in the world ocean.

The paper documents seasonality, interannual-to-decadal variability, and trends in temperature, salinity, and density over a transect in the shallow northern Adriatic Sea (Mediterranean Sea) between 1979 and 2017. The amplitude of seasonality decreases with depth and is much larger in temperature and density than in salinity. Time series of temperature and salinity are correlated in the surface but not in the bottom layer. Trends in temperature are large (up to 0.6 ∘C over 10 years), significant through the area, and not sensitive to the sampling interval and time series length. In contrast, trends in salinity are largely small and insignificant and depend on the time series length. The warming of the area is more during spring and summer. Such large temperature trends and their spatial variability emphasize the importance of maintaining regular long-term observations for the proper estimation of thermohaline trends and their variability. This is particularly important in regions which are key for driving thermohaline circulation such as the northern Adriatic, with the potential to affect biogeochemical and ecological properties of the whole Adriatic Sea.

A performance study of seven regional ocean configurations based on NEMO has been carried out for the Adriatic Sea over a common period (1980–2012). Assessed models differ in resolution, model physics, atmospheric forcing (forced vs. coupled models) and river discharges imposed within the Adriatic Sea. Models have been evaluated on the long-term temperature and salinity measurements in all of the Adriatic sub-basins, in particular within dense water collectors (Jabuka Pit and South Adriatic Pit) and dense water formation sites (northern and southern Adriatic). Adriatic-wide salinity content is mostly linked to the proper introduction of the overall water budget, rather than to the local river forcing. Forced models mostly overestimate temperature and salinity values. On average, coupled models better reproduce the thermohaline properties and processes, in particular the Adriatic-Ionian Bimodal Oscillating System (BiOS) reversals and its decadal variability. Wintertime heat losses are playing major role in defining the Adriatic Deep Water (ADW) transport rates in coupled models, while in forced models preconditioning in salinity is the most important factor. Further on, increase of resolution of the atmospheric forcing results in more realistic ocean behaviour, including dense water formation (DWF) in the complex coastal northern Adriatic. However, all models have large temperature biases and lower deep stratification at the dense water collector sites, indicating overall underrepresentation of the Adriatic DWF. Consequently, mixed-layer depth in the southern Adriatic is overestimated, reaching the bottom during some years. Ocean model resolution and river forcing seem to play a second-order role in defining the overall Adriatic-Ionian thermohaline properties, while inclusion of aerosol trend only slightly modified the BiOS reproduction., One simulation was performed using HPC resources from GENCI-[TGCC/CINES/IDRIS], Grant 0227). AVISO+ product were downloaded from https://www.aviso.altimetry.fr. This work is a part of the Med-CORDEX initiative (www.medcordex.eu) and a contribution to the MISTRALS/HyMeX programme. The support from Croatian Science Foundation is acknowledged through projects ADIOS [HRZZ grant IP-06-2016-1955] and SCOOL [HRZZ grant IP-2014-09-5747].

This paper documents the analysis of a coastal boulder deposit that was recently identified along the northern Adriatic coast (Premantura Promontory, Istria, Croatia). Accumulations of large boulders have not previously been reported in the northern Adriatic, which can be viewed as a semi-enclosed basin. A multidisciplinary approach was used to investigate the site including geological and geomorphological surveys, together with the use of an Unmanned Aerial Vehicle (UAV), digital photogrammetric analysis, hydrodynamic modelling and 14C AMS datings. Measurements of boulder position, elevation, size, shape and density were fed into hydrodynamic equations that are used to estimate the minimum storm and tsunami wave height required to enable the accumulation of boulders. Biogenic marine carbonate encrustations observed on 14 boulders suggest the infra- and sublittoral zones as source areas, while for most of the boulders a subaerial origin is hypothesised. The boulder deposit occurs on a flat promontory where the topography, together with the stratified limestone bedding planes and dense joint pattern constitute the predisposing factors for boulder size and detachment. Comparisons between satellite images taken between 2008 and 2017, pictures collected from Internet and a 2012 snorkel survey of the Istrian coast made it possible to highlight the emplacement of a boulder with an estimated weight of 7.65 t during late 2013 or early 2014. The study examines the mechanisms that may be responsible for the detachment and transport of these large limestone rock fragments from the emergent part of the coast and from the sea bed towards inland areas. The results suggest the occurrence of very recent extreme weather conditions as well as multiple historical storm events and exclude a tsunami origin of the boulders.

On 19 March 2017, destructive tsunami-like waves impacted the northeast shore of the Persian Gulf (PG). The maximum surveyed runup of about 3 m was observed at Dayyer in southern Iran, where damaging waves inundated the land for a distance of * 1 km and resulted in the deaths of five people. Because the PG has always been considered safe from extreme oceanic waves, the event was totally unexpected. In this study, we examined sea level data from 12 stations across the PG and a variety of meteorological information, including satellite imagery, high-altitude isohypse maps and high-resolution air pressure records from 47 instruments along the PG. Our results show that the event was very local, with recorded maximum trough-to-crest wave heights of 197 cm at Dayyer and 234 cm at Asaluyeh, near field cities in Iran located * 80 km apart. The dominant wave periods were in the range of 15–20 min. At all distant tide gauges, the observed wave heights were \ 35 cm. No earthquakes or landslides were evident at the time of the event. On the other hand, atmospheric processes during 18–22 March were very active and 10 distinctive tsunamigenic air pressure disturbances were observed propagating over the PG, suggesting that the event of 19 March 2017 was a ‘‘meteorological tsunami’’. Atmospheric conditions over the PG were highly favourable for the generation of meteotsunamis and very similar to those that caused a chain of strong meteotsunamis in the Mediterranean and Black Sea regions during 23–27 June 2014. Based on the 500 hPa wind, we evaluated that the disturbances had propagation speeds of 21–38 m/s, with the disturbance at Dayyer having a speed of ~ 26 m/s toward 77º True. The Froude number, Fr (estimated as the ratio of the air disturbance speed to the long wave speed), on 19 March 2017 in the Dayyer/Asaluyeh region was close to resonance, Fr ~ 0.9 to 1.1, which is highly favourable for meteotsunami generation. Our findings indicate that the Dayyer/Asaluyeh area is a ‘‘hot spot’’ that is highly vulnerable to extreme, weather-induced tsunami-like waves. Brunel University London, Russian State Assignment, FCT, Croatian Science Foundation

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.

The paper presents the Adriatic Sea and Coast (AdriSC) Meteotsunami Forecast system, which has been developed to operationally forecast meteotsunamis – atmospherically-generated destructive ocean waves in the tsunami frequency band, in the Adriatic Sea. The challenges posed by modelling meteotsunamis are first reviewed, then the AdriSC Meteotsunami Forecast system set-up is presented in detail and finally the atmosphere and ocean model results are evaluated against 48 air pressure sensors and 19 tide gauges for six different meteotsunami events. The statistical analysis of the high-frequency model results reveals that the AdriSC atmospheric and ocean models can reproduce meteotsunami events, even though their performances highly vary depending on the event and observation location. A qualitative analysis of the maps of extreme sea level and mean sea level pressure high-frequency model results shows that even a slight shift in location (of the order of 1 to 10 km) of the atmospheric disturbances, responsible for the meteotsunami generation, results in the incapability of the ocean models to reproduce the observed floods occurring during the meteotsunami events. This study presents the first available thorough evaluation of a deterministic meteotsunami forecast system. As such, it establishes that a carefully envisioned modelling system, even if imperfect, can be implemented to reproduce and forecast meteotsunami events.

A series of meteotsunamis hit a few locations in the Mediterranean and Black Seas during 22– 27 June 2014. Meteot- sunamis were particularly numerous on 25 and 26 June in the Adriatic Sea, where at least six harbours and bays were stricken by ˇ powerful waves: strongest events occurred in Vela Luka (Korcula Island), a known meteotsunami hot-spot, where waves reached ˇ height of *3 m, and in Rijeka dubrovacka Bay, where strong *5 m/s currents accompanied *2.5 m high waves. Inten- sification 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 distur- bances 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 gen- erated 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 enhance- ment 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.

A climate synoptic meteotsunami index has been constructed using synoptic variables for the Balearic Islands. The index allows for the very first assessment of atmospherically driven intense sea level oscillations at the tsunami timescale (, Sí

A performance analysis of the NEMOMED8 ocean regional circulation model was undertaken for the Adriatic Sea during the period of 1961– 2012, focusing on two mechanisms, dense water formation (DWF) and the Adriatic–Ionian Bimodal Oscillating System (BiOS), which drive interannual and decadal variability in the basin. The model was verified based on sea surface temperature and sea surface height satellite measurements and long-term in situ observations from several key areas. The model qualitatively reproduces basin-scale processes: thermohaline-driven cyclonic circulation and freshwater surface outflow along the western Adriatic coast, dense water dynamics, and the inflow of Ionian and Levantine waters to the Adriatic. Positive temperature and salinity biases are reported ; the latter are particularly large along the eastern part of the basin, presumably because of the inappropriate introduction of eastern Adriatic rivers into the model. The highest warm temperature biases in the vertical direction were found in dense-water-collecting depressions in the Adriatic, indicating either an inappropriate quantification of DWF processes or temperature overestimation of modelled dense water. The decadal variability in the thermohaline properties is reproduced better than interannual variability, which is considerably underestimated. The DWF rates are qualitatively well reproduced by the model, being larger when preconditioned by higher basin-wide salinities. Anticyclonic circulation in the northern Ionian Sea was modelled only during the Eastern Mediterranean Transient. No other reversals of circulation that could be linked to BiOSdriven changes were modelled.

This paper contains a basin-wide assessment of high-frequency sea level oscillations in the Mediterranean Sea for the period from 2010 to 2014. Sea level series with temporal resolutions of 1 min were taken from 29 tide gauges that had been operational for at least 4 years with high-quality time series. The contribution of high-frequency sea level variance (2 min–6 h) to the total and residual sea level variance was estimated to vary between 0.4% and 9.5% and between 0.6% and 12.1%, respectively, but to become dominant at some stations during extreme high-frequency events. A total of 36 high-frequency sea level events were extracted from the series, with some occurring locally in one of the four selected regions of Spain, Sardinia, Sicily and the Greece–Ionian Sea (6 events), some occurring over two or three regions (19 events), and some occurring in all of the selected regions within a period of 1–3 days (11 events). The basin-wide events normally propagate from the western to the eastern parts of the basin, with an average velocity of approximately 30 km/h. Synoptic patterns associated with high-frequency events were analysed, and a high resemblance to patterns associated with meteotsunamis was observed: (i) a cyclone with a centre W-NW from the affected area, (ii) a strong thermal front in the lower troposphere, and (iii) a forefront of an unstable strong mid-tropospheric jet placed over the affected area. The strong coherence between high-frequency sea level events and synoptic patterns introduces the possibility of a timely forecast of these events.

We analyzed long-term time series of temperature, salinity, and dissolved oxygen (DO) concentrations collected along the Palagruža Sill transect (middle Adriatic) between 1952 and 2010. The data have been mostly collected on seasonal basis, allowing for extraction of seasonal signal from the series. By applying Self-Organizing Maps (SOM) method, a kind of unsupervised neural network method, the processes on a decadal time scale emerged as the most relevant for changes of oceanographic properties in the middle Adriatic area. Sensitivity studies revealed that oceanographic patterns obtained by SOM were not sensitive to shortening of time series, to removal of data from one station or to removal of DO from the analysis. Simultaneous SOM-based mapping of sea surface heights in the northern Ionian Sea, with these heights serving as a proxy for the Adriatic-Ionian Bimodal Oscillating System (BiOS), revealed asymmetry between anticyclonic and cyclonic BiOS patterns and correlated the decadal oscillations in the middle Adriatic with the reversals in the BiOS circulation regimes. These reversals are found to either rapidly change oceanographic properties in the middle Adriatic (e.g., during the Eastern Mediterranean Transient) or to change them with a time lag of 2–3 years. The mapped connections may be used for a short-time (a few years) forecasting of the Adriatic oceanographic properties or for mapping future climate decadal oscillations as seen by ocean climate models.

Present investigations of sea level extremes are based on hourly data measured at coastal tide gauges. The use of hourly data restricts existing global and regional analyses to periods larger than 2 h. However, a number of processes occur at minute timescales, of which the most ruinous are tsunamis. Meteotsunamis, hazardous nonseismic waves that occur at tsunami timescales over limited regions, may also locally dominate sea level extremes. Here, we show that nonseismic sea level oscillations at tsunami timescales (

The paper investigates wintertime dynamics of the coastal northeastern Adriatic Sea, and is based on numerical modelling and in situ data collected through field campaigns executed during the winter and spring of 2015. The data have been collected by a variety of instruments and platforms (ADCPs, CTDs, glider, profiling float), and have been accompanied with a one-way coupled ALADIN/ROMS modelling effort. Research focus has been put on dense water formation (DWF), thermal changes and circulation, and water exchange between the coastal and open Adriatic. According to both observations and modelling results, dense waters are formed in the northeastern coastal Adriatic during cold bora outbreaks, even during milder-than-average winters (as was the winter of 2015). However, dense water formed in this coastal region has, due to lower salinities, lower densities than dense water formed at the open Adriatic. Since the sea is deeper in the coastal area than at the open Adriatic, dense waters from the open Adriatic occasionally enter the coastal area near the bottom of the connecting passages, while the surface flow is mostly outward from the coastal area. Median residence time of the coastal area is estimated to about 1–2 months, indicating that the coastal area may be relatively quickly renewed by the open Adriatic waters. The model significantly underestimates currents and transports in connecting channels, which may be a result of a too coarse resolution of atmospheric forcing, misrepresentation of bathymetry or absence of the air-sea feedback in the model. Obtained data represents a comprehensive marine dataset, pointing to a number of interesting phenomena to be investigated in the future.

A systematic survey of high-frequency sea level oscillations (

In this paper, we document observational support for the long-term weakening of the northwestern part of the Adriatic-Ionian thermohaline cell (AITHC), one of the three cells that drive the deep Mediterranean thermohaline circulation. The AITHC weakening is detected from long-term temperature, salinity and dissolved oxygen trends estimated from data measured between 1952 and 2010 along the Palagruža Sill, Adriatic Sea. We assumed that the weakening of the AITHC may be deduced from long-term changes in the dense water outflow characteristics across the sill, which are characterized by a strong decrease in dissolved oxygen content, slight warming, and shallowing of the outflow and by lower advection of saline and warmer Levantine Intermediate Water (LIW) toward the northwestern Adriatic. The latter was deduced from the negative temperature trends and the lowest salinity trends estimated for the area of LIW inflow. Further weakening of the AITHC may have a noteworthy impact on deep aquatic systems and should therefore be monitored and assessed regularly.

A synoptic atmospheric index is constructed for the region of the Balearic Islands, Spain. The index links the occurrence of meteotsunamis, i.e., atmospherically induced high-frequency sea level oscillations (2 min

An ocean surface currents forecasting system, based on a Self-Organizing Maps (SOM) neural network algorithm, high-frequency (HF) ocean radar measurements and numerical weather prediction (NWP) products, has been developed for a coastal area of the northern Adriatic and compared with operational ROMS-derived surface currents. The two systems differ significantly in architecture and algorithms, being based on either unsupervised learning techniques or ocean physics. To compare performance of the two methods, their forecasting skills were tested on independent datasets. The SOM-based forecasting system has a slightly better forecasting skill, especially during strong wind conditions, with potential for further improvement when data sets of higher quality and longer duration are used for training.

The understanding of meteotsunamis - significant atmospherically generated long ocean waves in the tsunami frequency band - has advanced considerably during the last two decades. Scientists and specialists use near-field in situ data and remote observations, as well as atmospheric and ocean modelling, to study destructive events. The phenomenon has been reported and investigated worldwide, indicating its relevance within other marine natural hazards and demonstrating the urgent need for meteotsunami warning systems for certain countries. In this paper we summarize the present knowledge of the phenomenon, identify particular research gaps, and propose near-future critical components of meteotsunami research. We emphasize a potential concept of merging yet-to-be-developed meteotsunami warning systems and existing tsunami or multi-hazard early warning systems.

This study aims to document the effects of imposing different river runoff forcing and tidal forcing to the dense water formation (DWF) rates and dynamics in a semi-enclosed sea. An extreme DWF episode that occurred in the winter of 2012 in the shallow northern Adriatic Sea during a prolonged cold bora wind outbreak event has been reproduced using a one-way coupled atmosphere-ocean modelling system comprised of the atmospheric Aladin/HR mesoscale model and ocean ROMS model. Three different river runoff forcing and tides/no tides scenarios were imposed on the model. The introduction of tides and river climatology instead of real rivers did not substantially change the modelled DWF transports and volumes, whereas the simulation using the old Raicich climatology resulted in a substantial freshening of the entire Adriatic that reduced or prevented the DWF at sites in the northern and northeastern Adriatic. The necessity of using an up-to-date river runoff climatology to properly reproduce the DWF in semi-enclosed seas is emphasised.

The goal of the paper is to investigate environmental influences on the occurrence of anchovy spawning over a year, in order to enable the timing and strength of high spawning activity to be predicted. Biological sampling of anchovy was conducted on the fishing ground of the eastern Adriatic (the northernmost semi-enclosed basin in the Mediterranean) on a monthly basis from January 1999 to December 2010, while data on environmental parameters were taken from in situ measurements at the most representative and best surveyed eastern Adriatic hydrographic station and from I-COADS monthly surface climatological fields. Anchovy spawning seasonality was defined by monthly changes of the maturity stages and the gonadosomatic index. Fluctuations of the gonadosomatic index reveal that spawning begins in March and lasts till September, with reproductive activity peaking from April to July. Early or late occurrence of a high gonadosomatic index has a significant negative correlation with upper layer salinity in the two preceding months and a sporadic and weak connection with the wind-mixing index and surface temperature. An enhanced input of nutrient-rich freshwater of river origin, which reduces upper layer salinity and enhances primary production up to two months before anchovy spawning, seems to be important for the anchovy fertility, especially if a late spawning maximum (in July) occurs in a certain year.

Long-term time series of physical and chemical parameters collected between 1960 and 2010 along the Palagruža Sill transect, Middle Adriatic Sea, have been investigated in terms of average water properties and their variability. Nutrients, especially orthophosphates, reached rather high levels of concentration below the euphotic zone between 1991 and 1998, the highest levels in the investigated period. Simultaneously, the N:P ratio, which is normally higher than 25:1, decreased to values less than 16:1 in the euphotic zone, indicating a switch from typical phosphorus to nitrogen- limited preconditioning for the primary production. Higher-than-usual nutrient levels peaking in the mid-1990s, coupled with lower-than-usual temperature, salinity, dissolved oxygen and pH values, are presumably related to the flow of the nutrient richer Western Mediterranean waters to the Adriatic below the euphotic layer. These waters, which keep their footprint in the N:P ratio, enter the Adriatic during the anticyclonic phase of the Bimodal Adriatic-Ionian Oscillation (BiOS), which has been uniquely strengthened by the Eastern Mediterranean Transient occurring in the early 1990s. This hypothesis should be confirmed through targeted research and modelling exercises, as it is highly relevant for the biogeochemistry of the Adriatic Sea.

Global long-term sea-level variability trends and regional coherence patterns were mapped based on hourly sea-level time series data from the 29 longest operating tide gauge stations distributed worldwide. We split sea-level variability into three frequency bands: (1) small-scale synoptic bands (1–3 d), (2) large-scale synoptic bands (3–10 d) and (3) planetary-scale bands (10–100 d). We then calculated seasonal and annual trends. The most coherent result obtained involved a significant decrease in sea-level variability over the tropical and subtropical Pacific, particularly at the synoptic scale frequencies. Several other coherent regions were found and linked to changes in the global atmosphere. Copyright © 2012 Royal Meteorological Society

The paper attempts to document long-term changes in deep Adriatic water patterns by applying the Self-Organising Maps (SOM) method to temperature, salinity, dissolved-oxygen content, orthophosphate and total inorganic nitrogen profiles sampled at a single deep station in the South Adriatic Pit (SAP) over a half century (1957–2009). Seasonality observed in upper layers has been removed by the least-squares fitting of the annual and semi-annual sinusoidal functions. The sensitivity of the SOM to various parameter combinations reveals the importance of temperature, salinity and dissolved oxygen for mapping different water patterns, while nutrients have less influence on quality and applicability of SOM solutions to the extraction of characteristic SAP water profiles. The quality of fit obtained for different combination of the measured parameters introduced to a SOM suggests that the incomplete combinations of input parameters increase an imperfection in the applicability of SOMs to the dataset. Two modes of long-term changes in the SAP obtained by the SOM analyses are discussed with respect to the processes that drive the variability in the area, e.g., the Adriatic-Ionian Bimodal Oscillation: where the first mode is characterised by rapid changes in the transition of SAP water masses, observed before 1980s (less adoptable by the SOMs), and the second mode is characterised by steady transitions (better adoptable by the SOMs), observed in the 1990s and the 2000s. The SOM method is found to have certain advantages when compared to other methods that have previously been used to distinguish the Adriatic water masses, as it does not depend on predefinition of water mass sources and allows for gaps in series.

The Adriatic Sea meteotsunami research and warning network is described. The network is located in the middle Adriatic, an area where the most destructive of the Adriatic meteotsunamis (destructive tsunami-like sea level oscillations generated by air pressure oscillations) occur. The network consists of three microbarograph meteorological stations, and is supplemented by four permanent tide-gauge stations. The two strongest air pressure disturbances, detected in almost a year and a half of measurements, are examined in more detail and used to test functionality and applicability of the network. Both of these disturbances had a meteotsunami favourable velocity, however, only one generated a meteotsunami. It is discussed why this happened and additional information on creating a meteotsunami warning system are obtained. Methods to construct a simple low-cost meteotsunami warning network are given.

This paper documents the variability and trends of mean storminess and extreme sea level amplitudes at selected long-term operating tide gauge stations located in the European Seas over different frequency bands, seasons and months. Six stations have been chosen for the analyses–Antalya, Ceuta, Rovinj, Newlyn, Wladyslawowo and Lerwick–which possess at least a half-centurial record of hourly or higher frequency sea level data. The data have been carefully inspected for time shifts and drifts in the record. The analyses included the extraction of sea level amplitudes (envelopes) over four frequency bands: super-diurnal frequencies (0–1 days), small-scale synoptic disturbances (1–3 days), large-scale synoptic disturbances (3–10 days) and planetary-scale disturbances (10–100 days). Interannual variability in sea level amplitudes is occasionally found to coincide with some known variability in the atmosphere. For example, the northern European stations have overall positive sea level storminess and extreme trends, which is opposite from the southern stations, confirming a northward shift in atmosphere storm tracks. Redistribution of sea level amplitudes between different seasons and different frequency bands has been observed at some stations in both variability and trends. The latter may be important for the assessment of a region's total hazard risks and vulnerability, as maximum storminess and extremes may or may not coincide with maximum mean sea level.

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.

A series of tsunami-like waves of non-seismic origin struck several southern European countries during the period of 23 to 27 June 2014. The event caused considerable damage from Spain to Ukraine. Here, we show that these waves were long-period ocean oscillations known as meteorological tsunamis which are generated by intense small-scale air pressure disturbances. An unique atmospheric synoptic pattern was tracked propagating eastward over the Mediterranean and the Black seas in synchrony with onset times of observed tsunami waves. This pattern favoured generation and propagation of atmospheric gravity waves that induced pronounced tsunami-like waves through the Proudman resonance mechanism. This is the first documented case of a chain of destructive meteorological tsunamis occurring over a distance of thousands of kilometres. Our findings further demonstrate that these events represent potentially dangerous regional phenomena and should be included in tsunami warning systems.