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  • 301.
    Ljungman, Olof
    et al.
    SMHI, Research Department, Oceanography.
    Rydberg, Lars
    SMHI, Research Department, Oceanography.
    Goransson, C G
    Modeling and observations of deep water renewal and entrainment in a Swedish sill fjord2001In: Journal of Physical Oceanography, ISSN 0022-3670, E-ISSN 1520-0485, Vol. 31, no 12, p. 3401-3420Article in journal (Refereed)
    Abstract [en]

    A baroclinically forced deep-water renewal event in a small Swedish sill fjord is investigated using a one-dimensional numerical model and a dataset that resolves temporal variations in salinity and oxygen. The observations indicate an almost complete renewal of the basin water within a period of 2-3 weeks. The details of the renewal process are emphasized by modeling the sill flow as well as the resulting dense bottom plume, with various rates of entrainment. It is found that sill mixing is relatively unimportant, but that entrainment increases the deep-water inflow by a factor of 2-4. Different formulas for calculating plume entrainment are compared and the model's sensitivity to variations in sill flow and bottom friction is investigated. It is shown that even weak entrainment, occurring at shallow depths where the density difference between the plume and the resident water is large, has a significant impact. Entrainment prolongs the time it takes for a complete renewal (i.e., to flush out all resident water) and, on the moderate timescales considered here, yields lower post-renewal salinity and oxygen concentrations. This implies that entrainment (and mixing) during renewal may be as important as basin water diffusion in setting the timescale for forthcoming renewal events.

  • 302. Haapala, J
    et al.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Rinne, J
    Numerical investigations of future ice conditions in the Baltic Sea2001In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 30, no 4-5, p. 237-244Article in journal (Refereed)
    Abstract [en]

    Global climate change is expected to have an effect on the physical and ecological characteristics of the Baltic Sea. Estimates of future climate on the regional scale can be obtained by using either statistical or dynamical downscaling methods of global AOGCM scenario results. In this paper, we use 2 different coupled ice-ocean models of the Baltic Sea to simulate present and future ice conditions around 100 years from present. Two 10-year time slice experiments have been performed using the results of atmospheric climate model simulations as forcing, one representing pre-industrial climate conditions (control simulation), and the other global warming with a 150% increase in CO2 greenhouse gas concentration (scenario simulation). Present-day climatological ice conditions and interannual variability are realistically reproduced by the models. The simulated range of the maximum annual ice extent in the Baltic in both models together is 180 to 420.10(3) km(2) in the control simulation and 45 to 270.10(3) km(2) in the scenario simulation. The range of the maximum annual ice thickness is from 32 to 96 cm and from 11 to 60 cm in the control and scenario simulations, respectively. In contrast to earlier estimates, sea ice is still formed every winter in the Northern Bothnian Bay and in the most Eastern parts of the Gulf of Finland. Overall, the simulated changes of quantities such as ice extent and ice thickness, as well as their interannual variations are relatively similar in both models, which is remarkable, because the 2 coupled ice-ocean model systems have been. developed independently. This increases the reliability of future projections of ice conditions in the Baltic Sea.

  • 303.
    Axell, Lars
    et al.
    SMHI, Research Department, Oceanography.
    Ljungman, Olof
    SMHI, Research Department, Oceanography.
    A One-Equation Turbulence Model for Geophysical Applications: Comparison with Data and the k - epsilon Model2001In: Environmental Fluid Mechanics, ISSN 1567-7419, E-ISSN 1573-1510, Vol. 1, no 1, p. 71-106Article in journal (Refereed)
    Abstract [en]

    A one-equation turbulence model is presented, in which the turbulent kinetic energy k is calculated with a transport equation whereas the turbulent length scale l is calculated with an algebraic expression. The value of l depends on the local stratification and reduces to the classical kappa vertical bar z vertical bar scaling for unstratified flows near a wall, where vertical bar z vertical bar is the distance to the wall. The length scale decreases during stable stratification, and increases for unstable stratification compared to the neutral case. In the limit of strong stable stratification, the so-called buoyancy length scale proportional to k(1/2)N(-1) is obtained, where N is the buoyancy frequency. The length scale formulation introduces a single model parameter which is calibrated against experimental data. The model is verified extensively against laboratory measurements and oceanic data, and comparisons are made with the two-equation k-epsilon model. It is shown that the performance of the proposed k model is almost identical to that of the k-epsilon model. In addition, the stability functions of Launder are revisited and adjusted to obtain better agreement with recent data.

  • 304.
    Pers, Charlotta
    et al.
    SMHI, Research Department, Hydrology.
    Rahm, Lars
    SMHI, Research Department, Oceanography.
    Jonsson, A
    Bergstrom, A K
    Jansson, M
    Modelling dissolved organic carbon turnover in humic Lake Ortrasket, Sweden2001In: Environmental Modelling and Assessment, ISSN 1420-2026, E-ISSN 1573-2967, Vol. 6, no 3, p. 159-172Article in journal (Refereed)
    Abstract [en]

    The organic carbon balance of a lake with high input of allochthonous organic carbon is modelled integrating physical, chemical and biological processes. The physical model captures the behaviour of real thermal stratification in the lake for different flow situations during the period 1993-1997. The dissolved organic carbon model is based on simulated trajectories of water parcels. By tracking parcels, account is kept of environmental factors such as temperature and radiation as well as DOC quality for each parcel, The DOC concentration shows seasonal variations primarily dependent on inflow. The organic matter degradation (bacterial- and photodegradation) in the lake amounts to 1.5-2.5 mg C l(-1) yr(-1), where photooxidation is responsible for approximately 10%. The estimated DIC production in the lake is large compared to sediment mineralisation and primary production. The main conclusion is that the model with the selected parameterisations of the degradation processes reasonably well describes the DOC dynamics in a forest lake.

  • 305. Winsor, P
    et al.
    Rodhe, J
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Baltic Sea ocean climate: an analysis of 100 yr of hydrographic data with focus on the freshwater budget2001In: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 18, no 1-2, p. 5-15Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea climate is analysed based upon long-term oceanographic measurements. The objective of the work is to study the natural variability of present day climate with focus on the freshwater budget. The results are designed to be used for validation of climate models and for discrimination of the significance of modelled climate change scenarios. Almost 100 yr of observations are used in the study, including data for river runoff, water exchange through the Danish Straits (as calculated from river runoff and from sea level data from the Kattegat), salinity data from the Baltic Sea and the Kattegat, and oxygen content in the deep Baltic Sea. The analyses illustrate that freshwater supply to the Baltic shows large variations on time scales up to several decades. The long-term variations in freshwater storage are closely correlated to accumulated changes in river runoff. This indicates strong positive feedback between the amount of outflowing surface water from the Baltic Sea and the salinity of the inflowing Kattegat water. One implication of the study is that climate control simulations must cover several decades, probably up to 100 yr in order to capture the natural variability of present day climate. Also, models designed to study climate change for the Baltic Sea probably need to start integrating from the present day.

  • 306.
    Rutgersson, Anna
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Smedman, A S
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Measured and simulated latent and sensible heat fluxes at two marine sites in the Baltic Sea2001In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 99, no 1, p. 53-84Article in journal (Refereed)
    Abstract [en]

    In this study, turbulent heat flux data from two sites within the Baltic Sea are compared with estimates from two models. The main focus is on the latent heat flux. The measuring sites are located on small islands close to the islands of Bornholm and Gotland. Both sites have a wide wind direction sector with undisturbed over-water fetch. Mean parameters and direct fluxes were measured on masts during May to December 1998. The two models used in this study are the regional-scale atmospheric model HIRLAM and the ocean model PROBE-Baltic. It is shown that both models overestimate the sensible and latent heat fluxes. The overestimation can, to a large extent, be explained by errors in the air-water temperature and humidity differences. From comparing observed and modelled data, the estimated 8-month mean errors in temperature and humidity are up to 1 degreesC and 1 g kg(-1),respectively. The mean errors in the sensible and latent heat fluxes for the same period are approximately 15 and 30 W m(-2), respectively. Bulk transfer coefficients used for calculating heat and humidity fluxes at the surface were shown to agree rather well with the measurements, at least for the unstable data. For stable stratification, the scatter in data is generally large, and it appears that the bulk formulation chosen overestimates turbulent heat fluxes.

  • 307.
    Rutgersson, Anna
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Bumke, K
    Clemens, M
    Foltescu, Valentin
    SMHI.
    Lindau, R
    Michelson, Daniel
    SMHI, Core Services.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Precipitation estimates over the Baltic Sea: Present state of the art2001In: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 32, no 4-5, p. 285-314Article in journal (Refereed)
    Abstract [en]

    Precipitation is one of the main components in the water balance, and probably the component determined with the greatest uncertainties. In the present paper we focus on precipitation (mainly rain) over the Baltic Sea as a part of the BAL-TEX project to examine the present state of the art concerning different precipitation estimates over that area. Several methods are used, with the focus on 1) interpolation of available synoptic stations; 2) a mesoscale analysis system including synoptic, automatic, and climate stations, as well as weather radar and an atmospheric model; and 3) measurements performed on ships. The investigated time scales are monthly and yearly and also some long-term considerations are discussed. The comparison shows that the differences between most of the estimates, when averaged over an extended period and a larger area, are in the order of 10-20%, which is in the same range as the correction of the synoptic gauge measurements due to wind and evaporation losses. In all data sets using gauge data it is important to include corrections for high winds. To improve the structure of precipitation over sea more focus is to be put on the use of radar data and combinations of radar data and other data. Interpolation methods that do not consider orographic effects must treat areas with large horizontal precipitation gradients with care. Due to the large variability in precipitation in time and space, it is important to use long time periods for climate estimates of precipitation. Ship measurements are a valuable contribution to precipitation information over sea, especially for seasonal and annual time scales.

  • 308.
    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.

  • 309. Raschke, E
    et al.
    Meywerk, J
    Warrach, K
    Andrae, Ulf
    SMHI, Research Department, Meteorology.
    Bergström, Sten
    SMHI, Research Department, Hydrology.
    Beyrich, F
    Bosveld, F
    Bumke, K
    Fortelius, C
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    Gryning, S E
    Halldin, S
    Hasse, L
    Heikinheimo, M
    Isemer, H J
    Jacob, D
    SMHI.
    Jauja, I
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    Keevallik, S
    Koistinen, J
    van Lammeren, A
    Lass, U
    Launianen, J
    Lehmann, A
    Liljebladh, B
    Lobmeyr, M
    Matthaus, W
    Mengelkamp, T
    Michelson, Daniel
    SMHI, Core Services.
    Napiorkowski, J
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Piechura, J
    Rockel, B
    Rubel, F
    Ruprecht, E
    Smedman, A S
    Stigebrandt, A
    The Baltic Sea Experiment (BALTEX): A European contribution to the investigation of the energy and water cycle over a large drainage basin2001In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 82, no 11, p. 2389-2413Article, review/survey (Refereed)
    Abstract [en]

    The Baltic Sea Experiment (BALTEX) is one of the five continental-scale experiments of the Global Energy and Water Cycle Experiment (GEWEX). More than 50 research groups from 14 European countries are participating in this project to measure and model the energy and water cycle over the large drainage basin of the Baltic Sea in northern Europe. BALTEX aims to provide a better understanding of the processes of the climate system and to improve and to validate the water cycle in regional numerical models for weather forecasting and climate studies. A major effort is undertaken to couple interactively the atmosphere with the vegetated continental surfaces and the Baltic Sea including its sea ice. The intensive observational and modeling phase BRIDGE, which is a contribution to the Coordinated Enhanced Observing Period of GEWEX, will provide enhanced datasets for the period October 1999-February 2002 to validate numerical models and satellite products. Major achievements have been obtained in an improved understanding of related exchange processes. For the first time an interactive atmosphere-ocean-land surface model for the Baltic Sea was tested. This paper reports on major activities and some results.

  • 310.
    Rummukainen, Markku
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Räisänen, Jouni
    SMHI, Research Department, Climate research - Rossby Centre.
    Bringfelt, Björn
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    A regional climate model for northern Europe: model description and results from the downscaling of two GCM control simulations2001In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 17, no 5-6, p. 339-359Article in journal (Refereed)
    Abstract [en]

    This work presents a regional climate model, the Rossby Centre regional Atmospheric model(RCA1), recently developed from the High Resolution Limited Area Model (HIRLAM). The changes in the HIRLAM parametrizations, necessary for climate-length integrations, are described. A regional Baltic Sea ocean model and a modeling system for the Nordic inland lake systems have been coupled with RCA1. The coupled system has been used to downscale 10-year time slices from two different general circulation model (GCM) simulations to provide high-resolution regional interpretation of large-scale modeling. A selection of the results from the control runs, i.e. the present-day climate simulations, are presented: large-scale free atmospheric fields, the surface temperature and precipitation results and results for the on-line simulated regional ocean and lake surface climates. The regional model modifies the surface climate description compared to the GCM simulations, but it is also substantially affected by the biases in the GCM simulations. The regional model also improves the representation of the regional ocean and the inland lakes, compared to the GCM results.

  • 311.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    The use of the k – e turbulence model within the Rossby Centre regional ocean climate model: parameterization development and results2000Report (Other academic)
  • 312.
    Marmefelt, Eleonor
    et al.
    SMHI, Professional Services.
    Håkansson, Bertil
    SMHI, Research Department, Oceanography.
    Erichsen, Anders Christan
    Sehested Hansen, Ian
    Institute of Marine Research, Bergen, Norway..
    Development of an Ecological Model System for the Kattegat and the Southern Baltic: Final Report to the Nordic Councils of Ministers2000Report (Other academic)
  • 313.
    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.

  • 314. Hajdu, S
    et al.
    Edler, Lars
    SMHI, Research Department, Oceanography.
    Olenina, I
    Witek, B
    Spreading and establishment of the potentially toxic dinoflagellate Prorocentrum minimum in the Baltic Sea2000In: International review of hydrobiology, ISSN 1434-2944, E-ISSN 1522-2632, Vol. 85, no 5-6, p. 561-575Article in journal (Refereed)
    Abstract [en]

    During the last two decades the potentially toxic dinoflagellate Prorocentrum minimum (PAVILLARD) SCHILLER has successfully established itself in the Baltic Sea. It is now a dominant summer species in the southern Baltic proper, and reaches as far into the low salinity of the northern Baltic as the central Gulf of Finland. In the 1990s, it developed several coastal blooms in the eastern and northern Baltic proper, but occurred irregularly between years. Field data show that P. minimum can grow at salinities below 5 PSU, confirming its potential to penetrate farther into the low saline part of the Baltic Sea. Biometric data show that P. minimum cells differ significantly in size between areas in the Baltic Sea.

  • 315.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Rutgersson, Anna
    SMHI, Research Department, Climate research - Rossby Centre.
    Closing the water and heat cycles of the Baltic Sea2000In: Meteorologische Zeitschrift, ISSN 0941-2948, E-ISSN 1610-1227, Vol. 9, no 1, p. 59-66Article in journal (Refereed)
    Abstract [en]

    The objective of the present paper is to analyze the water and heat cycles of the Baltic Sea. The closure equations fur the water and heat cycles are formulated and the appropriate fluxes are calculated using the ocean model PROBE-Baltic forced by meteorological fields, river runoff and sea level data from the Kattegat. The time period considered is from November 1980 to November 1995. In the closing of the water cycle it is clear that river runoff, net precipitation (precipitation minus evaporation), in- and outflows through the Baltic Sea entrance area are the dominating flows. From the ocean model it is illustrated that the long-term water balance is consistent with the salinity in the Baltic Sea and that the net precipitation is positive during the studied period. For the closing of the heat cycle, the net heat loss to the atmosphere from the open water surface, as an annual moan, is in close balance with the solar radiation. The dominating fluxes in the net heat loss to the atmosphere are the sensible heat flux, the latent heat Aux and the net long wave radiation. The heat flux from water to ice also needs to be included in the modeling efforts. Heat flows associated with precipitation in the form of rain and snow can, as annual means, be neglected as well as the heat fluxes associated with river runoff, solar radiation through the ice and ice advecting out through the Baltic Sea entrance area. The total annual mean heat loss from the water body is in close balance with the annual change of heat storage in the water and the net heat exchange through the Baltic Sea entrance area is small. This illustrates that the Baltic Sea thermodynamically responds as a closed ocean basin.

  • 316.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Gustafsson, B
    Rodhe, J
    Walin, G
    Use of Baltic Sea modelling to investigate the water cycle and the heat balance in GCM and regional climate models2000In: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 15, no 2, p. 95-108Article in journal (Refereed)
    Abstract [en]

    Results from the first simulations with the Rossby Centre regional climate atmosphere (RCA) model were used to force 2 versions of process-oriented models of the Baltic Sea-one time-dependent, the other considering the mean state. The purpose was primarily to obtain a first scenario of the future state of the Baltic Sea. In addition, we looked at this exercise as a method to evaluate the consistency of the water cycle and the heat balance produced by atmospheric climate models. The RCA model is a high-resolution atmospheric regional model which is forced with lateral conditions from a global model. A large-scale Baltic drainage basin hydrological model, forced by the RCA model, was used to simulate river runoff. Using RCA model data from the control run we found that that the temperature and ice conditions in the Baltic Sea were reasonably realistic while the salinity field was poorly reproduced. We conclude that the modelling of the water cycle needs considerable improvement. We also conclude that the time for the Baltic Sea to respond to the water cycle is much longer than the integration period so far used with the RCA model. Forcing the ocean models with RCA model data from a future scenario with an enhanced greenhouse effect gives an increased sea-surface temperature and a much reduced extent of ice in the Baltic Sea due to climate warming. Also the salinity is reduced, which implies possible serious effects on the future marine life in the Baltic Sea. The results demonstrate that accurate atmospheric modelling of not only the heat balance but also the water cycle is crucial for Baltic Sea climate simulations.

  • 317.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    First results of multi-year simulations using a 3D Baltic Sea model1999Report (Other academic)
  • 318.
    Meier, Markus
    et al.
    SMHI, Research Department, Oceanography.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Coward, Andrew C.
    James Renell Div,. Southhampton Oceanogr. Centre.
    Nycander, Jonas
    MISU.
    Döös, Kristofer
    MISU.
    RCO – Rossby Centre regional Ocean climate model: model description (version 1.0) and first results from the hindcast period 1992/931999Report (Other academic)
    Abstract [en]

    Within SWECLIM a 3D fully coupled ice-ocean model has been developed based on the massively parallel OCCAM code from Southampton. Compared to the global OCCAM the model has to be adopted to Baltic Sea conditions with implementations of high-frequent atmospheric forcing fields in connection with adequate bulk formulae for wind stress, heat uxes and freshwater uxes, solar radiation, river runoff, active open boundary conditions, a second-order moment turbulence closure scheme and a dynamic-thermodynamic sea ice model. Thereby, state-of-the-art sub-models and parameterizations have been used. RCO is the first 3D coupled ice-ocean model for the Baltic Sea with the above mentioned specifications suitable for use on mpp computers like CRAY-T3E's. Thus, a milestone for 3D ocean model development has been set. No other model is as fast as RCO. The performance has been improved significantly using advanced algorithms to optimize processor maps. This guarantees work load balance between the different processors. From now on it is possible to perform longterm simulations (10 years) within SWECLIM using a sufficiently resolved 3D Baltic Sea model. The open boundary conditions have been tested. They allow waves to radiate out of the model domain and signals prescribed at the border to in uence the model interior. No significant trends (like emptying or filling) have been observed which might prevent longer integrations of the system. An option has been included in RCO for active open boundary conditions also for temperature and salinity. For the first time the turbulence closure model has been tested within a 3D model in all Baltic sub-basins. The new flux boundary conditions for turbulent kinetic energy parameterizing breaking surface waves perform well. First results for the hindcast period 1992/93 are presented. Therefor, realistic atmospheric, runoff and boundary data have been used. The model is initialized using observed profile temperature and salinity data. A spin-up period of 3 months starting in May is sufficient to smooth out artificial gradients from the initialization procedure and to turn in basin wide volume changes correctly. The model results have been compared to sea level, sea surface temperature, temperature/salinity profile and ice thickness/compactness data with good agreement. Basin wide volume changes as well as daily sea level oscillations are simulated surprisingly good. Sea surface temperatures follow the observed seasonal cycle. Up- and downwelling events in RCO occur as observed with the right frequency and area extent but the sst's tend to be colder in upwelling and warmer in downwelling regions compared to observations. Mixed layer depths, which are important for the ocean heat content, agree well with previous model studies which are validated against observations intensively (Meier, 1996). The water exchange between Baltic and North Sea crucial for multi-year integrations is modelled realistically. Especially the salt water inflow in January 1993 can be reproduced. The bottom water in Bornholm Basin is replaced by new water originating from the North Sea but maximum observed bottom salinities at Bornholm Deep are underestimated by 1-2 PSU. Freezing, breakup date and maximum ice extent are in good correspondence with observations. Improved parameterizations result in modelled ice thicknesses as observed whereas other authors report too large ice thicknesses and delayed ice melting (e.g., Haapala and Lepparanta,1996). Multi-year simulations including mild, normal and severe winters will be necessary to elucidate this problem further. A comparison between an experiment with full dynamic-thermodynamics and one without dynamic effects reveals the importance of ice advection under wind influence. A process study from the beginning of February 1993 showed that under strong wind conditions a hole in the ice coverage can open with the size of half of the Bothnian Bay. At the end of January 1993 the Bothnian Bay, the coastal area of the Bothnian Sea and the eastern parts of the Gulf of Finland are ice covered. A couple of days later westerly winds led to wide open areas in the western Bothnian Bay while ice piled up at the eastern coasts to a correct amount. This phenomenon can be modelled only with ice dynamics included. The aim of SWECLIM is to increase our knowledge of the effects of climate change in Sweden and the other Nordic countries. Therefor, it is necessary to understand the present climate. For the Baltic Sea even the knowledge about the present mean state and its transients is rather poor. Only a small number of long-time observations like sea level records (for example from Stockholm, see Ekman (1988)), maximum annual ice extent (e.g., Palosuo, 1953; Seina and Palosuo, 1993) or temperature and salinityprofiles from monitoring stations in some of the sub-basins (e.g., Matthaus and Frank,1992) are available. These informations are not enough to understand the driving mechanisms of mean horizontal and vertical transports of energy, momentum and matter. 3D Baltic Sea models like RCO will close this knowledge gap in future. Thereby, it will be possible to close the water and energy cycle of the Baltic catchment area, a final goal of BALTEX. By applying atmospheric forcing data from scenario simulations in one- or two-way coupled mode it will be possible to make predictions of climate change for the Baltic Sea. Impact studies of the future marine environment will be available using detailed highly resolved information from RCO. This report presents a powerful tool for solving these and other tasks.

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  • 319.
    Persson, Tomas
    SMHI, Research Department, Oceanography.
    Solar radiation climate in Sweden1999In: Physics and chemistry of the earth. Part B: Hydrology, oceans and atmosphere, ISSN 1464-1909, E-ISSN 1873-4677, Vol. 24, no 3, p. 275-279Article in journal (Refereed)
    Abstract [en]

    Since 1983 a Swedish network of 12 solar radiation stations, measuring global radiation, G, and direct normal irradiance, EN, is Operated by SMHI. All stations are sited within the BALTEX area. During the fifteen years 1983-1997, for which a homogeneous radiation database has been built up, some clear features in the radiation climate show up. The largest difference in G on annular basis is between the stations Visby, located on the island of Gotland in the Baltic Sea, and Kiruna, the northernmost station. The mean annual total of G in Kiruna (2822 MJm(-2)) is 25 % less than in Visby (3758 MJm(-2)). This is due to both latitudinal effects and differing cloud conditions. The effect of different cloudiness is clearly seen when comparing the stations Vaxjo and Visby, which are only separated by 0.74 degrees in latitude. At the cloudier site in Vaixjo, G is on the average 12 % less than in Visby. At all stations there is a large year to year variation of 15 %, or more. During the period analysed there is a clear increasing trend in both G, EN and duration of bright sunshine at all stations. The trend in G averaged over all stations is + 7.2 %/decade. This is mainly caused by decreasing cloudiness, especially during the summer months. Taking the atmospheric water vapour into account, the (A) over circle ngstrom turbidity coefficient, beta, have been estimated from the measurements of EN Mean values of beta during 1983-1997 are 0.082 in Lund (station with highest turbidity) and 0.056 in Kiruna (station with lowest turbidity). These values are strongly affected, approximately to the same extent, by the major volcanic eruptions of El Chichon and Mt. Pinatubo. (C) 1999 Elsevier Science Ltd. All rights reserved.

  • 320.
    Brandt, Maja
    et al.
    SMHI, Core Services.
    Edler, Lars
    SMHI, Research Department, Oceanography.
    Andersson, Lars
    SMHI, Core Services.
    Översvämningar längs Oder och Wisla sommaren 1997 samt effekterna i Östersjön1998Report (Other academic)
    Abstract [sv]

    I juli drabbades Tjeckien och Polen av mycket intensiva regnväder. Det första kom 4-9/7 och det andra inträffade 18-21/7. Över floderna Oder och Wislas avrinningsområden föll 3-4 gånger så mycket nederbörd som normalt. Utifrån vattenföringuppgifterna beräknades, att det under perioden 11/7-31/8 hade runnit ut 17 km3 från dessa floder till Östersjön. Den normala avrinningen från Oder och Wisla är under denna tidsperiod ca 6 km3, vilket innebär ett överskott på ca 11 km3• Det kan jämföras med en veckas inflöde genom Öresund, som är av storleksordningen 10 km3.

    De stora regnmängderna medförde, att stora områden översvämmades främst längs Oder och att flodvattnet förde med sig material och föroreningar längs vattendragen. De svenska hydrografiska basundersökningarna i södra Östersjön intensifierades för att undersöka flodvattnets spridning och materialtransport i södra Östersjön. Undersökningarna utfördes till största delen av SMHI, och i ett nära samarbete med Naturvårdsverket, Fiskeriverket, IVL och Kustbevakningen. Tyska och polska fartyg utförde även intensiva mätningar under den aktuella tiden.

    Flodvattnets väg ut i Östersjön prognostiserades och följdes på ett antal olika sätt. Vinduppgifter, den oceanografiska modellen HIROMB samt spridningsmodell för olja och kemikalier användes för att prognostisera vattnets väg samtidigt som översvämningsvattnet följdes med hjälp av satellitbilder och fartygsmätningar.

    Wisla rinner ut i Gdanskbukten, medan Oder rinner ut i Pommerska bukten efter att ha passerat Szczecin-lagunen. De uppmätta närsaltkoncentrationerna i bukterna var i samma storleksordning som de maximala halter som uppmätts under vårperioderna de senaste 25 åren. Det näringsrika vattnet orsakade en kraftig primärproduktion i bukterna. I slutet av juli rådde västliga vindar, som transporterade det utströmmande vattnet från Wisla och Oder österut längs den polska kusten. I början av augusti vände vinden och blev ostlig. Vädret var varmt och soligt, och vattnet transporterade långsamt västerut. Någon påverkan längre ut från kusten registrerades inte och några långtidseffekter förväntas inte heller ske.

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