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  • 1. ENGQVIST, A
    et al.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    WATER EXCHANGE AND DENSITY STRUCTURE IN A MULTIBASIN ESTUARY1992In: Continental Shelf Research, ISSN 0278-4343, E-ISSN 1873-6955, Vol. 12, no 9, p. 1003-1026Article in journal (Refereed)
    Abstract [en]

    A mathematical model of the Himmerfjard estuary. divided into four basins. has been formulated and validated against measured data for 1986. The structure of each sub-basin is assumed to be horizontally homogeneous with vertical mean velocities based upon in- and outflows from adjacent basins and freshwater supply to each basin. The horizontal water exchange is formulated as a quasi-stationary Bernioulli flow, driven by horizontal pressure gradients over the sounds and instantaneously interleaved at a neutral buoyancy level. Thc salinity and temperature profiles measured outside the mouth of the estuary serve as forcing, as do the water level changes, the freshwater run-off and the local wind. Inherent in the model assumptions of the horizontal exchange over the sounds is that only a fraction, alpha, of the pressure gradient is used to accelerate each stratum. Variation of the alpha-value shows that the best statistical fit is found for alpha = 0.15 when compared with water exchange estimates based on measurements in one of the internal sounds tor almost an entire month. Using this alpha-value, in combination with standard mixing parameters and hypsographical data, the model satisfactorily captures the major features of the salinity and temperature-profiles development for the year 1986. This is substantiated by statistical analysis of the salinity profiles in the sub-basins for which different measures of similarity between simulated and measured data give the best fit for the same alpha-value as above.

  • 2.
    Hordoir, Robinson
    et al.
    SMHI, Research Department, Oceanography.
    Dieterich, Christian
    SMHI, Research Department, Oceanography.
    Basu, Chandan
    Dietze, Heiner
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Freshwater outflow of the Baltic Sea and transport in the Norwegian current: A statistical correlation analysis based on a numerical experiment2013In: Continental Shelf Research, ISSN 0278-4343, E-ISSN 1873-6955, Vol. 64, p. 1-9Article in journal (Refereed)
    Abstract [en]

    Based on the results of a numerical ocean model, we investigate statistical correlations between wind forcing, surface salinity and freshwater transport out of the Baltic Sea on one hand, and Norwegian coastal current freshwater transport on the other hand. These correlations can be explained in terms of physics and reveal how the two freshwater transports are linked with wind forcing, although this information proves to be non-sufficient when it comes to the dynamics of the Norwegian coastal current. Based on statistical correlations, the Baltic Sea freshwater transport signal is reconstructed and shows a good correlation but a poor variability when compared with the measured signal, at least when data filtered on a two-daily time scale is used. A better variability coherence is reached when data filtered on a weekly or monthly time scale is used. In the latest case, a high degree of precision is reached for the reconstructed signal. Using the same kind of methods for the case of the Norwegian coastal current, the negative peaks of the freshwater transport signal can be reconstructed based on wind data only, but the positive peaks are under-represented although some of them exist mostly because the meridional wind forcing along the Norwegian coast is taken into account. Adding Norwegian coastal salinity data helps improving the reconstruction of the positive peaks, but a major improvement is reached when adding non-linear terms in the statistical reconstruction. All coefficients used to re-construct both freshwater transport signals are provided for use in European Shelf or climate modeling configurations. (c) 2013 Elsevier Ltd. All rights reserved.

  • 3. KAHRU, M
    et al.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    RUD, O
    DISTRIBUTIONS OF THE SEA-SURFACE TEMPERATURE FRONTS IN THE BALTIC SEA AS DERIVED FROM SATELLITE IMAGERY1995In: Continental Shelf Research, ISSN 0278-4343, E-ISSN 1873-6955, Vol. 15, no 6, p. 663-679Article in journal (Refereed)
    Abstract [en]

    A 9-month time series of satellite infrared imagery was used to examine the sea surface temperature (SST) variability in the northern and central Baltic Sea. Objective multi-level edge detection techniques were applied to find sharp SST gradient areas known as fronts. The spatial distribution of frontal frequency was calculated over time periods from a few days to 9 months covering different thermal and wind conditions. The 9-month average frequency that a front is detected in a pixel of 1.1 x 1.1 km is up to 10% in certain areas whereas the median is around 2%. Large scale fronts are aligned to the coast and isobaths, and occur predominantly in areas of straight and uniformly sloping bottom topography. The major frontal areas are along the eastern coast of the Bothnian Sea and along the north-western coast of the Gulf of Finland. Low large-scale frontal frequency is characteristic to areas with highly structured bottom topography. The major mechanism of front generation is coastal upwelling, being complemented by coastal jets, eddies, differential heating and cooling, and water exchange between basins with different water characteristics. Filaments (''squirts'') originating from upwelling areas are shown to be an important mechanism for transporting water and substances over long distances.

  • 4.
    Marmefelt, Eleonor
    et al.
    SMHI, Professional Services.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    DEEP-WATER PROPERTIES IN THE GULF OF BOTHNIA1993In: Continental Shelf Research, ISSN 0278-4343, E-ISSN 1873-6955, Vol. 13, no 2-3, p. 169-187Article in journal (Refereed)
    Abstract [en]

    The northern extension of the Baltic Sea, the Gulf of Bothnia, is a weakly stratified sea. One would therefore expect that the deep water of the Gulf is easily renewed through deep thermal convection, or even through deep haline convection, as the Gulf is more or less covered with ice every winter. However, the present study shows, through analysis of historical temperature, salinity and density data, that the deep water in the Gulf of Bothnia is mainly renewed by major inflows of Baltic Proper surface water. The penetrating water forms a dense bottom current in the Gulf. In the southern part of the Gulf, the Bothnian Sea, the volume flow of the bottom current is found to increase by 10%. It is therefore not likely that the bottom current properties are changed to any appreciable extent. The bottom current properties in the Bothnian Bay, on the other hand, are highly affected, as the volume flow is estimated to increase by 150% in this basin.

  • 5.
    Omstedt, Anders
    et al.
    Göteborgs Universitet.
    Axell, Lars
    SMHI, Research Department, Oceanography.
    Modeling the variations of salinity and temperature in the large Gulfs of the Baltic Sea2003In: Continental Shelf Research, ISSN 0278-4343, E-ISSN 1873-6955, Vol. 23, no 3-4, p. 265-294Article in journal (Refereed)
    Abstract [en]

    The modeling of salinity and temperature in Gulf of Bothnia, Gulf of Finland, and Gulf of Riga is investigated by using a coupled sea ice-ocean Baltic Sea model. 18 years, from late 1980 to the end of 1998, have been investigated. The forcing data extracted taken from a gridded meteorological data base, sea level data from the Kattegat, and river runoff data to the different subbasins of the Baltic Sea from a hydrological data base. To improve the gridded meteorological data base a statistical model for the reduction of geostrophic winds to surface winds was developed. In the analysis it was shown that the calculated long-term salinity and temperature structures were stable and in good agreement with observations. This was made possible by using three different strait-flow models connecting the subbasins of the Baltic Sea. The seasonal and interannual variations of temperature and salinity were also well simulated by the model, implying that the coupling between the atmosphere and the Baltic Sea as well as the diapycnal mixing are reasonably well understood. The water cycle and the surface heat balance were calculated using the 18-year simulation. In the water-balance calculations it was shown that the volume flows from the large gulfs of the Baltic Sea were mainly due to baroclinic transports and that net precipitation added freshwater during the Studied period, particularly to the large gulfs. From the heat-balance calculation it is concluded that the Baltic Sea is almost in local balance with the atmosphere. The Bothnian Bay, Gulf of Finland and Gulf of Riga loose heat, whereas the Bothnian Sea gains heat, calculated as long-term means. (C) 2003 Elsevier Science Ltd. All rights reserved.

  • 6. Omstedt, Anders
    et al.
    Edman, Moa
    SMHI, Research Department, Oceanography.
    Claremar, Bjorn
    Rutgersson, Anna
    SMHI, Research Department, Climate research - Rossby Centre.
    Modelling the contributions to marine acidification from deposited SOx, NOx, and NHx in the Baltic Sea: Past and present situations2015In: Continental Shelf Research, ISSN 0278-4343, E-ISSN 1873-6955, Vol. 111, p. 234-249Article in journal (Refereed)
    Abstract [en]

    We have examined the effects of historical atmospheric depositions of sulphate, nitrate, and ammonium from land and shipping on the acid-base balance in the Baltic Sea. The modelling considers the 1750-2014 period, when land and ship emissions changed greatly, with increasing carbon dioxide concentrations, SOx, NOx, and NHx emissions, and nutrient loads. The present results indicate that Baltic Sea acidification due to the atmospheric deposition of acids peaked around 1980, with a pH cumulative decrease of approximately 10(-2) in surface waters. This is one order of magnitude less than the cumulative acidification due to increased atmospheric CO2. The acidification contribution of shipping is one order of magnitude less than that of land emissions. However, the pH trend due to atmospheric acids has started to reverse due to reduced land emissions, though the effect of shipping is ongoing. The effect of strong atmospheric acids on Baltic Sea water depends on the region and period studied. The largest total alkalinity sink per surface area is in the south-western Baltic Sea where shipping is intense. Considering the entire Baltic Sea over the 2001-2010 period, the pH changes are approximately -3 x 10(-3) to -11 x 10(-3) and -4 x 10(-4) to -16 x 10(-4) pH units attributable to all emissions and ship emissions only, respectively. The corresponding changes in total alkalinity are approximately -10 to -30 mu mol kg(-1) and -1 to -4 mu mol kg(-1) attributable to all emissions and ship emissions only, respectively. (C) 2015 Elsevier Ltd. All rights reserved.

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