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  • 341.
    Funquist, Lennart
    et al.
    SMHI, Research Department, Oceanography.
    Kleine, Eckhard
    SMHI.
    Application of the BSH model to Kattegat and Skagerrak1995Report (Other academic)
  • 342.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Nyberg, Leif
    SMHI.
    A coupled ice-ocean model supporting winter navigation in the Baltic Sea: Part 2. Thermodynamics and meteorological coupling1995Report (Other academic)
  • 343. 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.

  • 344.
    Rahm, Lars
    et al.
    SMHI, Research Department, Oceanography.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    LARSSON, P
    FOGELQVIST, E
    BREMLE, G
    Valderaama, Jorge
    SMHI.
    NUTRIENT AND PERSISTENT POLLUTANT DEPOSITION ON THE BOTHNIAN BAY ICE AND SNOW FIELDS1995In: Water, Air and Soil Pollution, ISSN 0049-6979, E-ISSN 1573-2932, Vol. 84, no 1-2, p. 187-201Article in journal (Refereed)
    Abstract [en]

    A study of atmospheric deposited nutrients and some persistent pollutants has been carried out on the ice and snow fields of the subarctic Bothnian Bay, the northernmost basin of the Baltic Sea. Total amounts of 600, 500 and 400 tons NO3-N, NH4-N and N-org-N, respectively are deposited in the snow while the corresponding amounts for P-tot-P is 40 tons. The corresponding amount for PCB and lindane are 1.0 and 0.2 kg, respectively. The measurements were carried out on the snow-covered ice four to six weeks old. A part of the deposited snow has been incorporated into the snow-ice and an attempt to estimate its mean thickness and its amount of nutrients has been made. The total amounts now reach 1700, 1300 and 1100 tons of NO3-N and NH4-N and N-org-N, respectively in the snow and ice together. The results obtained support the use of land-based stations in estimates of seasonal atmospheric nutrient deposition to the Bothnian Bay. The observed concentrations of chloroorganic compounds correspond to those land-based observations reported from the same latitude in the northern hemisphere and reported in literature.

  • 345.
    Håkansson, Bertil
    et al.
    SMHI, Research Department, Oceanography.
    Moberg, Mats
    SMHI.
    Thompson, Thomas
    SMHI.
    REAL-TIME USE OF ERS-1 SAR IMAGERY FOR ICE SERVICE AND ICEBREAKING OPERATIONS IN THE BALTIC SEA1995In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 16, no 17, p. 3441-3458Article in journal (Refereed)
    Abstract [en]

    Sea ice forms every winter in the Baltic Sea and several icebreakers in Sweden and Finland keep the major ports in the area open for sea-trade all the year around. Information and forecasts of the sea ice formation, drift and deformation are vital for safe and efficient winter navigation. In this respect, Synthetic Aperture Radar (SAR) imagery is of great interest, since this technique is almost cloud independent and has potential for real-time ice mapping. The usefulness of SAR imagery for sea ice operations has been evaluated in the Baltic Sea. The imagery was used both for ice mapping, for icebreaker operations and ship routeing. Images presented onboard the icebreakers were highly appreciated and easily interpreted by the crew. The data were frequently used for ship routeing (33 per cent) of merchant vessels and for direct icebreaker assistance (53 per cent). It was concluded by several icebreaker masters that an image resolution of about 100 m was indeed enough to distinguish ridged areas and in the same time obtain a large enough geographical coverage per image.

  • 346. MACDONALD, RW
    et al.
    PATON, DW
    CARMACK, EC
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    THE FRESH-WATER BUDGET AND UNDER-ICE SPREADING OF MACKENZIE RIVER WATER IN THE CANADIAN BEAUFORT SEA BASED ON SALINITY AND O-18/O-16 MEASUREMENTS IN WATER AND ICE1995In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 100, no C1, p. 895-919Article in journal (Refereed)
    Abstract [en]

    Observations of salinity and oxygen isotope composition (delta(18)O) were made for the Beaufort shelf-Mackenzie estuary waters in September 1990, just prior to ice formation, and for both the water column and ice in April-May 1991, at the end of winter. These measurements are used to determine the apportioning of fresh water in the estuary between its two main sources, runoff and sea ice melt. Changes in disposition of water between seasons and amounts frozen into the growing ice sheet are also derived. Two domains are considered in order to construct a freshwater budget for the Mackenzie shelf, the nearshore within which landfast ice grows in winter and the outer shelf. Most of the winter inflow from the Mackenzie River appears to remain impounded as liquid under the ice within the landfast zone at the end of winter, and about 15% of it is incorporated into the landfast ice. Oxygen isotopes (delta(18)O) in ice cores collected from across the shelf record the progress beneath the ice of new Mackenzie inflow as it invades the nearshore throughout winter. Rates of spreading are about 0.2 cm s(-1) away from the coast and 1.3 cm s(-1) along the coast. As this inflow spreads across the shelf, it progressively shuts off convection driven by brine production at locations within the landfast ice. Salinity and delta(18)O in the offshore water column suggest that about 3 m of sea ice was for:med in the outer shelf domain. Since both brine and newly formed sea ice can be advected off the shelf, a complete budget for brine or sea ice production cannot be established without first measuring the advection of one of these two components.

  • 347.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Nyberg, Leif
    SMHI.
    Leppäranta, Matti
    Univ. of Helsinki. Dep. of geophysics.
    A coupled ice-ocean model supporting winter navigation in the Baltic Sea: Part 1. Ice dynamics and water levels1994Report (Other academic)
  • 348.
    Håkansson, Bertil
    et al.
    SMHI, Research Department, Oceanography.
    Moberg, Mats
    SMHI.
    THE ALGAL BLOOM IN THE BALTIC DURING JULY AND AUGUST 1991, AS OBSERVED FROM THE NOAA WEATHER-SATELLITES1994In: International Journal of Remote Sensing, ISSN 0143-1161, E-ISSN 1366-5901, Vol. 15, no 5, p. 963-965Article in journal (Refereed)
  • 349.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    CARMACK, EC
    MACDONALD, RW
    MODELING THE SEASONAL CYCLE OF SALINITY IN THE MACKENZIE SHELF ESTUARY1994In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 99, no C5, p. 10011-10021Article in journal (Refereed)
    Abstract [en]

    The freshwater content at the Mackenzie shelf/estuary is analyzed using observed and numerically simulated data. Field measurements cover the period from September 1986 to September 1987; calculations are based upon a time-dependent, one-dimensional model that treats the shelf as a single reservoir coupled to the surroundings through parameterizations of the inflows and outflows. The system is assumed to be controlled by transient Ekman flow dynamics, and forced by winds when the sea is ice free, and by tides when ice covered. Buoyancy fluxes due to river inflow, freezing and melting of ice, and outflow are added to the salinity conservation equation from which the freshwater content is calculated. Sensitivity studies from simulation of the 1986-1987 period show that the freshwater content of the Mackenzie shelf/estuary is highly influenced by freezing, ice advection off the shelf, and the wind-driven transport, all of which work effectively to remove fresh water from the shelf. Ice keels in the inner shelf may also reduce the export of fresh water to the outer shelf. The sensitivity of the system to altered river inflow from either hydroelectric development or climate change is also examined. For example, upstream storage would increase winter inflows and thus decrease the shelf's capacity to ventilate the halocline, while inflow reduction would enhance shelf ventilation.

  • 350.
    Svensson, Urban
    et al.
    SMHI, Research Department, Oceanography.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    SIMULATION OF SUPERCOOLING AND SIZE DISTRIBUTION IN FRAZIL ICE DYNAMICS1994In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 22, no 3, p. 221-233Article in journal (Refereed)
    Abstract [en]

    The objective of the work presented is to formulate a mathematical description of frazil ice dynamics. The formulation is to be in balance with the current knowledge of the physical processes, for example secondary nucleation. As the knowledge of some of these processes is fragmentary, this means that a conceptually simple formulation is sought. A number of processes are known to influence the supercooling rate and the frazil ice production. The present formulation accounts for the following processes: initial seeding, secondary nucleation, gravitational removal, growth due to cooling of water volume and flocculation/break up. Equations are formulated for these present considering a resolution in time and radius of particles but not in space (well-mixed jar). The equations are solved using a simple explicit numerical scheme. Preliminary results indicate that the model can be calibrated to describe the experimental results reported in the literature. It is mainly the supercooling curves that are used for comparison but some information about the crystal size distribution is also considered. It is to be noted that the model is calibrated to fit the experiments, due to the lack of detailed mathematical description of some of the physical processes. Sensitivity analysis is also used in order to establish that the model behaves according to experimental findings and expectations. The main conclusion of the study is that a fairly simple mathematical model can be formulated and calibrated, which fits the experimental data reported in the literature hitherto. It is further concluded that a resolution in radial space gives additional insight into the dynamics of the process. The evolution of the size distribution and its sensitivity to seeding and dissipation rate has been predicted with results that look physically plausible.

  • 351.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    MURTHY, CR
    ON CURRENTS AND VERTICAL MIXING IN LAKE-ONTARIO DURING SUMMER STRATIFICATION1994In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 25, no 3, p. 213-232Article in journal (Refereed)
    Abstract [en]

    Currents and vertical mixing characteristics were investigated on the basis of time series of current meter and temperature data from a summer-stratified period in Lake Ontario. The experimental set up consisted of seven current meters distributed in one vertical line from 12 m below the surface to 1 m above the lake bottom at a total depth of 143 m. The period considered for the analysis was from June to September, 1991. The currents showed pronounced oscillations with two significant kinetic energy peaks, one at about 17 hours due to inertial motions, and one at 10 days, probably due to meteorological forcing. The current shear in the hypolimnion was strong enough to overcome stability and generate turbulence (Richardson numbers below 0.25) and there was probably turbulence enough available to keep the matter (almost neutral buoyant particles) in the whole Nepheloid bottom layer in suspension. In the thermocline region the turbulence was mainly damped (Richardson numbers above 1), but some events with lower Richardson numbers were also calculated indicating increased mixing during these events. By analysing filtered and unfiltered current meter data it was found that the shear-generated turbulence in the hypolimnion was mainly due to the meteorologically forced currents. In the thermocline region, however, the vertical shear associated with the inertial oscillation had a greater impact on the mixing.

  • 352.
    Funquist, Lennart
    SMHI, Research Department, Oceanography.
    An operational Baltic Sea circulation model: Part 1. Barotropic version1993Report (Other academic)
  • 353.
    Andersson, Lars
    et al.
    SMHI, Core Services.
    Edler, Lars
    SMHI, Research Department, Oceanography.
    Sjöberg, Björn
    SMHI, Core Services.
    The conditions of the seas around Sweden: Report from activities in 19921993Report (Other academic)
  • 354.
    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.

  • 355.
    Thompson, Thomas
    et al.
    SMHI.
    Ulander, Lars
    SMHI.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Brusmark, Bertil
    SMHI.
    Carlström, Anders
    SMHI.
    Gustavsson, Anders
    SMHI.
    BEERS -92: Final edition1992Report (Other academic)
  • 356.
    Murthy, Ray
    et al.
    Nat. Water Res., Inst. Canada Centre for Inland Waters. Burlington, Ontario.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Alenius, Pekka
    Finnish Inst. of Marine Res. Helsinki.
    The Gulf of Bothnia Year-1991 – Physical transport experiments1992Report (Other academic)
  • 357.
    Andersson, Lars
    et al.
    SMHI, Core Services.
    Carlberg, Stig
    SMHI, Core Services.
    Edler, Lars
    SMHI, Research Department, Oceanography.
    Fogelqvist, Elisabet
    SMHI.
    Fonselius, Stig
    SMHI, Research Department, Oceanography.
    Fyrberg, Lotta
    SMHI, Core Services.
    Palmén, Håkan
    SMHI.
    Sjöberg, Björn
    SMHI, Core Services.
    Zagradkin, Danuta
    SMHI.
    Haven runt Sverige 1991. Rapport från SMHI, Oceanografiska Laboratoriet, inklusive PMK - utsjöprogrammet: The conditions of the seas around Sweden. Report from the activities in 1991, including PMK - The National Swedish Programme for Monitoring of Environmental Quality Open Sea Programme1992Report (Other academic)
  • 358.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    WETTLAUFER, JS
    ICE GROWTH AND OCEANIC HEAT-FLUX - MODELS AND MEASUREMENTS1992In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 97, no C6, p. 9383-9390Article in journal (Refereed)
    Abstract [en]

    Heat fluxes al the ice-ocean interface and ice thickness are investigated by comparing field data from the Coordinated Eastern Arctic Experiment (CEAREX) drift phase with model calculations. The calculations are based on two types of models. The first one is a one-dimensional ice-ocean model with high vertical resolution. This model is based on the conservation equations for heat, salt, and momentum and uses turbulence models to achieve closure. A discrete element approach is also introduced to explicitly parameterize the ice roughness. The second model is a simple one-dimensional bulk heat transfer model. In this version, the interfacial salinity is modelled on the basis of salt conservation at the ice-ocean interface. The bulk heat transfer model is then calibrated using the former model. The two models predict ocean heat fluxes that are quite variable in time owing to short-term variations in the ice drift. Both models calculate realistic ice thicknesses. It is demonstrated that the observed time variation in ice thickness from eight different experimental sites with varying initial thicknesses and bottom topographies can be reproduced by applying bulk heat transfer coefficients in the range (2.8 +/- 1) x 10(-4). Horizontal variation of the thermal state within a single pack ice floe results in simultaneous freezing and melting over relatively small spatial scales. When modeling or averaging ice data in space these aspects need to be considered.

  • 359. 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.

  • 360.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Svensson, Urban
    SMHI, Research Department, Oceanography.
    ON THE MELT RATE OF DRIFTING ICE HEATED FROM BELOW1992In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 21, no 1, p. 91-100Article in journal (Refereed)
    Abstract [en]

    The melt rates of fresh and saline drifting ice, heated from below, are examined using a one-dimensional ice/ocean model with high vertical resolution. The model is based on the conservation equations for heat, salt, and momentum and uses turbulence models to achieve closure. The model includes a low-Reynolds number turbulence model for the viscous region, coupled to a high-Reynolds number turbulence model for the outer boundary, and a discrete element approach to the parameterization of roughness. It is shown that the melt rate of drifting ice is sensitive to ice roughness and molecular salt diffusion, and it is found that bulk heat transfer coefficients vary within a rather narrow range in the examined interval.

151617181920 341 - 360 of 398
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