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  • 1.
    Axell, Lars
    SMHI, Research Department, Oceanography.
    Wind-driven internal waves and Langmuir circulations in a numerical ocean model of the southern Baltic Sea2002In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, no C11, article id 3204Article in journal (Refereed)
    Abstract [en]

    [1] A one-dimensional numerical ocean model of the southern Baltic Sea is used to investigate suitable parameterizations of unresolved turbulence and compare with available observations. The turbulence model is a k-epsilon model that includes extra source terms P-IW and P-LC of turbulent kinetic energy (TKE) due to unresolved, breaking internal waves and Langmuir circulations, respectively. As tides are negligible in the Baltic Sea, topographic generation of internal wave energy (IWE) is neglected. Instead, the energy for deepwater mixing in the Baltic Sea is provided by the wind. At each level the source term P-IW is assumed to be related to a vertically integrated pool of IWE, E-0, and the buoyancy frequency N at the same level, according to P-IW (z) proportional to E0Ndelta (z). This results in vertical profiles of epsilon (the dissipation rate of TKE) and K-h (the eddy diffusivity) according to epsilon proportional to N-delta and K-h proportional to Ndelta-2 below the main pycnocline. Earlier observations are inconclusive as to the proper value of delta, and here a range of values of delta is tested in hundreds of 10-year simulations of the southern Baltic Sea. It is concluded that delta = 1.0 +/- 0.3 and that a mean energy flux density to the internal wave field of about (0.9 +/- 0.3) x 10(-3) W m(-2) is needed to explain the observed salinity field. In addition, a simple wind-dependent formulation of the energy flux to the internal wave field is tested, which has some success in describing the short- and long-term variability of the deepwater turbulence. The model suggests that similar to16% of the energy supplied to the surface layer by the wind is used for deepwater mixing. Finally, it is also shown that Langmuir circulations are important to include when modeling the oceanic boundary layer. A simple parameterization of Langmuir circulations is tuned against large-eddy simulation data and verified for the Baltic Sea.

  • 2. Bais, A F
    et al.
    Gardiner, B G
    Slaper, H
    Blumthaler, M
    Bernhard, G
    McKenzie, R
    Webb, A R
    Seckmeyer, G
    Kjeldstad, B
    Koskela, T
    Kirsch, P J
    Grobner, J
    Kerr, J B
    Kazadzis, S
    Leszczynski, K
    Wardle, D
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Brogniez, C
    Gillotay, D
    Reinen, H
    Weihs, P
    Svenoe, T
    Eriksen, P
    Kuik, F
    Redondas, A
    SUSPEN intercomparison of ultraviolet spectroradiometers2001In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 106, no D12, p. 12509-12525Article in journal (Refereed)
    Abstract [en]

    Results from an intercomparison campaign of ultraviolet spectroradiometers that was organized at Nea Michaniona, Greece July, 1-13 1997, are presented. Nineteen instrument systems from 15 different countries took part and provided spectra of global solar UV irradiance for two consecutive days from sunrise to sunset every half hour. No data exchange was allowed between participants in order to achieve absolutely independent results among the instruments. The data analysis procedure included the determination of wavelength shifts and the application of suitable corrections to the measured spectra, their standardization to common spectral resolution of 1 nm full width at half maximum and the application of cosine corrections. Reference spectra were calculated for each observational time, derived for a set of instruments which were objectively selected and used as comparison norms for the assessment of the relative agreement among the various instruments. With regard to the absolute irradiance measurements, the range of the deviations from the reference for all spectra was within +/- 20%. About half of the instruments agreed to within +/-5%, while only three fell outside the +/- 10% agreement limit. As for the accuracy of the wavelength registration of the recorded spectra, for most of the spectroradiometers (14) the calculated wavelength shifts were smaller than 0.2 nm. The overall outcome of the campaign was very encouraging, as it was proven that the agreement among the majority of the instruments was good and comparable to the commonly accepted uncertainties of spectral UV measurements. In addition, many of the instruments provided consistent results relative to at least the previous two intercomparison campaigns, held in 1995 in Ispra, Italy and in 1993 in Garmisch-Partenkirchen, Germany. As a result of this series of intercomparison campaigns, several of the currently operating spectroradiometers operating may be regarded as a core group Of instruments, which with the employment of proper operational procedures are capable of providing quality spectral solar UV measurements.

  • 3.
    Eigenheer, Andrea
    et al.
    SMHI, Research Department, Oceanography.
    Quadfasel, D
    Seasonal variability of the Bay of Bengal circulation inferred from TOPEX/Poseidon altimetry2000In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 105, no C2, p. 3243-3252Article in journal (Refereed)
    Abstract [en]

    The circulation in the interior of the Bay of Bengal and of its western boundary current, the East Indian Coastal Current, is inferred from historical ship drift data and from TOPEX/Poseidon altimeter data. The boundary current shows a strong seasonal variability with reversals twice per year that lead the reversal of the local monsoon wind field by several months. On the basis of model simulations it has been suggested that this unusual behavior can be explained by the influence of remotely forced planetary waves. Our data analysis confirms and refines this view by showing the role of topography in the northern bay. We also give an estimate of the relative importance of the different contributions.

  • 4.
    Hordoir, Robinson
    et al.
    SMHI, Research Department, Oceanography.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Freshwater fluxes in the Baltic Sea: A model study2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, article id C08028Article in journal (Refereed)
    Abstract [en]

    The dynamics of "juvenile" freshwater, which is released during spring into the Baltic proper, is studied using a numerical three-dimensional circulation model. Two methods are used. First, freshwater heights are calculated using simulated salinity fields, and their seasonal variability is analyzed. When compared to climatological observations, the model represents the seasonal variability of freshwater heights well. However, the method does not allow a proper study of the dynamics of juvenile freshwater fluxes. Consequently, a second method is used where a passive tracer, which marks freshwater, is utilized. This method provides a better description of the seasonal spreading of juvenile freshwater in the Baltic proper, although further investigations are still necessary to trace juvenile freshwater. The results from this second method show that juvenile freshwater does not reach the center of the Baltic proper before late summer. During one season, only a small amount of juvenile freshwater may reach the entrance of the Baltic Sea. The increased vertical stratification generated by the arrival of juvenile freshwater and the subsequent baroclinic adjustment may trigger the onset of the spring bloom in accordance to earlier suggestions. Further, the seasonal cycle and inter-annual variability of the freshwater outflow from the Baltic Sea are studied. Seasonal changes of the freshwater outflow are closely connected with that of the zonal wind, although the annual mean outflow is given by the total runoff into the Baltic Sea. Thus, the inter-annual variability of the seasonal freshwater outflow maximum is highly correlated with the North Atlantic Oscillation.

  • 5.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    FOCUSED SUN OBSERVATIONS USING A BREWER OZONE SPECTROPHOTOMETER1992In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 97, no D14, p. 15813-15817Article in journal (Refereed)
    Abstract [en]

    Accurate measurements of total ozone at high latitudes during winter have become increasingly important for studies of polar ozone depletion. The direct Sun measurements are the most direct and physically well defined type of measurement of total ozone with Dobson and Brewer spectrophotometers along with the focused Sun measurements. The direct Sun and focused Sun method are influenced by many sources of error at low solar elevations. A large error arises from the addition of radiation scattered from air along the path of the solar beam. A method to correct for this error using the Brewer instrument is described. The method gives reasonably accurate values down to solar elevations of 5-degrees compared to 10-degrees-20-degrees without corrections. This is especially important for high-latitude stations, where the low solar elevations are a limiting factor for accurate measurements of the total ozone particularly during the winter.

  • 6. Kauker, F
    et al.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Modeling decadal variability of the Baltic Sea: 1. Reconstructing atmospheric surface data for the period 1902-19982003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no C8, article id 3267Article in journal (Refereed)
    Abstract [en]

    A statistical model is developed to reconstruct atmospheric surface data for the period 1902-1998 to force a coupled sea ice-ocean model of the Baltic Sea. As the response timescale of the Baltic Sea on freshwater inflow is of the order of 30-40 years, climate relevant model studies should cover at least century-long simulations. Such an observational atmospheric data set is not available yet. We devised a statistical model using a "redundancy analysis'' to reconstruct daily sea level pressure (SLP) and monthly surface air temperature (SAT), dew-point temperature, precipitation, and cloud cover of the Baltic. The predictor fields are daily SLP at 19 stations and monthly coarse gridded SAT and precipitation available for the period 1902 to 1998. The second input is a gridded atmospheric data set, with high resolution in space and time, based on synoptic stations, which is available for the period 1970-2001. Spatial patterns are selected by maximizing predictand variance during the "learning'' period 1980-1998. The remainder period 1970-1979 is used for validation. We found the highest skill of the statistical model for SLP and the lowest skill for cloud cover. For wintertime the dominant modes of variability on the interannual to interdecadal timescales of the reconstruction are discussed. It is shown that the wintertime variability of SLP, SAT, and precipitation is related to well-known atmospheric patterns of the Northern Hemisphere: the North Atlantic Oscillation, the Scandinavia pattern, the East Atlantic/West Russia pattern, and the Barents Sea Oscillation.

  • 7. 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.

  • 8.
    Mattsson, Johan
    SMHI, Research Department, Oceanography.
    Analysis of the exchange of salt between the Baltic and the Kattegat through the Oresund using a three-layer model1996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no C7, p. 16571-16584Article in journal (Refereed)
    Abstract [en]

    The shallowness of the Oresund prevents a continuous inflow of saline Kattegat water to the Baltic. Instead, the salt is exchanged largely by fluctuating barotropic transports. Buffer effects and temporal storage of low-salinity Baltic surface water complicate the exchange. The analysis of salt exchange through the Oresund requires use of a model of the stratification and baroclinically modified exchange processes. In this paper a three-layer model of the Oresund, forced by the exchange with the Kattegat and the Baltic, is formulated and calibrated. Frontal dynamics, necessary to explain the retreat of the uppermost layer, are included. The model is calibrated using genetic algorithms, which provide an efficient and robust optimization method for this kind of model. An analysis of the exchange in view of the model results is presented. The paper also gives estimates of typical mean quantities. For the analyzed period of 11 years (1977-1987) the mean salt outflow rate from the Baltic during outflows is 311,000 kg s(-1) and the mean salt inflow rate to the Baltic during inflows is 500,000 kg s(-1). The net salt outflow from the Baltic is estimated to 19,000 kg s(-1). The mean frontal speed is estimated at 0.25 m s(-1) and the typical required length of an inflow event for high-salinity Kattegat water to reach the Baltic is estimated at 4 days. Further results are also given. In addition, the baroclinic dynamics of the Oresund are discussed.

  • 9.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Modeling the age of Baltic Seawater masses: Quantification and steady state sensitivity experiments2005In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 110, no C2, article id C02006Article in journal (Refereed)
    Abstract [en]

    [1] Ages of Baltic Seawater masses for the period 1903 - 1998 were quantified using a three-dimensional (3-D) coupled ice-ocean model. Therefore an additional Eulerian tracer for the age of seawater was embedded. The age is the time elapsed since a water particle left the sea surface. Median ages of the bottom water between 1 year in the Bornholm Basin and 7 years in the northwestern Gotland Basin were found. During 1903 - 1998 the oldest bottom water of about 11 years appeared at Landsort Deep. In the halocline of the deeper basins a secondary age maximum was calculated. In the eastern Gotland Basin 3 stagnation periods (in the 1920/1930s, 1950/1960s, and 1980/1990s) with ages exceeding 8 years were found. Further, the sensitivities of modeled salinity and age on freshwater supply, wind speed, and amplitude of the sea level in Kattegat were investigated. In steady state the average salinity of the Baltic is most sensitive to perturbations of freshwater inflow. Increased freshwater inflow and wind speed result both in decreased salinity whereas increased amplitude of the Kattegat sea level results in increased salinity. The average age is most sensitive to perturbations of the wind speed. Especially, decreased wind speed causes significantly increased age of the deep water. On the other hand, the impact of changing freshwater or sea level in Kattegat on the average age is comparatively small, suggesting invariance of stability and ventilation in steady state approximately. A simple conceptual model for the Baltic deep water ventilation was applied to explain the 3-D model results.

  • 10.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    On the parameterization of mixing in three-dimensional Baltic Sea models2001In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 106, no C12, p. 30997-31016Article in journal (Refereed)
    Abstract [en]

    As mixing plays a dominant role for the physics of an estuary like the Baltic Sea (seasonal heat storage, mixing in channels, deepwater mixing), different mixing parameterizations for use in three-dimensional (3-D) Baltic Sea models are discussed. Within the Swedish regional climate modeling program, SWECLIM, a 3-D coupled ice-ocean model for the Baltic Sea has been coupled with an improved version of the two-equation k-epsilon turbulence model using a corrected dissipation term, flux boundary conditions to include the effect of a turbulence enhanced layer due to breaking surface gravity waves, and a parameterization for breaking internal waves. Results of multiyear simulations are compared with observations. The seasonal thermocline (the main focus of this paper) is simulated satisfactory. During the stagnation period between 1983 and 1993, simulated salinity in the lower layer of the Baltic Sea decreases as observed. Unsolved problems of the k-epsilon model are discussed. To replace the controversial equation for dissipation, the performance of a hierarchy of k models has been tested and compared with the k-epsilon model. In addition, it is shown that the results of the 1-D turbulence submodel depend very much on the dimensionality of the hydrodynamic model. Using the same turbulence parameterization, vertical velocity shear and density gradients are simulated differently in 1-D column models compared to 3-D ocean circulation models. Finally, the impact of two mixing parameterizations on Baltic Sea climate is discussed.

  • 11.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Faxen, T
    A multiprocessor coupled ice-ocean model for the Baltic Sea: Application to salt inflow2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no C8, article id 3273Article in journal (Refereed)
    Abstract [en]

    Within the Swedish Regional Climate Modeling Program, SWECLIM, a three-dimensional (3-D) coupled ice-ocean model for the Baltic Sea has been developed to simulate physical processes on timescales of hours to decades. The code has been developed based on the massively parallel version of the Ocean Circulation Climate Advanced Modeling (OCCAM) project of the Bryan-Cox-Semtner model. An elastic-viscous-plastic ice rheology is employed, resulting in a fully explicit numerical scheme that improves computational efficiency. An improved two-equation turbulence model has been embedded to simulate the seasonal cycle of surface mixed layer depths as well as deepwater mixing on decadal timescale. The model has open boundaries in the northern Kattegat and is forced with realistic atmospheric fields and river runoff. Optimized computational performance and advanced algorithms to calculate processor maps make the code fast and suitable for multi-year, high-resolution simulations. As test cases, the major salt water inflow event in January 1993 and the stagnation period 1980-1992, have been selected. The agreement between model results and observations is regarded as good. Especially, the time evolution of the halocline in the Baltic proper is realistically simulated also for the longer period without flux correction, data assimilation, or reinitialization. However, in particular, smaller salt water inflows into the Bornholm Basin are underestimated, independent of the horizontal model resolution used. It is suggested that the mixing parameterization still needs improvements. In addition, a series of process studies of the inflow period 1992/1993 have been performed to show the impact of river runoff, wind speed, and sea level in Kattegat. Natural interannual runoff variations control salt water inflows into the Bornholm Basin effectively. The effect of wind speed variation on the salt water flux from the Arkona Basin to the Bornholm Basin is minor.

  • 12.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Kauker, F
    Modeling decadal variability of the Baltic Sea: 2. Role of freshwater inflow and large-scale atmospheric circulation for salinity2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no C11, article id 3368Article in journal (Refereed)
    Abstract [en]

    Hindcast simulations for the period 1902 - 1998 have been performed using a three-dimensional coupled ice-ocean model for the Baltic Sea. Daily sea level observations in Kattegat, monthly basin-wide discharge data, and reconstructed atmospheric surface data have been used to force the Baltic Sea model. The reconstruction utilizes a statistical model to calculate daily sea level pressure and monthly surface air temperature, dew point temperature, precipitation, and cloud cover fields. Sensitivity experiments have been performed to explore the impact of the freshwater and saltwater inflow variability on the salinity of the Baltic Sea. The decadal variability of the average salinity is explained partly by decadal volume variations of the accumulated freshwater inflow from river runoff and net precipitation and partly by decadal variations of the large-scale sea level pressure over Scandinavia. During the last century two exceptionally long stagnation periods are found, the 1920s to 1930s and the 1980s to 1990s. During these periods, precipitation, runoff, and westerly winds were stronger, and salt transports into the Baltic were smaller than normal. As the response timescale on freshwater forcing of the Baltic Sea is about 35 years, seasonal and year-to-year changes of the freshwater inflow are too short to affect the average salinity significantly. We found that the impact of river regulation, which changes the discharge seasonality, is negligible.

  • 13. Nikolopoulos, A
    et al.
    Borenäs, Karin
    SMHI, Core Services.
    Hietala, R
    Lundberg, P
    Hydraulic estimates of Denmark Strait overflow2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no C3, article id 3095Article in journal (Refereed)
    Abstract [en]

    Upper bounds of the Denmark Strait deep-water overflow from the Nordic seas into the North Atlantic are estimated using rotating hydraulic theory. The calculations are made for the real bottom topography of the strait and are based on hydrographic sections surveyed during a dedicated field experiment in the area. Results are presented for zero as well as finite (but constant) potential vorticity, and it is shown that the differences in outcome between these two approaches are only minor. The calculated interface configurations are found to be in good agreement with those observed, and the theoretically obtained transports conform with earlier estimates.

  • 14.
    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.

  • 15.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Chen, D L
    Influence of atmospheric circulation on the maximum ice extent in the Baltic Sea2001In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 106, no C3, p. 4493-4500Article in journal (Refereed)
    Abstract [en]

    This work analyzes long-term changes in the annual maximum ice extent in the Baltic Sea and Skagerrak between 1720 and 1997. It focuses on the sensitivity of the ice extent to changes in air temperature and on the relationships between the ice extent and large-scale atmospheric circulation. A significant regime shift in 1877 explains the decreasing trend in the ice extent. The regime shift indicates a change from a relatively cold climate regime to a relatively warm one, which is likely a result of changed atmospheric circulation. In addition, the analysis shows that a colder climate is associated with higher variability in the ice extent and with higher sensitivity of the ice extent to changes in winter air temperature. Moreover, the ice extent is fairly well correlated with the North Atlantic Oscillation (NAO) index during winter, which supports the results of earlier studies. However, the moving correlation analysis shows that the relationship between the NAO index and the ice extent is not stationary over time. A statistical model was established that links the ice extent and a set of circulation indices. It not only confirms the importance of the zonal how but also implies the impact of meridional wind and vorticity. The usefulness of the statistical model is demonstrated by comparing its performance with that of a numerical model and with independent observations. The statistical model achieves a skill close to that of the numerical model. We conclude that this model can be a useful tool in estimating the mean conditions of the ice extent from monthly pressures, allowing for the use of the general circulation model output for predictions of mean ice extent.

  • 16.
    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.

  • 17.
    Rutgersson, Anna
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Smedman, A S
    Hogstrom, U
    Use of conventional stability parameters during swell2001In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 106, no C11, p. 27117-27134Article in journal (Refereed)
    Abstract [en]

    The situation with swell is of climatological importance over the Baltic Sea since swell is present during as much as 40% of the time. In this study, two periods with unstable and two periods with stable stratification and wind following swell are investigated. Data are taken at a small flat island in the Baltic Sea. During unstable stratification the turbulent structure shows great resemblance to the free convective boundary layer and scales with the boundary layer height. Since surface heat flux is too small to support the high levels of turbulence present, inactive turbulence is probably the dominating source. For the stably stratified layer, there are smaller differences between data with and without swell. The turbulence is mainly transported upward into the atmosphere with the aid of pressure fluctuations induced by the waves. For most of the data with swell the gradients are smaller than for growing sea. During unstable conditions the wind gradients are negative, indicating the presence of a wave-driven wind. The gradients increase with increasing height above the surface. The drag coefficient is smaller than is usually found for both stable and unstable stratification and varies very little with wind and stratification. There are only small variations in the heat transfer coefficients with changing stratification, but they are significantly different for stable and unstable stratification.

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