196 research outputs found

    Run-up characterstics of symmetrical solitary tsunami waves of unknown shapes

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    The problem of tsunami wave run-up on a beach is discussed in the framework of the rigorous solutions of the nonlinear shallow-water theory. We present an analysis of the run-up characteristics for various shapes of the incoming symmetrical solitary tsunami waves. It will be demonstrated that the extreme (maximal) wave characteristics on a beach (run-up and draw-down heights, run-up and draw-down velocities and breaking parameter) are weakly dependent on the shape of incident wave if the definition of the significant wave length determined on the 2/3 level of the maximum height is used. The universal analytical expressions for the extreme wave characteristics are derived for the run-up of the solitary pulses. They can be directly applicable for tsunami warning because in many case the shape of the incident tsunami wave is unknown.Comment: Submitted to PAGEOP

    Coupling coefficients and kinetic equation for Rossby waves in multi-layer ocean

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    International audienceThe kinetic description of baroclinic Rossby waves in multi-layer model ocean is analysed. Explicit analytical expressions for the coupling coefficients describing energy exchange intensity between different modes are obtained and their main properties are established for the three-layer model. It is demonstrated that several types of interactions vanish in the case of simple vertical structures of the ocean, e.g. when all layers have equal depth. These cases correspond to a zero component of the eigenvectors of the potential vorticity equations. The kinetic equation always possesses a fully barotropic solution. If energy is concentrated in the baroclinic modes, the barotropic mode will necessarily be generated. Motion systems consisting of a superposition of the barotropic and a baroclinic mode always transfer energy to other baroclinic modes

    Modelling of wave climate and sediment transport patterns at a tideless embayed beach, Pirita Beach, Estonia

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    Nearshore sand transport patterns along the tideless, embayed Pirita beach, Tallinn, Estonia, have been investigated utilizing high-resolution modelling of wave processes combined with bathymetric surveys and sediment textural analyses of the nearshore sea floor. Textural analysis showed the mean grain size is about 0.12 mm. Fine sand (0.063–0.125 mm) accounts for about 77% of the sediments. Coarser-grained sand (0.28 mm) dominates along the waterline. Based upon the spatial distribution of the mean grain size and basic features of the local wave activity, properties of the Dean Equilibrium Beach Profile were determined. Alongshore sediment transport was calculated based upon a long-term time series of wave properties along the beach, and the CERC formula applied to about 500 m long beach sectors. The time series of wave fields and the properties of the local wave climate were modelled using a triple nested WAM wave model with an extended spectral range for short waves. The model is forced by open sea wind data from Kalbådagrund for the years 1981–2002. Results indicate that typical closure depth at Pirita is 2.5 m. The width and mean slope of the equilibrium profile are 250 m and 1:100, respectively. Southward transport dominates in the northern sections of the beach whereas no prevailing transport direction exists in the southern sections. This pattern has several nontrivial implications for the planning of beach protection activities

    Shifts in early spring wind regime in North-East Europe (1955?2007)

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    International audienceChanges of the winter-to-spring switch-time of the upper air flow regime at 850 and 500 hPa levels over the north-eastern Baltic Sea are analyzed based on a data set extending until 2007. The long-term variation of the air flow in early spring (March) exhibits multiple regime shifts. The shifts are extracted by means of a vector analysis of the monthly mean air flow as well as the statistical shift detection technology. In the middle of the 1960s the average air flow turned from NW (WNW) to W (WSW) at the 500 (850) hPa level. The original regime was restored in the mid-1990s. The regime shifts in the average air flow in March can be interpreted as changes in the transition time from winter to summer circulation type

    Changes in wave dynamics at the south-eastern coast of the Baltic Proper during 1993–2008

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    Using data gathered by visual wave observations at three Lithuanian coastal observation sites during 1993-2008, we make an attempt to relate the recent changes in the intensity of coastal processes on the Lithuanian coast to changes in the local wave regime. There exist considerable interannual variations in the overall wave activity but no statistically significant trends in wave heights for the study period. The directional distribution of wave approach directions has become considerably narrower since about 2002. This feature is most prominent at Palanga where since 2002 almost all waves have approached from SW. This change apparently leads to a decrease in the sediment supply to the Curonian Spit and to a certain starvation of the Lithuanian coast
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