The wind climatology of the Adriatic Sea deduced from coastal stations

Summary We have tested the model developed within the EU ?European Wind Atlas? project under particularly critical conditions of thermal non-neutrality, and with simulations at distances exceeding 100 km. For this purpose we have used six coastal stations of the Adriatic Sea and one located 16 km off the coast of Venice. The performances and the limits of the model rise out by comparing the experimental results with the simulations. Then we have estimated the probability density functions of the wind speed in the Adriatic Sea for different heights above sea level, Finally, we have attempted an interpolation of these functions along the Adriatic Sea, from Venice to Brindisi.     

Solitary waves in the gulf of quarnaro revealed by LANDSAT thematic mapper

Summary The propagation of solitary wave trains in the Adriatic Sea is studied by means of LANDSAT Thematic-Mapper images. The baroclinic Rossby radius of deformation has been estimated from the width of a baroclinic current observed along the coast of Croatia using AVHRR data. The phase speed of the linear internal waves has been consequently estimated and the compatibility of the Kortweg-de Vries equations with experimental data has been tested. Satellite-derived wave parameters are in good agreement with a plane-bottom, shallow-water solitary-wave model.     

Wind evaluation in the Adriatic sea

Summary A severe storm in the Adriatic Sea has been hindcast with two meteorological models, respectively at the local (LAMBO) and global scale (T213). We have found that the increase of resolution is not paralleled by a corresponding increase of the overall accuracy. This is particularly true when the wind fields are used to evaluate the corresponding wave fields. The LAMBO data have then been used to validate a simpler wind model that, when properly tuned to the specific basin and starting from the correct pressure fields, is capable to supply surface wind fields of acceptable quality. Deceased in November 1995.     

Fluctuation analysis of meteo-marine data

We study long-term behaviour of air temperature, wave heights and wind speed time series recorded for the period 1993–1997 at a meteo-marine station located in the Adriatic Sea. The scaling analysis shows that fluctuations of air temperature display long-range autocorrelations, while those for wave heights show a more complex behaviour, crossing over from a persistent regime at intermediate time scales (up to about 20 days) to an anti-persistence behaviour at longer times. Furthermore, the crosscorrelations of their records are found to be large, with a covariance of about -0.3 (indicating anti-crosscorrelations) within the full 5-years period, giving a quantitative measure of the actual coupling between the two data sets. Wind speed fluctuations are found to be strongly crosscorrelated (about 0.6) with those of wave heights, indicating as expected that wind is the main driving force for wave height fluctuations.     

Noise-driven intermittency in tidal dynamics

Summary The tide nonstationarity in the Adriatic Sea is described. We show how this phenomenon can be related to the stochasticity of sea fetch by a nonlinear noise-forced oscillator model. The experimental series correlation dimension reveals a strong lifting with respect to the astronomic tide. The lifting is related to space-time intermittency.     

Resistance to stress and Hc functional modulation in Liocarcinus sp

This study is included in a project aimed to study the alterations on the structure of the Northern Adriatic Sea ecosystem produced by fishing activity. The indirect or secondary effects of fishery such as the changes of the structure and trophic relationships of the ecosystem are under investigation and we have particularly considered the effects on species such as Liocarcinus depurator that are captured and then rejected because devoid of commercial value. The objective of this study is the Liocarcinus sp. adaptative resistance to stress and the effects of biochemical parameters (allosteric effectors) on Hc functional modulation.     

Remarks on a pronounced meteomarine event in the Northern Adriatic Sea in spring 1992

Summary This note is an updating of a previous paper by the same authors, where, by means of a semi-empirical analytical model, a whole correlation was found between the recent appearance of broad algal-bloom events up to 1991 and pronounced advection episodes in the Northern Adriatic Sea. The investigation of some features of the event in spring 1992 has induced us to refine the model in order to extent consistently the correlation above.     

Waves in front of the Venetian littoral

Summary The second-generation HISWA model, specifically developed for shallow water areas, was used to estimate the wave conditions in front of the Venetian littoral. The model is based on the wave action equation, and it includes conservative interactions with bottom and currents, generation by wind and dissipation by bottom friction and breaking. A detailed sensitivity analysis has been carried out on the main processes that affect the output of the model. The performance of the model has then been checked by comparison with laboratory and field data. Finally, the HISWA model has been applied to several severe storms which have occurred in the Northern Adriatic and also to extreme wave conditions in the same area, thus allowing the corresponding wave conditions at the coast to be estimated. The results suggest that wave evolution towards the coast is greatly influenced by bottom friction in intermediate water depth and by breaking in shallow water. These processes could lead to saturation conditions during extreme wave events.     

A semi-empirical model of tracer advection in the Northern Adriatic Sea

Summary The advection of a hypothetical conserved tracer in the Northern Adriatic Sea is studied by means of a semi-empirical model employing observed meteomarine parameters, during the first four months of the year, from 1986 to 1991. Pronounced advection episodes are singled out simply on magnitude order arguments; they turn out to be clearly correlated with the appearance of the algal bloom events of 1988, 1989 and 1991 and suggest a climatological arrangement of this phenomenon.     

Nonlinear shoaling of shallow water waves: perspective in terms of the inverse scattering transform

Summary We study nonlinear interactions in measured surface wave trains obtained in the Northern Adriatic Sea about 16 kilometres from Venice, Italy.Nonlinear Fourier analysis is discussed in terms of the exact spectral solution to the Korteweg-deVries (KdV) equation as given by theinverse scattering transform (IST). For the periodic and/or quasi-periodic boundary conditions assumed herein, the approach may be viewed as a nonlinear, broad-banded generalization of the ordinary, linear Fourier transform. In particular, we study solition interactions, their properties and the nonlinear dynamics of the radiation (or oscillation) modes as found from the inverse scattering transform analysis. We also conduct a number of computer experiments in which measured wave trains are numerically propagated forward in time toward shallow water and backward in time into deep water in order to assess how the nonlinear wave dynamics are influenced by propagation over variable bathymetry. On this basis we develop a scenario for the evolution of nonlinear wave trains, initially far offshore in deep water, as they propagate into shallow water regions. The deep-water waves have a small Ursell number and are hence not very nonlinear; as they propagate toward shallow water, the Ursell number gradually increases in the numerical experiments by about an order of magnitude. A useful parameterization of nonlinearity in these studies is the ?spectral modulus,? a number between 0 and 1, which is associated with each IST spectral frequency. Small values of the modulus mean that a particular spectral component is linear (a sine wave); large values of the modulus (≈1) indicate that the component is nonlinear (a soliton). There is a systematic increase of the modulus as the waves propagate into shallow water where nonlinear effects predominate; we describe how the modulus varies as a function of spectral frequency during this shoaling process. The results suggest that the effect of increasing nonlinearity ?saturates? the IST spectrum (i.e. the modulus ≈1 for all frequencies) to that virtually all spectral components become solitons in sufficiently shallow water.     

Effects of fish farm loading on sea grass Posidonia oceanica at Vrgada Island (Central Adriatic): a nitrogen stable isotope study

Analyses of nitrogen stable isotopes in the marine sea grass Posidonia oceanica were used to investigate the influence of fish farming on the coastal ecosystem of Vrgada Island in the Murter Sea, Central Adriatic. The results show a statistically significant 15N enrichment (up to 4.7 per thousand at p < 0.005) in P. oceanica leaf and shoot tissues from fish cage sites with respect to the unaffected offshore reference site of Lumbarda Reef Flat (Kornati Islands). Heavy nitrogen enrichment was also detected in other benthic organisms analysed during this study and is attributed to the absorption and assimilation of 15N-enriched fish farm derived nitrogen waste.     

Mytilus galloprovincialis as a bioindicator of environmental conditions: the case of the eastern coast of the Adriatic Sea

The marine mussel Mytilus galloprovincialis lives attached to the surface of hard substrata, where its exposure and relative immobility allow it to record changes in ambient seawater. It is also found along the eastern coast of the Adriatic Sea. Oxygen and carbon isotopes were analysed for calcite and aragonite in separate shell layers, while major, minor and trace elements in the bulk shell were analysed to evaluate environmental conditions such as the temperature of carbonate deposition, freshwater influence and locations of anthropogenic pollution. We found that, on average, aragonite is enriched by 1.1‰ in (13)C and by 0.2‰ in (18)O compared with calcite. The calculated temperatures for M. galloprovincialis shell growth from the investigated area range from 13.4 to 20.9 °C for calcite and from 16.6 to 23.1 °C for aragonite. According to the δ(18)O and δ(13)C values of shell layers, we can separate the investigated area into three locations: those with more influence of freshwater, those with less influence of freshwater and those with marine environments. The highest concentrations of manganese, barium, boron, arsenic, nickel and chromium were observed in shells from Omis, Bacvice and Zablace (Central Adriatic) and Sv. Ivan (South Adriatic), where chemical and heavy industries are located and where sewage is known to be discharged into coastal areas. The highest concentrations of zinc, lead and copper were measured in samples from Pula, Rijeka and Gruz, where there are also ports in addition to industry.     

Sea surface temperature from AVHRR-2 data

Summary From the measurements in two channels of the 10 to 13 μm window region, the correction for the atmospheric absorption, useful to retrieve the sea surface temperature from satellite data, can be obtained. By using radiative-transfer model simulations, an up-to-date algorithm was developed, to retrieve the sea surface temperature from the AVHRR (advanced very high resolution radiometer) data. This algorithm has been compared with the algorithms found in the literature. A map of surface temperature in the Northern Adriatic Sea has been processed as an example of application of the algorithm developed. Visiting Scientist at the Joint Research Centre, Commission of the European Communities, 21020 ISPRA.     

Mytilus galloprovincialis as a bioindicator of environmental conditions: the case of the eastern coast of the Adriatic Sea

The marine mussel Mytilus galloprovincialis lives attached to the surface of hard substrata, where its exposure and relative immobility allow it to record changes in ambient seawater. It is also found along the eastern coast of the Adriatic Sea. Oxygen and carbon isotopes were analysed for calcite and aragonite in separate shell layers, while major, minor and trace elements in the bulk shell were analysed to evaluate environmental conditions such as the temperature of carbonate deposition, freshwater influence and locations of anthropogenic pollution. We found that, on average, aragonite is enriched by 1.1‰ in ¹³C and by 0.2‰ in ¹⁸O compared with calcite. The calculated temperatures for M. galloprovincialis shell growth from the investigated area range from 13.4 to 20.9 °C for calcite and from 16.6 to 23.1 °C for aragonite. According to the δ¹⁸O and δ¹³C values of shell layers, we can separate the investigated area into three locations: those with more influence of freshwater, those with less influence of freshwater and those with marine environments. The highest concentrations of manganese, barium, boron, arsenic, nickel and chromium were observed in shells from Omi?, Ba?vice and Zabla?e (Central Adriatic) and Sv. Ivan (South Adriatic), where chemical and heavy industries are located and where sewage is known to be discharged into coastal areas. The highest concentrations of zinc, lead and copper were measured in samples from Pula, Rijeka and Gru?, where there are also ports in addition to industry.     

Air-borne sound generated by sea waves

This paper describes a semi-empiric model and measurements of air-borne sound generated by breaking sea waves. Measurements have been performed at the Baltic Sea. Shores with different slopes and sediment types have been investigated. Results showed that the sound pressure level increased from 60 dB at 0.4 m wave height to 78 dB at 2.0 m wave height. The 1/3 octave spectrum was dependent on the surf type. A scaling model based on the dissipated wave power and a surf similarity parameter is proposed and compared to measurements. The predictions show satisfactory agreement to the measurements.     

Effects of fish farm loading on sea grass Posidonia oceanica at Vrgada Island (Central Adriatic): a nitrogen stable isotope study

Analyses of nitrogen stable isotopes in the marine sea grass Posidonia oceanica were used to investigate the influence of fish farming on the coastal ecosystem of Vrgada Island in the Murter Sea, Central Adriatic. The results show a statistically significant ¹⁵N enrichment (up to 4.7‰ at p?<?0.005) in P. oceanica leaf and shoot tissues from fish cage sites with respect to the unaffected offshore reference site of Lumbarda Reef Flat (Kornati Islands). Heavy nitrogen enrichment was also detected in other benthic organisms analysed during this study and is attributed to the absorption and assimilation of ¹⁵N-enriched fish farm derived nitrogen waste.     

Calibration with experimental data of a 2D sea breeze model by heating parametrization

Summary A new scheme of vertical distribution of sensible heat flux has been introduced in a bidimensional numerical sea breeze model which uses a prescribed flux at the ground. The scheme has been suggested by inspection of thermal and dynamical fields observed during a case study along the coast of northern Adriatic Sea. Agreement with data is shown to be considerably increased.

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Riassunto Un nuovo schema per la distribuzione verticale del flusso di calore sensibile è stato introdotto in un modello bidimensionale di brezza di mare in cui l’input termico è dato dal valore al suolo del flusso stesso. Lo schema è stato suggerito dall’analisi dei campi termici e dinamici osservati durante un ?case study? nel comprensorio Alto Adriatico, ed ha contribuito a migliorare sensibilmente i risultati della simulazione.

     

Box modeling of the Eastern Mediterranean sea

In ∼1990 a new source of deep water formation in the Eastern Mediterranean was found in the southern part of the Aegean sea. Till then, the only source of deep water formation in the Eastern Mediterranean was in the Adriatic sea; the rate of the deep water formation of the new Aegean source is 1 Sv, three times larger than the Adriatic source. We develop a simple three-box model to study the stability of the thermohaline circulation of the Eastern Mediterranean sea. The three boxes represent the Adriatic sea, Aegean sea, and the Ionian seas. The boxes exchange heat and salinity and may be described by a set of nonlinear differential equations. We analyze these equations and find that the system may have one, two, or four stable flux states. We conjecture that the change in the deep water formation in the Eastern Mediterranean sea is attributed to a switch between the different states on the thermohaline circulation; this switch may result from decreased temperature and/or increased salinity over the Aegean sea.     

A simple model of summer atmospheric circulation in the Po Valley

Summary Through numerical integration of the primitive equations, we study the summer circulation in the Po Valley, Italy. We investigate separately the mountain slope effect and the sea-breeze effect. The results show that, because of the mountain slope, there is convergence early in the morning and divergence during the day in the lower atmosphere. Further-more, the sea breeze generated by the Adriatic Sea is confined to the eastern side of the Valley. These two phenomena are expected. However, the model suggests that the convergence due to the slope is organized in an area as large as the valley and that, even if the sea breeze is a boundary layer circulation, the perturbation introduced triggers a train of gravity waves as deep as the troposphere. These effects might be very important for the distribution of the summer thunderstorms. Further specific investigations. Experimental and theoretical, are needed. Paper presented at the 1° Congresso del Gruppo Nazionale per la Fisica dell'At-mosfera dell'Oceano, June 19–22, 1984, Rome.     

深海中利用单水听器的影区声源无源测距测深方法

在典型深海情况下当声源与接收水听器位于海水表层时,在影区内由声源海底接收器、声源海面海底接收器、声源海底海面接收器和声源海面海底海面接收器4条声线形成声场干涉结构,声强随着频率具有两种干涉周期,随着收发距离的增加而增大,分别随着声源深度、接收水听器深度的增加而减小。因此由单水听器记录的声场干涉结构即可实现宽带声源目标的无源测距测深,仿真分析验证了其有效性。在南海深海声学实验中观测到海面宽带噪声源在声场影区所形成的声场干涉结构,数据分析结果验证了深海声场干涉结构用于声源无源定位的有效性。与传统无源定位方法相比,该方法不需要宽带引导声源、精确的海底声学参数和大规模的拷贝场计算。