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Modelling of the Svalbard fjord Hornsund

Jakacki J., Przyborska A., Kosecki S., Sundfjord A., Albretsen J.

Oceanologia

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2017

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No. 59 (4)

473--495

EN

The Arctic Ocean is currently in transition towards a new, warmer state. Understanding the regional variability of oceanographic conditions is important, since they have a direct impact on local ecosystems. This work discusses the implementation of a hydrodynamic model for Hornsund, the southernmost fjord of western Svalbard. Despite its location, Hornsund has a stronger Arctic signature than other Svalbard fjords. The model was validated against available data, and the seasonal mean circulation was obtained from numerical simulations. Two main general circulation regimes have been detected in the fjord. The winter circulation represents a typical closed fjord system, while in summer the fresh water discharge from the catchment area generates a surface layer with a net flow out of Hornsund. Also described are the local hydrographic front and its seasonal variability, as well as the heat and salt content in Hornsund. The integration of salt and heat anomalies provides additional information about the salt flux into the innermost basin of the fjord - Brepollen during the summer. Extensive in situ observations have been collected in Hornsund for the last two decades but our hydrodynamic model is the first ever implemented for this area. While at the moment in situ observations better represent the state of this fjord's environment and the location of measurements, a numerical model, despite its flaws, can provide a more comprehensive image of the entire fjord's physical state. In situ observations and numerical simulations should therefore be regarded as complementary tools, with models enabling a better interpretation and understanding of experimental data.

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eBalticGrid – an interactive platform for the visualisation of results from a high-resolution operational Baltic Sea model

Jakacki J., Przyborska A., Nowicki A., Wichorowski M., Przyborski M., Białoskórski M., Sochacki C., Tylman R.

Meteorology Hydrology and Water Management. Research and Operational Applications

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2017

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Vol. 5, Iss. 2

13--20

EN

In recent years, modelling has been one of the fastest growing fields of science. Ocean, ice and atmospheric models have become a powerful tool that has supported many scientific fields during the last few decades. Our work presents the new operational service – called eBalticGrid – implemented into the PLGrid Infrastructure (Dziekoński et al. 2014). The grid is based on three modelling tools – an ocean model (Parallel Ocean Program), an ice model (Community Ice Code) and an atmospheric model (Whether Research and Forecasting Model). The service provides access to 72-hour forecasts for the Baltic Sea area. It includes the physical state of the Baltic Sea, its ice cover and the main atmospheric fields, which are the key drivers of the Baltic’s physical state. Unlike other services, this provides the additional three-dimensional fields of temperature, salinity and currents in the Baltic Sea. The models work in operational mode and currently one simulation per day is run. The service has been implemented mostly for researchers. Access to the results does not require any modelling knowledge. Therefore, the main interface between a user and the model results was designed as a portal providing easy access to the model’s output. It will also be a very suitable tool for teaching students about the hydrology of the Baltic Sea. Data from the system are delivered to another operational system – SatBaltic (Woźniak et al. 2011). The development of an output format to be suitable for navigational software (GRIB files) and sharing via FTP is also planned.

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Groundwater flow due to a nonlinear wave set-up on a permeable beach

Przyborska A.

Oceanologia

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2014

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No. 56 (3)

477--496

EN

Water flow through the beach body plays an important role in the biological status of the organisms inhabiting the beach sand. For tideless seas, the groundwater flow in shallow water is governed entirely by the surface wave dynamics on the beach. As waves propagate towards the shore, they become steeper owing to the decreasing water depth and at some depth, the waves lose their stability and start to break. When waves break, their energy is dissipated and the spatial changes of the radiation stress give rise to changes in the mean sea level, known as the set-up. The mean shore pressure gradient due to the wave set-up drives the groundwater circulation within the beach zone. This paper discusses the circulation of groundwater resulting from a nonlinear set-up. The circulation of flow is compared with the classic Longuet-Higgins (1983) solution and the time series of the set-up is considered for a 24 h storm. Water infiltrates into the coastal aquifer on the upper part of the beach near the maximum run-up and exfiltration occurs on the lower part of the beach face near the breaking point.

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Surface wave generation due to glacier calving

Massel S.R., Przyborska A.

Oceanologia

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2013

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No. 55 (1)

101-127

EN

Coastal glaciers reach the ocean in a spectacular process called "calving". Immediately after calving, the impulsive surface waves are generated, sometimes of large height. These waves are particularly dangerous for vessels sailing close to the glacier fronts. The paper presents a theoretical model of surface wave generation due to glacier calving. To explain the wave generation process, four case studies of ice blocks falling into water are discussed: a cylindrical ice block of small thickness impacting on water, an ice column sliding into water without impact, a large ice block falling on to water with a pressure impulse, and an ice column becoming detached from the glacier wall and falling on to the sea surface. These case studies encompass simplified, selected modes of the glacier calving, which can be treated in a theoretical way. Example calculations illustrate the predicted time series of surface elevations for each mode of glacier calving.

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Attenuation of wave-induced groundwater pressure in shallow water. Part 2. Theory

Massel S. R., Przyborska A., Przyborski M.

Oceanologia

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2005

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No. 47 (3)

291-323

EN

In this Part 2 of the paper (Part 1 was published by Massel et al. 2004) an exact close-form solution for the pore-water pressure component and velocity circulation pattern induced by surface waves is developed. This comprehensive theoretical model, based on Biot's theory, takes into account soil deformations, volume change and pore-water flow. The calculations indicate that for the stiffness ratio G/E'w ? 100, the vertical distribution of the pore pressure becomes very close to the Moshagen & T?rum (1975) approach, when the soil is rigid and the fluid is incompressible. The theoretical results of the paper have been compared with the experimental data collected during the laboratory experiment in the Large Wave Channel in Hannover (see Massel et al. 2004) and showed very good agreement. The apparent bulk modulus of pore water was not determined in the experiment but was estimated from the best fit of the experimental pore-water pressure with the theoretical one. In the paper only a horizontal bottom is considered and the case of an undulating bottom will be dealt with in another paper.

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Attenuation of wave-induced groundwater pressure in shallow water. Part 1

Massel S. R., Przyborska A., Przyborski M.

Oceanologia

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2004

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No. 46 (3)

383-404

EN

A coastal aquifer has a dynamic seaward boundary at the beach face where physical and ecological processes are influenced by oceanic water level fluctuations. Many basic groundwater concepts and the role of the impact of groundwater seepage on beach ecosystems are still poorly understood. Studies are needed to improve our understanding of the relationships between surface and subsurface flow processes on beaches. This is particularly helpful in clarifying the interaction of the physical processes, biodiversity and productivity of sandy beaches, sediment transport and coastal structure stability and modern beach nourishment techniques. As the estimation of infiltration into beach sand is very difficult to carry out under real sea conditions, a control led large-scale laboratory experiment was carried out in the Large Wave Channel in Hannover (Germany) as part of a project supported by the European Community (contract HPRI-CT-2001-00157). First part of the paper describes the technology applied in the experiment and reports some preliminary results.