Analysis of the eastern Adriatic sea level extremes

Aim: To examine the frequency, strength, and driving mechanisms of the eastern Adriatic sea level extremes. Methods: In 2017, a tide-gauge station, and a meteorological station have been installed at Stari Grad (Hvar Island, eastern middle Adriatic Sea). Three years of sea level and atmospheric measurements were analysed. Ten strongest episodes of the following extreme types were extracted from sea level data: positive long-period (T >210 min) extremes; negative long-period (T >210 min) extremes; short-period (T < 210) extremes. Long-period extremes were defined as situations when sea level surpasses (is lower than) 99.7 (i.e., 2) percentile of residual long-period sea level height, and short-period extremes as situations when 2.5-h variance of short-period sea level oscillations is higher than 99.4 percentile of total variance of short-period series. Types of sea level extremes were subsequently associated to characteristic atmospheric situations. Results: Positive long-period extremes commonly appeared during the presence of low-pressure atmospheric systems over the Adriatic – such system were accompanied with strong SE winds. Negative long-period extremes were associated with presence of high atmospheric pressure fields over the Adriatic Sea, either with strong NE winds, or calm weather. Appearance of short-period sea level extremes corresponded to either low atmospheric pressure fields and strong SE wind, or normal/high pressure fields and calm weather/no winds over the Adriatic. A strong seasonal signal was detected, with the positive long-period extremes occurring mostly during November to February, and the negative long-period extremes occurring during January to February. The short-period extremes appeared throughout the year, but strongest events appeared during May to July. Conclusion: Results show that Stari Grad is a flood-prone location, both when it comes to positive long-period extremes and to short-period extremes. Furthermore, long-period and short-period extremes occasionally occur simultaneously in Stari Grad, pointing to a previously unknown added hazard level

Seši Bakarskog zaljeva i njihova povezanost s atmosferskim procesima

Large-amplitude seiches (up to 40 cm) were recorded at a tide-gauge inside Bakar Bay from 19–21 August 2006. They were analysed using available tide-gauge and meteorological (air pressure and wind, vertical sounding) data. Sea level and air pressure spectra showed simultaneous increases of energy in the periods in which the seiches of both Bakar Bay (about 20 min) and Rijeka Bay (ca. 2 h) occurred. The propagation speed and direction as well as the horizontal span of the four pronounced pressure disturbances, favourable for coupling with Rijeka Bay waters via the Proudman resonance, were determined. It is argued that only short atmospheric pressure disturbances may generate significant barotropic sea waves in a small basin such as Rijeka Bay; once generated they are amplified when hitting Bakar Bay due to the harbour resonance. Furthermore, examination of the synoptic situation and upper-air soundings revealed the presence of dynamically unstable layer at a height of around 2000 m which was also the height of temperature inversion that developed as a consequence of an advection of warm African air from the south-east. During the afternoon hours of 19 August 2006 wind speed in this layer was close to the estimated speed of propagation of the air pressure disturbances which, together with dynamical instability, made conditions favourable for long distance propagation and trapping of atmospheric gravity waves.Seši iznimne amplitude (do 40 cm) zabilježeni su u nekoliko navrata na mareografskoj postaji u Bakarskom zaljevu između 19. i 21. kolovoza 2006. Analizirani su dostupni mareografski (razina mora) i meteorološki (tlak zraka, brzina i smjer vjetra, radio-sondažna mjerenja) podaci. Spektralna analiza vremenskih nizova razine mora i tlaka zraka ukazala je na istovremeni porast energije na periodima koji uključuju periode seša Bakarskog (oko 20 min) i Riječkog zaljeva (oko 2 h). Izračunati su brzina i smjer rasprostiranja te horizontalna širina četiri poremećaja u polju tlaka zraka koji su Proudmanovom rezonancom mogli djelovati na Riječki zaljev. Konačno, zaključeno je da su samo kratki poremećaji u polju tlaka zraka mogli generirati značajne barotropne valove u zaljevu ograničenih dimenzija kakav je Riječki zaljev, te da su se ti valovi dodatno pojačali u Bakarskom zaljevu mehanizmom lučke rezonance. Uz to, analiza sinoptičke situacije i radio-sondažnih mjerenja ukazala je da su na visini od oko 2000 m postojali dinamički nestabilan sloj te temperaturna inverzija koja se razvila zbog advekcije toplog afričkog zraka. Tijekom popodnevnih sati 19. kolovoza brzina vjetra u ovom sloju je bila bliska izračunatoj brzini rasprostiranja poremećaja u polju tlaka zraka. Ovakvo podudaranje brzina uz postojanje dinamički nestabilnog sloja pogoduje dugotrajnom rasprostiranju i zarobljavanju atmosferskih težinskih valova

Stochastic Surrogate Model for Meteotsunami Early Warning System in the Eastern Adriatic Sea

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 stateâ ofâ theâ 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 seaâ level hazard forecast at endangered locations is then derived with an innovative stochastic surrogate modelâ implemented with generalized polynomial chaos expansion (gPCE) method and synthetic IGWs forcing a barotropic ocean modelâ 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 gPCEâ based methods can be used for atmospherically driven extreme seaâ level hazard assessment and in geosciences in wide.Plain Language SummaryAtmospherically driven extreme seaâ level events are one of the major threats to people and assets in the coastal regions. Assessing the hazard associated with such events together with uncertainty quantification in a precise and timely manner is thus of primary importance in modern societies. In this study, an early warning system for the eastern Adriatic meteotsunamis, destructive long waves with periods from few minutes up to an hour generated by traveling atmospheric disturbances, is presented and evaluated. The system is based on stateâ ofâ theâ art deterministic atmospheric and ocean models as well as an innovative statistical model developed to forecast the meteotsunami hazard. The evaluation reveals that the meteotsunami hazard is conservatively assessed but often overestimated. This study demonstrates that the presented methodology can be used for extreme seaâ level hazard assessment and in general for hazard studies in geosciences.Key PointsDesign and evaluation of an innovative meteotsunami early warning system prototype using stochastic surrogate approachForecast of the atmospheric internal gravity waves driving meteotsunami events with deterministic stateâ ofâ theâ art modelsStochastic surrogate model based on generalized polynomial chaos expansion methods and running at nearly no computational costPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152998/1/jgrc23744.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152998/2/jgrc23744_am.pd

Mediteranski meteotsunamiji iz svibnja 2021. i lipnja 2022. godine: Opažanja, analiza podataka i sinoptička pozadina

Meteorological tsunamis (i.e., tsunami-like waves of atmospheric origin) are regularly observed in the Mediterranean Sea. During a single event, destructive flooding usually occurs in one location or limited area. However, in May 2021 and June 2022, strong meteotsunamis hit several Mediterranean locations up to 500 km apart. In the morning hours of the 24th of May 2021, a meteotsunami hit Bonifacio on the island of Corsica (western Mediterranean, France) and in the afternoon hours of the same day, another meteotsunami hit Široka Bay on the island of Ist (Adriatic Sea, Croatia), 500 km away. About 13 months later, on the 26th of June 2022, a meteotsunami hit Ciutadella on the island of Menorca (Spain) and two days later Bonifacio, 400 km away. Sea-level and atmospheric pressure data and satellite imagery, as well as synoptic conditions, associated with both events were analysed in detail. It has been confirmed that in the Mediterranean, meteotsunamis occur when meteotsunamigenic synoptic conditions prevail over the area, with a strong southwesterly jet stream embedded in dynamically or convectively unstable atmospheric layers standing out as the most important condition. The meteotsunamigenic potential of each of the three bays (Ciutadella, Bonifacio, Široka Bay) was investigated by considering: (1) the potential for Proudman resonance on the shelves offshore of the bays, (2) the orientation of the mouth of the bay and (3) the frequency of meteotsunamigenic synoptic conditions over the area. The strongest and most frequent meteotsunamis occur at locations where the shelf characteristics (width, depth, orientation), bay mouth orientation and climatology of 500-hPa winds and atmospheric stability have characteristics that support the amplification of long-ocean waves and their propagation toward the bay mouth.U Sredozemnom moru redovito se opažaju meteotsunamiji, tj. tsunamiji meteorološkog podrijetla. Tijekom pojedinačnih događaja, destruktivni valovi koji izazivaju poplavljivanje obično se javljaju na samo jednoj lokaciji ili ograničenom području. Međutim, u svibnju 2021. i lipnju 2022. snažni meteotsunamiji pogodili su nekoliko lokacija na Mediteranu, međusobno udaljenih do 500 km. Tijekom jutarnjih sati 24. svibnja 2021. meteotsunami je pogodio Bonifacio na otoku Korzici (zapadni Mediteran, Francuska), dok je poslijepodne istog dana drugi meteotsunami pogodio oko 500 km udaljeni zaljev Široka na otoku Istu (Jadransko more, Hrvatska). Otprilike 13 mjeseci kasnije, 26. lipnja 2022., meteotsunami je pogodio Ciutadellu na otoku Menorca (Španjolska) te dva dana kasnije 400 km udaljeni Bonifacio na Korzici. Detaljno su analizirana mjerenja razine mora i tlaka zraka, satelitske snimke te sinoptički uvjeti tijekom oba događaja. Potvrđeno je da se mediteranski meteorološki tsunamiji javljaju za vrijeme povoljnih sinoptičkih uvjeta – snažna jugozapadna mlazna struja unutar dinamičkih ili konvektivno nestabilnih atmosferskih slojeva prepoznata je kao najvažniji uvjet. Potencijal za nastanak meteotsunamija određen je za sva tri zaljeva (Ciutadella, Bonifacio, Široka) na temelju: (1) procjene potencijala za Proudmanovu rezonanciju na morskim pojasevima ispred zaljeva, (2) orijentacije ulaza u zaljev i (3) učestalosti sinoptičkih uvjeta povoljnih za nastanak meteoroloških tsunamija. Najjači i najučestaliji meteorološki tsunamiji javljaju se na lokacijama na kojima karakteristike morskog pojasa (širina, dubina, orijentacija), orijentacija ulaza u zaljev i distribucija povoljnih sinoptičkih uvjeta, imaju karakteristike koje pogoduju amplifikaci-ji dugih valova otvorenog mora te njihovom širenju prema zaljevu

Mediteranski meteotsunamiji iz svibnja 2021. i lipnja 2022. godine: Opažanja, analiza podataka i sinoptička pozadina

Meteorological tsunamis (i.e., tsunami-like waves of atmospheric origin) are regularly observed in the Mediterranean Sea. During a single event, destructive flooding usually occurs in one location or limited area. However, in May 2021 and June 2022, strong meteotsunamis hit several Mediterranean locations up to 500 km apart. In the morning hours of the 24th of May 2021, a meteotsunami hit Bonifacio on the island of Corsica (western Mediterranean, France) and in the afternoon hours of the same day, another meteotsunami hit Široka Bay on the island of Ist (Adriatic Sea, Croatia), 500 km away. About 13 months later, on the 26th of June 2022, a meteotsunami hit Ciutadella on the island of Menorca (Spain) and two days later Bonifacio, 400 km away. Sea-level and atmospheric pressure data and satellite imagery, as well as synoptic conditions, associated with both events were analysed in detail. It has been confirmed that in the Mediterranean, meteotsunamis occur when meteotsunamigenic synoptic conditions prevail over the area, with a strong southwesterly jet stream embedded in dynamically or convectively unstable atmospheric layers standing out as the most important condition. The meteotsunamigenic potential of each of the three bays (Ciutadella, Bonifacio, Široka Bay) was investigated by considering: (1) the potential for Proudman resonance on the shelves offshore of the bays, (2) the orientation of the mouth of the bay and (3) the frequency of meteotsunamigenic synoptic conditions over the area. The strongest and most frequent meteotsunamis occur at locations where the shelf characteristics (width, depth, orientation), bay mouth orientation and climatology of 500-hPa winds and atmospheric stability have characteristics that support the amplification of long-ocean waves and their propagation toward the bay mouth.U Sredozemnom moru redovito se opažaju meteotsunamiji, tj. tsunamiji meteorološkog podrijetla. Tijekom pojedinačnih događaja, destruktivni valovi koji izazivaju poplavljivanje obično se javljaju na samo jednoj lokaciji ili ograničenom području. Međutim, u svibnju 2021. i lipnju 2022. snažni meteotsunamiji pogodili su nekoliko lokacija na Mediteranu, međusobno udaljenih do 500 km. Tijekom jutarnjih sati 24. svibnja 2021. meteotsunami je pogodio Bonifacio na otoku Korzici (zapadni Mediteran, Francuska), dok je poslijepodne istog dana drugi meteotsunami pogodio oko 500 km udaljeni zaljev Široka na otoku Istu (Jadransko more, Hrvatska). Otprilike 13 mjeseci kasnije, 26. lipnja 2022., meteotsunami je pogodio Ciutadellu na otoku Menorca (Španjolska) te dva dana kasnije 400 km udaljeni Bonifacio na Korzici. Detaljno su analizirana mjerenja razine mora i tlaka zraka, satelitske snimke te sinoptički uvjeti tijekom oba događaja. Potvrđeno je da se mediteranski meteorološki tsunamiji javljaju za vrijeme povoljnih sinoptičkih uvjeta – snažna jugozapadna mlazna struja unutar dinamičkih ili konvektivno nestabilnih atmosferskih slojeva prepoznata je kao najvažniji uvjet. Potencijal za nastanak meteotsunamija određen je za sva tri zaljeva (Ciutadella, Bonifacio, Široka) na temelju: (1) procjene potencijala za Proudmanovu rezonanciju na morskim pojasevima ispred zaljeva, (2) orijentacije ulaza u zaljev i (3) učestalosti sinoptičkih uvjeta povoljnih za nastanak meteoroloških tsunamija. Najjači i najučestaliji meteorološki tsunamiji javljaju se na lokacijama na kojima karakteristike morskog pojasa (širina, dubina, orijentacija), orijentacija ulaza u zaljev i distribucija povoljnih sinoptičkih uvjeta, imaju karakteristike koje pogoduju amplifikaci-ji dugih valova otvorenog mora te njihovom širenju prema zaljevu

Coastal Sea Level Monitoring in the Mediterranean and Black Seas

Spanning over a century, a traditional way to monitor sea level variability by tide gauges is – in combination with modern observational techniques like satellite altimetry – 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 last decades allowed for extending the applications towards a variety of users and coastal hazard managers. The Mediterranean and Black50 seas are an example for such a transition – while having a long tradition for sea level observations with several records spanning over a century, the number of modern tide gauge stations are 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 description of major monitoring networks in the Mediterranean and Black55 seas and their characteristics, including the type of sea level sensors, measuring resolutions, data availability and existence of ancillary measurements, altogether collecting information about 236 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 at different repositories. Finally, an assessment of the networks’ capabilities60 for their usage in different sea level applications has been done, with recommendations that might mitigate the bottlenecks and assure further development of the networks in a coordinated way, being that more necessary in the era of the human-induced climate changes and the sea level ris