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  • 1201.
    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.

  • 1202.
    Arheimer, Berit
    et al.
    SMHI, Research Department, Hydrology.
    Lidén, R.
    SMHI.
    Nitrogen and phosphorus concentrations from agricultural catchments - influence of spatial and temporal variables2000In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 227, no 1-4, p. 140-159Article in journal (Refereed)
    Abstract [en]

    The eutrophication problem has drawn attention to nutrient leaching from arable land in southern Sweden, and further understanding of spatial and temporal variability is needed in order to develop decision-making tools. Thus, the influence of spatial and temporal variables was analysed statistically using empirical time series of different nutrient species from 35 well-documented catchments (2-35 km(2)), which have been monitored for an average of 5 years. In the spatial analysis several significant correlations between winter median concentrations and catchment characteristics were found. The strongest correlation was found between inorganic nitrogen and land use, while concentrations of different phosphorus species were highly correlated to soil texture. Multiple linear regression models gave satisfactory results for prediction of median winter concentrations in unmeasured catchments, especially for inorganic nitrogen and phosphate. In the analysis of temporal variability within catchments, internal variables from a dynamic hydrological model (HBV) were linked to concentration fluxes. It was found that phosphorus and inorganic nitrogen concentrations were elevated during flow increase at low-Bow conditions, while they were diluted as the wetness in the catchment increased. During unmonitored periods regression models were successful in predicting temporal variability of total phosphorus, phosphate and inorganic nitrogen, while organic nitrogen and particulate phosphorus could not be predicted with this approach. Dividing the data into different flow categories did not improve the prediction of nutrient concentration dynamics. The results and literature review presented, confirm parts of the present HBV-W model approach and will be useful for further development of nutrient routines linked to dynamic hydrological models. (C) 2000 Elsevier Science B.V. All rights reserved.

  • 1203. 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.

  • 1204.
    Graham, Phil
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Jacob, D
    Using large-scale hydrologic modeling to review runoff generation processes in GCM climate models2000In: Meteorologische Zeitschrift, ISSN 0941-2948, E-ISSN 1610-1227, Vol. 9, no 1, p. 49-57Article in journal (Refereed)
    Abstract [en]

    A large-scale application of the Swedish HBV hydrologic model was used to model the daily water balance of total runoff to the Baltic Sea. Ten-year present atmospheric climate model simulations from the ECHAM4/T106 global climate model were summarized on a runoff catchment basis. Climate model daily temperature and precipitation for the Baltic region were input to the water balance model for intercomparison runs. Comparison of results from the water balance model - with climate model input - to direct results from the climate model provides critical review of the behavior of the climate model. This: helped pinpoint systematic compensating errors in the land parameterization scheme.

  • 1205.
    Foltescu, Valentin
    SMHI.
    Prediction of crop yield in Sweden based on mesoscale meteorological analysis2000In: Meteorological Applications, ISSN 1350-4827, E-ISSN 1469-8080, Vol. 7, no 4, p. 313-321Article in journal (Refereed)
    Abstract [en]

    This paper presents a prediction system for regional crop growth in Sweden, recently set up at SMHI (Swedish Meteorological and Hydrological Institute). The system includes a state-of-the-art crop growth model, WOFOST (WOrld FOod STudies) and inputs from meteorological mesoscale analysis. The simulated crops dye spring barley, spring rape, oats and winter wheat, and the period of investigation is 1985-98. The simulated water-limited grain yield is used as a predictor in the yield prediction procedure. The technological time trend describing the yearly increase of the production level is accounted for as well. Yield prediction based on crop growth modelling is justified since the ability to forecast the yield is higher compared to that using the technological time trend alone. The prediction errors are of the order of 8 to 16%, with the lowest errors for winter wheat and spring barley.

  • 1206. van den Dool, H M
    et al.
    Saha, S
    Johansson, Åke
    SMHI, Research Department, Meteorology.
    Empirical orthogonal teleconnections2000In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 13, no 8, p. 1421-1435Article in journal (Refereed)
    Abstract [en]

    A new variant is proposed for calculating functions empirically and orthogonally from a given space-time dataset. The method is rooted in multiple linear regression and yields solutions that are orthogonal in one direction, either space or time. In normal setup, one searches for that point in space, the base point (predictor). which, by linear regression, explains the most of the variance at all other points (predictands) combined. The first spatial pattern is the regression coefficient between the base point and all other points, and the first time series is taken to be the time series of the raw data at the base point. The original dataset is next reduced; that is, what has been accounted for by the first mode is subtracted out. The procedure is repeated exactly as before for the second, third, etc., modes. These new functions are named empirical orthogonal teleconnections (EOTs). This is to emphasize the similarity of EOT to both teleconnections and (biorthogonal) empirical orthogonal functions (EOFs). One has to choose the orthogonal direction for EOT. In the above description of the normal space-time setup, picking successive base points in space, the time series are orthogonal. One can reverse the role of time and space-in this case one picks base points in time, and the spatial maps will be orthogonal. If the dataset contains biorthogonal modes, the EOTs are the same for both setups and are equal to the EOFs. When applied to four commonly used datasets, the procedure was found to work well in terms of explained variance (EV) and in terms of extracting familiar patterns. In all examples the EV for EOTs was only slightly less than the optimum obtained by EOF. A numerical recipe was given to calculate EOF, starting from EOT as an initial guess. When subjected to cross validation the EOTs seem to fare well in terms of explained variance on independent data las good as EOF). The EOT procedure can be implemented very easily and has, for some (but not all) applications, advantages over EOFs. These novelties, advantages, and applications include the following. 1) One can pick certain modes (or base point) first-the order of the EOTs is free, and there is a near-infinite set of EOTs. 2) EOTs are linked to specific points in space or moments in time. 3) When linked to Row at specific moments in time, the EOT modes have undeniable physical reality. 4) When linked to flow at specific moments in time, EOTs appear to be building blocks for empirical forecast methods because one can naturally access the time derivative. 5) When linked to specific points in space, one has a rational basis to define strategically chosen points such that an analysis of the whole domain would benefit maximally from observations at these locations.

  • 1207.
    Michelson, Daniel
    et al.
    SMHI, Core Services.
    Foltescu, Valentin
    SMHI.
    Häggmark, Lars
    SMHI, Core Services.
    Lindgren, Bo
    SMHI.
    MESAN Mesoscale analysis of precipitation2000In: Meteorologische Zeitschrift, ISSN 0941-2948, E-ISSN 1610-1227, Vol. 9, no 2, p. 85-96Article in journal (Refereed)
    Abstract [en]

    The Mesoscale Analysis System (MESAN) has been running operationally since April, 1997, providing science and consumers of weather information with spatially continuous fields of nine analysed meteorological parameters every hour. Data input to MESAN consists of surface observations from different observation systems, numerical weather prediction model fields, weather radar and satellite imageries, and climate information. Each data source is quality controlled before being subjected to an optimal interpolation (OI) scheme, together with data from the other sources. This paper presents MESAN's accumulated precipitation product. The methods used for interpolation of the multisource data are presented and discussed, as are the methods used to quality control each data source. Results from August-October 1995, using multisource data including gauge observations from the countries in the Baltic Sea Experiment (BALTEX) Region, exemplify the product. OI, used with a variable first guess error, has been compared with conventional inverse distance interpolation of precipitation in two catchments in mountainous terrain. Verification was conducted through modelled runoff, using areally integrated accumulated precipitation, compared with hydrograph observations. Significant improvements using OI were found in one of the catchments. The relative contribution (or importance) of each data source to the analysis has been evaluated using cross validation. Results show that gauge networks are the single most important sources and that radar imagery makes a significant contribution in areas lacking networks of dense gauges, such as the Baltic Sea. Analysis quality improves with the use of a greater number of input data sources. MESAN is an appropriate tool for creating an overall best estimate precipitation analysis and should be useful in applications where such information is required. In validating precipitation produced by numerical weather prediction models. analyses generated without the use of such model fields is recommended.

  • 1208.
    Häggmark, Lars
    et al.
    SMHI, Core Services.
    Ivarsson, Karl-Ivar
    SMHI, Core Services.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    Olofsson, R O
    Mesan, an operational mesoscale analysis system2000In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 52, no 1, p. 2-20Article in journal (Refereed)
    Abstract [en]

    A system for mesoscale analyses of selected variables has been developed. The analysed parameters are of general interest in operational weather forecasting, but normally not available from NWP systems, or available, but with a significantly lower quality than achieved by the mesoscale analysis system. A supplementary objective is to produce initial information to be used for now-casting techniques. Examples of parameters are precipitation, temperature, humidity, visibility, wind and clouds. The basis of the analysis system is the optimal interpolation technique (OI). The use of observations from automatic stations, radars and satellites have been investigated. The investigation indicates that a dense network of ordinary precipitation gauge measurements can produce more accurate analyses than more elaborate systems like radar that suffers from anomalous echoes and other errors.

  • 1209.
    Lindskog, Magnus
    et al.
    SMHI, Research Department, Meteorology.
    Jarvinen, H
    Michelson, Daniel
    SMHI, Core Services.
    Assimilation of radar radial winds in the HIRLAM 3D-Var2000In: Physics and chemistry of the earth. Part B: Hydrology, oceans and atmosphere, ISSN 1464-1909, E-ISSN 1873-4677, Vol. 25, no 10-12, p. 1243-1249Article in journal (Refereed)
    Abstract [en]

    During the last decade several attempts of assimilating radar wind data into atmospheric models have been reported by various research groups. Some of these are briefly reviewed here. A three-dimensional variational data assimilation (3D-Var) scheme for the High Resolution Limited Area Model (HIRLAM) forecasting system has been developed and prepared for assimilation of low elevation angle radar radial wind superobservations. The HIRLAM 3D-Var is based on a minimization of a cost function that consists of one term measuring the distance between the resulting analysis and a background field, which is a short-range forecast, and another term measuring the distance between the analysis and the observations. The development required for assimilating the radial wind data includes software for generating and managing the superobservations from polar volume data, a quality control algorithm and an observation operator for providing the model counterpart of the observation. The functionality of the components have been evaluated through assimilation experiments using data from Finnish and Swedish radars and further studies are underway. (C) 2000 Elsevier Science Ltd. All rights reserved.

  • 1210. Zunckel, M
    et al.
    Robertson, Lennart
    SMHI, Research Department, Air quality.
    Tyson, P D
    Rodhe, H
    Modelled transport and deposition of sulphur over Southern Africa2000In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 34, no 17, p. 2797-2808Article in journal (Refereed)
    Abstract [en]

    Ambient SO2 concentrations and atmospheric deposition of sulphur resulting from emissions on the industrialised highveld region of South Africa are estimated using the multi-scale atmospheric transport and chemistry (MATCH) modelling system, developed at the Swedish Meteorological and Hydrological Institute (SMHI), and compared with an inferential model driven by measured input quantities. Modelled SO, concentrations on the central highveld mostly range between 10 and 50 ppb, exceeding 50 ppb in source areas. Dry deposition rates for sulphur exhibit a similar spatial pattern to the ambient SO2 concentrations and both are consistent with synoptic-scale transport patterns. Maximum dry deposition rates for sulphur of more than 10 kg S ha(-1) a(-1) occur over the central highveld with a well-defined gradient decreasing away from the source region. Despite the significant differences in modelling approaches, the estimates of dry deposition provided by MATCH are in reasonable agreement with those of the inferential model. The maximum modelled wet deposition rates occur over the South African highveld and its periphery and range between 1 and 5 kg S ha(-1) a(-1) and compare favourably with measurements from an acid rain network. Wet deposition generally exceed dry deposition on the highveld and the adjacent areas except in the central highveld source region. Over the drier western half of South Africa MATCH-modelled dry and wet deposition rates are again similar and are less that 1 kg S ha(-1) a(-1). Wet deposition exceeds dry in the higher rainfall regions along the south and east coasts of South Africa. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.

  • 1211. Pechinger, U
    et al.
    Dittmann, E
    Erbes, G
    Johansson, P
    Karppinen, A
    Musson-Genon, L
    Omstedt, Gunnar
    SMHI, Research Department, Air quality.
    Tercier, P
    Intercomparison of methods for parameterizing components of the surface energy balance - a summary of Working Group 1 - COST 710 results2000In: International Journal of Environment and Pollution, ISSN 0957-4352, E-ISSN 1741-5101, Vol. 14, no 1-6, p. 558-564Article in journal (Refereed)
    Abstract [en]

    Working Group 1 of COST Action 710 investigated the use of meteorological pre-processors for short-range dispersion models for regulatory purposes. Two commonly used schemes for estimating boundary-layer fluxes from standard meteorological observations were intercompared using high latitude measurements from Sweden for spring/summer and winter conditions. Ground heat fluxes estimated with five different schemes were compared for data measured in Switzerland. The main results of these studies are presented.

  • 1212.
    Alexandersson, Hans
    et al.
    SMHI.
    Tuomenvirta, H
    Schmith, T
    Iden, K
    Trends of storms in NW Europe derived from an updated pressure data set2000In: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 14, no 1, p. 71-73Article in journal (Refereed)
    Abstract [en]

    Within the WASA project (von Storch et al. 1998; Bull Am Meterol Soc 79(5):741-760) an extensive data set containing station pressure values was used to calculate geostrophic winds (Alexandersson et al. 1998; Global Atmos Ocean Syst 6:97-120). Geostrophic winds were analysed in terms of percentiles to give a measure of long-term variations in synoptic-scale storminess. In this paper an update to 1998 is presented. In the Scandinavia, Finland and Baltic Sea area the most recent years, especially the cold and calm year 1996, seem to have brought an end to the stormy period centred on 1990. In the more westerly British Isles, North Sea and Norwegian Sea area, storminess is still at high levels compared with the less intense period between 1930 and 1980. The long-term increasing trend in NW Europe storminess that started in the 1960s seems to have been broken.

  • 1213.
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    Satellite sensing techniques and applications for the purpose of BALTEX2000In: Meteorologische Zeitschrift, ISSN 0941-2948, E-ISSN 1610-1227, Vol. 9, no 2, p. 111-116Article in journal (Refereed)
    Abstract [en]

    Various satellite sensing techniques and their corresponding applications suitable for use in validation and modelling activities in BALTEX are presented and discussed. Special emphasis is given to data and mature applications available during the main BALTEX BRIDGE experiment. For atmospheric simulations and studies, sensors measuring radiation budget quantities, cloud properties, moisture content and precipitation are considered as most important. Sensors measuring ice conditions and sea state parameters are identified for oceanographical applications and sensors measuring snow conditions and surface conditions are listed for hydrological studies. One example of an application based on extracted cloud information from NOAA AVHRR imagery is demonstrated. Estimations of mean cloud conditions in summer for the period 1991-1998 are shown for the total cloud cover, Cirrus cloudiness and low-level cloudiness over the Nordic region. It is shown that the Baltic Sea and other sea surfaces in the region has a large impact in suppressing summertime cloudiness, in particular low-level cloudiness. As a contrast, cloud patterns for high-level clouds show low correlation with the spatial distribution of sea surfaces. The influence of topographic features (i.e., the Scandinavian mountain range) seems more important here. Cirrus cloudiness peak on the lee side (to the east) of mountains suggesting a frequent presence of lee-wave cirrus clouds. As a summary, the following satellites and sensors will be the main satellite data sources for BALTEX: the ScaRaB instruments on the Ressurs and METEOR satellites, the CERES instrument on the EOS-AMI satellite, the AVHRR and ATOVS sensors on the NOAA satellites. the MVIRI and SEVIRI sensors on the METEOSAT satellites, the SAR instruments on the ERS, Radarsat and ENVISAT satellites and the SSM/I instrument on the DMSP satellites. Of particular interest is also radio occultation measurements of the radio signals from the GPS satellites. The need for a central BALTEX coordination facility (a satellite data function) with the objective to compile and transfer satellite data from various processing centres to BALTEX research groups is particularly stressed.

  • 1214.
    Michelson, Daniel
    et al.
    SMHI, Core Services.
    Koistinen, J
    Gauge-radar network adjustment for the Baltic Sea Experiment2000In: Physics and chemistry of the earth. Part B: Hydrology, oceans and atmosphere, ISSN 1464-1909, E-ISSN 1873-4677, Vol. 25, no 10-12, p. 915-920Article in journal (Refereed)
    Abstract [en]

    The gauge adjustment technique used to produce 2 x 2 km 3- and 12-hour radar-based accumulated precipitation datasets for the Baltic Sea Experiment is presented. The gauge adjustment technique is based on the gauge-to-radar ratio. A distance-dependent adjustment factor is derived and it is weighted against a spatially analyzed adjustment factor according to the local observation density and estimated spatial decorrelation distance. A preliminary adjustment strategy is applied in order to normalize data from many radars to a common level and to minimize the bias with gauges. The final adjustment field applied to radar accumulations is shown, through validation against independent gauge data, to minimize the bias between radar and gauge sums while raising the explained variance, compared to unadjusted radar sums. Areas not covered by radar are subjected to an optimal interpolation of systematically corrected gauge sums, and this field is merged with the gauge adjusted radar field in order to cover the entire Baltic Sea Experiment region. (C) 2000 Elsevier Science Ltd. All rights reserved.

  • 1215.
    Rutgersson, Anna
    SMHI, Research Department, Climate research - Rossby Centre.
    A comparison between long term measured and modeled sensible heat and momentum fluxes using a High Resolution Limited Area Model (HIRLAM)2000In: Meteorologische Zeitschrift, ISSN 0941-2948, E-ISSN 1610-1227, Vol. 9, no 1, p. 31-39Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to study the surface fluxes obtained by a High Resolution Limited Area Model (HIRLAM), used for weather forecasts. The question arises whether the quality of the fluxes are high enough to make HIRLAM a proper tool for performing calculations of the water and energy budgets over the Baltic Sea, which is one of the aims of the BALTEX project. Turbulent fluxes modeled by HIRLAM are compared with direct flux measurements over sea for an extended time period. The model is shown to overestimate both sensible heat and momentum flux for the studied period. The sensible heat Aux for the studied period is overestimated by 8.1 W/m(2) and the momentum flux is systematically overestimated by 0.03 kg/ms(2) or 50 %. It is shown that the values of parameters in the surface parameterization scheme can be improved, for example will a lower value of the Charnock's coefficient agree better with the measurements. The sensitivity of the surface scheme to changes in mean parameters is studied. It is also shown that it is of great importance to have correct values of the near surface wind speed and the temperature difference between air and sea to obtain correct fluxes.

  • 1216. Hansson, M
    et al.
    Michelson, Daniel
    SMHI, Core Services.
    Integration of radar with analysis fields - Bringing distant radar observations "down to Earth"2000In: Physics and chemistry of the earth. Part B: Hydrology, oceans and atmosphere, ISSN 1464-1909, E-ISSN 1873-4677, Vol. 25, no 10-12, p. 1033-1036Article in journal (Refereed)
    Abstract [en]

    Normal refraction of radar waves through the atmosphere prevents radar data at distant ranges from being quantitatively representative for the Earth's surface unless precipitation-related processes taking place between the radar echo and the surface are taken into account. A one-dimensional model is presented which uses a physical description of the processes involved in obtaining surface precipitation rate from a radar echo aloft, comprising local production, coalescence and evaporation. One or two cloud layers are assumed depending on the cloud base height. Input data are operationally analysed cloud base height, temperature, and humidity along with radar observations and their altitudes. At the moment, only precipitation as liquid water is assumed in the model. The method and results using it will be presented and discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.

  • 1217.
    Michelson, Daniel
    et al.
    SMHI, Core Services.
    Liljeberg, B M
    Pilesjo, P
    Comparison of algorithms for classifying Swedish landcover using Landsat TM and ERS-1 SAR data2000In: Remote Sensing of Environment, ISSN 0034-4257, E-ISSN 1879-0704, Vol. 71, no 1, p. 1-15Article in journal (Refereed)
    Abstract [en]

    Sixteen landcover classes in a representative Swedish environment were analyzed and classified using one Landsat TM scene and seven ERS-1 SARPRI images acquired during 1993. Spectral and backscattering signature separabilities are analyzed using the Jeffries-Matusita distance measure to determine which combinations of channels/images contained the most information. Maximum likelihood, sequential maximum a posteriori (SMAP, a Bayesian image segmentation algorithm), and back propagation neural network classification algorithms were applied and their performances evaluated. Results of the separability analyses indicated that the multitemporal SAR data contained more separable landcover information than did the multispectral TM data; the highest separabilities were achieved when the TM and SAR data were combined. Classification accuracy evaluation results indicate that the SMAP algorithm out-performed the maximum likelihood algorithm which, in turn, outperformed the neural network algorithm. The best KAPPA values, using combined data, were 0.495 for SMAP, 0.0445 for maximum likelihood, and 0.432 for neural network. Corresponding overall accuracy values were 57.1%, 52.4%, and 51.2%, respectively. A comparison between lumped crop area statistics with areal sums calculated from the classified satellite data gave the highest correspondence where the SMAP algorithm was used, followed by the maximum likelihood and neural network algorithms. Based on our application, we can therefore confirm the value of a multisource optical/SAR approach for analyzing landcover and the improvements to classification achieved using the SMAP algorithm. (C)Elsevier Science Inc., 2000.

  • 1218.
    Berre, Loik
    SMHI, Research Department, Atmospheric remote sensing.
    Estimation of synoptic and mesoscale forecast error covariances in a limited-area model2000In: Monthly Weather Review, ISSN 0027-0644, E-ISSN 1520-0493, Vol. 128, no 3, p. 644-667Article in journal (Refereed)
    Abstract [en]

    Statistical and balance features of forecast errors are generally incorporated in the background constraint of variational data assimilation. Forecast error covariances are here estimated with a spectral approach and from a set of forecast differences; autocovariances are calculated with a nonseparable scheme, and multiple linear regressions are used in the formulation of cross covariances. Such an approach was first developed for global models; it is here adapted to ALADIN, a bi-Fourier high-resolution limited-area model, and extended to a multivariate study of humidity forecast errors. Results for autocovariances confirm the importance of nonseparability, in terms of both vertical variability of horizontal correlations and dependence of vertical correlations with horizontal scale; high-resolution spatial correlations are obtained, which should enable a high-resolution analysis. Moreover nonnegligible relationships are found between forecast errors of humidity and those of mass and wind fields.

  • 1219. Tuomenvirta, H
    et al.
    Alexandersson, Hans
    SMHI.
    Drebs, A
    Frich, P
    Nordli, P O
    Trends in Nordic and Arctic temperature extremes and ranges2000In: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 13, no 5, p. 977-990Article in journal (Refereed)
    Abstract [en]

    The national meteorological institutes in the Nordic countries have produced a comprehensive dataset of climatic extreme temperatures (monthly mean daily maximum and minimum, and monthly absolute highest and lowest temperatures) comprising stations from Fenno-Scandia, the Nordic Seas, and Greenland. Mean maximum and minimum temperatures show statistically significant negative trends in western coastal Greenland during the period 1950-95, while over the Nordic Seas and Fenno-Scandia the trends are generally positive. The diurnal temperature range (DTR) is decreasing significantly throughout the study area and is unrelated to regional temperature trends, which show both warming and cooling. The opposite temperature trends between western coastal Greenland and Fenno-Scandia since the 1950s are in accordance with a strengthening of the North Atlantic Oscillation (NAO). However, the simple NAO index fails to explain the decrease of DTR. In Fenno-Scandia, the reliable long-term mean maximum and minimum temperatures show cooling in winter and warming in spring and summer during the period 1910-95. Simultaneously, DTR has been decreasing in all seasons except winter. Most of the decrease has occurred since the 1940s. Atmospheric circulation indices defined by zonal and meridional sea level pressure differences, along with sea level pressure and cloud cover anomalies were used to build a multiple linear regression model for the Fenno-Scandian DTR. During the period 1910-95 the model explains from 53% (winter) to 80% (summer) of the variation in DTR and reproduces the statistically significant decreasing trend on annual level. Cloud cover is the dominant predictor, while circulation provides substantial improvement in explanation.

  • 1220. Kaurola, J
    et al.
    Taalas, P
    Koskela, T
    Borkowski, J
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Long-term variations of UV-B doses at three stations in northern Europe2000In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 105, no D16, p. 20813-20820Article in journal (Refereed)
    Abstract [en]

    Recent analysis of the total ozone observations indicate a negative trend of about 4%/decade in the Northern Hemisphere midlatitudes during the last two decades [WMO, 1999]. The effect of this decline on surface UV levels is of interest to a variety of applications. In this work the long-term variation of UV radiation at three stations located in northern Europe (Belsk, Norrkoping, and Jokioinen) has been studied using data from (1) ground-based observations, (2) surface UV doses determined using TOMS satellite measurements, and (3) reconstructed UV doses using observations of global radiation, total ozone, and radiative transfer modeling. For each station the estimates of daily UV doses from various sources have been intercompared, and a trend analysis has been performed to reveal long-term changes in the UV radiation. Data sets, which start in the late 1970s or early 1980s, show a general positive trend in annual doses of UV radiation. Some of these upward trends are statistically significant. For Belsk the increases are in the range of 5-15% per decade during spring and summer. The largest increases, about 20%/decade, has been observed in Norrkoping during spring. At Jokioinen there has been a slight upward trend in UV throughout the year. The analysis of reconstructed Belsk data from 1966 onward shows that the positive trend since late 1970s was preceeded by a negative trend. The reason for such changes is probably not only related to the changes in the total ozone but also to changes in aerosol content and cloudiness. The agreement of the UV series based on different data sources is good. This was studied using a subset of data in which it was required that data from all possible sources were available. The different trend estimates were in very close agreement with each other. However, there were often differences in absolute values, which is probably related to problems in calibration and limitations of the models.

  • 1221.
    Josefsson, Weine
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Landelius, Tomas
    SMHI, Research Department, Atmospheric remote sensing.
    Effect of clouds on UV irradiance: As estimated from cloud amount, cloud type, precipitation, global radiation and sunshine duration2000In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 105, no D4, p. 4927-4935Article in journal (Refereed)
    Abstract [en]

    Ten years of measurements of UV irradiance, monitored by the Robertson-Berger (RB) meter in Norrkoping, 58.58 degrees N, 16.15 degrees E, Sweden, have been combined with concurrent synoptic cloud observations, measurements of sunshine duration, and global radiation to establish the relative influence of clouds on UV irradiance. It is shown that the cloud effect for UV wavelengths is less than for the whole solar spectrum (global radiation). Relations retrieved for global radiation may be used by correcting for the differences. High-level clouds are more transparent than low- and medium-level clouds. As expected, it was found that precipitating clouds in general are more opaque than nonprecipitating clouds. If there is any solar elevation dependency in the effect of clouds, it is small. Using only total cloud amount as parameter to model, the cloud effect on UV irradiance will give a substantial uncertainty, which can be decreased considerably using cloud type and/or information on precipitation conditions. It has also been shown that sunshine duration can be used in a similar way as cloud covet.

  • 1222.
    Landelius, Tomas
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Methods for cosine correction of broadband UV data and their effect on the relation between UV irradiance and cloudiness2000In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 105, no D4, p. 4795-4802Article in journal (Refereed)
    Abstract [en]

    Irradiance measurements on a horizontal surface often deviate from theory where the irradiance is supposed to be proportional to the cosine of the angle of incidence. This discrepancy is known as the cosine error. In this paper, three different methods for cosine error correction are investigated. The simplest method is based on the assumption of an isotropic sky radiance distribution, regardless of sky conditions, and the irradiance is treated as a single component. In the second method the irradiance is divided into one direct solar and one diffuse sky component, where the latter is assumed to have an isotropic distribution. Finally, a third method also divides the irradiance into two components but under the assumption of an anisotropic sky radiance distribution. Irradiances under general sky conditions are found by interpolation between clear and overcast cases on the basis of sunshine duration or cloud cover. The three methods are applied to data from a Robertson-Berger sunburning meter located in Norrkoping, Sweden. Both methods, where the irradiance is divided into two components, produce acceptable and similar results, while the isotropic one-component method does not.

  • 1223.
    Lidén, Rikard
    SMHI, Research Department, Hydrology.
    A new approach for estimating suspended sediment yield1999In: Hydrology and Earth System Sciences, ISSN 1027-5606, E-ISSN 1607-7938, Vol. 3, no 2, p. 285-294Article in journal (Refereed)
    Abstract [en]

    A semi-distributed conceptual model, HBV-SED, for estimation of total suspended sediment concentration and yield at the outlet of a catchment was developed and tested through a case study. The base of the suspended sediment model is a dynamic hydrological model, which produces daily series of areal runoff and rainfall for each sub-basin as input to the sediment routine. A lumped measure of available sediment is accumulated continuously based on a linear relationship between log-transformed values of rainfall and erosion, while discharge of suspended sediment at the sub-basin outlet is dependent on runoff and amount of stored available sediment. Four model parameters are empirically determined through calibration against observed records of suspended sediment concentration. The model was applied to a 200 km(2) catchment with high altitude differences in the tropical parts of Bolivia, where recorded suspended sediment concentrations were available during a two-year period. 10,000 parameter sets were generated through a Monte Carlo procedure to evaluate the parameter sensitivity and interdependence. The predictability of the model was assessed through dividing the data record into a calibration and an independent period for which the model was validated and compared to the sediment rating curve technique. The results showed that the slope coefficients of the log-transformed model equations for accumulation and release were much stronger than the intercept coefficients. Despite an existing interdependence between the model parameters, the HBV-SED model gave clearly better results than the sediment rating curve technique for the validation period, indicating that the supply-based approach has a promising future as a tool for basic engineering applications.

  • 1224. Laznik, M
    et al.
    Stalnacke, P
    Grimvall, A
    Wittgren, Hans B.
    SMHI.
    Riverine input of nutrients to the Gulf of Riga - temporal and spatial variation1999In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 23, no 1-3, p. 11-25Article in journal (Refereed)
    Abstract [en]

    Riverine transport is the, most important pathway for input of nutrients to the Gulf of Riga. The present study focused on updating existing estimates of the riverine nutrient contributions and on improving the favailable information on temporal and spatial variation in such input. The results show that the gulf received an average of 113,300 tons of nitrogen, 2050 tons of phosphorus and 64,900 tons of dissolved silica (DSi) annually during the time period 1977-1995. There was large interannual variation in loads, e.g., a factor two difference was found between the two most extreme years (1984 and 1990); this was attributed mainly to natural variation in water discharge. The seasonal distribution of nutrient loads exhibited a distinct pattern for practically all studied constituents, especially nitrate. Loads were high during the spring-flow and relatively low during the low-flow summer period. Examination of the spatial variation of nutrient loads showed that the Daugava River alone accounted for approximately 60% of the total riverine load. The highest area-specific loads of nitrate and phosphate were observed in the agriculturally dominated Lielupe River, and the highest loads of organic-nitrogen (org-N) and total phophorus (tot-P) were found in the Parnu River. However, the values for all the studied rivers and constituents were rather low (phosphorus) or moderate (nitrogen and silica) compared to those reported for many other drainage areas of the Baltic Sea. This was true despite the inefficient sewage treatment and intensive agriculture in the studied basins in the 1970s and 1980s. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 1225.
    Marmefelt, Eleonor
    et al.
    SMHI, Professional Services.
    Arheimer, Berit
    SMHI, Research Department, Hydrology.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    An integrated biogeochemical model system for the Baltic Sea1999In: Hydrobiologia, ISSN 0018-8158, E-ISSN 1573-5117, Vol. 393, p. 45-56Article in journal (Refereed)
    Abstract [en]

    The Swedish Meteorological and Hydrological Institute (SMHI) is developing an integrated biogeochemical model system for the Baltic Sea. It consists of three coupled models; a marine biogeochemical-hydrodynamical model (SCOBI), a continuous riverine nitrogen transport model (HBV-N) and an atmospheric transport and chemical model (MATCH). It is supplied with a tool for presentation and analysis. The SCOBI model is a coupled one-dimensional model with high vertical resolution. Horizontal variations are taken into account by dividing the area into smaller boxes. The model includes primary phytoplankton production, nitrogen fixation and secondary zooplankton production. Nitrogen load from land is obtained through the HBV-N model, which simulates organic and inorganic nitrogen separately in catchments. The model is based on the hydrological model HBV, and the subbasin runoff is simulated on a daily basis. The HBV-N model is calibrated and validated against measured concentrations and water flow in rivers. The atmospheric input of oxidised and reduced nitrogen is taken from the annual assessments carried out with the MATCH-Sweden modelling system. MATCH-Sweden combines model calculations, using an atmospheric transport and chemical model, with observations of air- and precipitation chemistry data to give a detailed mapping of concentrations and deposition of nitrogen compounds over Sweden. Supplemented with monitoring data for the specific area of interest, the integrated biogeochemical model system makes a useful tool for environmental protection analyses; e.g. for interpretation of monitoring data as well as creating scenarios for studies of effects in changes of the nutrient loads.

  • 1226.
    Bergström, Sten
    et al.
    SMHI, Research Department, Hydrology.
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    Abstract to "On the scale problem in hydrological modelling" [Journal of Hydrology 211 (1998) 253-265]1999In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 217, no 3-4, p. 284-284Article in journal (Refereed)
  • 1227.
    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.

  • 1228.
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    Modeling runoff to the Baltic Sea1999In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 28, no 4, p. 328-334Article in journal (Refereed)
    Abstract [en]

    A large-scale hydrologic model of macroscale dimension for total daily runoff to the Baltic Sea has been developed using 25 subbasins ranging from 21000 to 144000 km(2). Daily synoptic input was calibrated against monthly recorded river flows. Reasonable model results for the water balance were obtained while keeping the level of detail to a minimum with a proven conceptual modeling approach. Important elements of the modeled water balance are presented for the five main Baltic Sea drainage basins. The model is used for cooperative research with both meteorological and oceanographic modeling within the Baltic Sea Experiment (BALTEX) and the Swedish Regional Climate Modelling Programme (SWECLIM). It provides off-line analysis for coupled model development and fills a needed role until truly coupled models become available. Furthermore, the model is suitable for operational applications and will be used to extend runoff records, fill in missing data, and perform quality checks on new observations.

  • 1229. Reichert, B K
    et al.
    Bengtsson, L
    Åkesson, Ove
    SMHI.
    A statistical modeling approach for the simulation of local paleoclimatic proxy records using general circulation model output1999In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 104, no D16, p. 19071-19083Article in journal (Refereed)
    Abstract [en]

    A statistical modeling approach is proposed for the simulation of local paleoclimatic proxy records using general circulation model (GCM) output, A method for model-consistent statistical downscaling to local weather conditions is developed which can be used as input for process-based proxy models in order to investigate to what extent climate variability obtained from proxy data can be represented by a GCM, and whether, for example, the response of glaciers to climatic change can be reproduced. Downscaling is based on a multiple linear forward regression model using daily sets of operational weather station data and large-scale predictors at various pressure levels obtained from reanalyses of the European Centre for Medium-Range Weather Forecasts, Composition and relative impact of predictors vary significantly for individual. stations within the area of investigation. Owing to a strong dependence on individual synoptic-scale patterns, daily data give the highest performance which can be further increased by developing seasonal-specific relationships. The model is applied to a long integration of a GCM coupled to a mixed layer ocean (ECHAM4/MLO) simulating present-day and preindustrial climate variability. Patterns of variability are realistically simulated compared to observed station data within an area of Norway for the period 1868-1993.

  • 1230.
    Bärring, Lars
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Jonsson, P
    Achberger, C
    Ekstrom, M
    Alexandersson, Hans
    SMHI.
    The Lund instrumental record of meteorological observations: Reconstruction of monthly sea-level pressure 1780-19971999In: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 19, no 13, p. 1427-1443Article in journal (Refereed)
    Abstract [en]

    The reconstructed surface air pressure series from Lund, southern Sweden, covers the period 1780-1997 and comprises mon than 234000 valid observations (three observations per day), i.e. > 98% of all possible observation occasions. For the Early Instrumental Period (EIP; 1780-1860) data were digitised from the original records. For most of the Modern Instrumental Period (MIP; 1861-) a series was compiled from various databases containing instrument corrected data. During EIP, the series of raw monthly means show several substantial inhomogeneities. With the aid of a detailed reconstruction of the station history, it was possible to remove almost all inhomogeneities during EIP by applying the correct instrument corrections (for barometer temperature, to standard gravity and to mean sea-level pressure) to the series of original observations. In particular, corrections for the temperature and altitude of the barometer eliminated several inhomogeneities. A prerequisite for applying these corrections is the availability of high-resolution data (actual raw observations or daily averages). Further homogenisation was attained by intercomparison of the monthly mean pressure with acknowledged homogeneous series (mainly the UKMO monthly grid, station records from Copenhagen and Edinburgh). Statistical tests of homogeneity showed that no substantial inhomogeneities remain in the final version. The modern part of the final monthly pressure series largely follows that of the southern Baltic Sea region. Furthermore, it shows relatively high pressure during spring (MAM) in the period 1780-1820, which was paralleled by severe wind erosion in southern Scandinavia during this time. Relatively high pressure throughout the year is also notable during a period of precipitation deficit in 1970s. Copyright (C) 1999 Royal Meteorological Society.

  • 1231. Persson, K
    et al.
    Omstedt, Gunnar
    SMHI, Research Department, Air quality.
    Lenner, M
    Sjodin, A
    Svanberg, P A
    Estimation of trends in urban traffic NOx emissions by an empirical model1999In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 235, no 1-3, p. 367-369Article in journal (Refereed)
    Abstract [en]

    A model has been developed to estimate trends in urban traffic NOx emissions by measured NO2 concentrations. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 1232. Halldin, S
    et al.
    Bergstrom, H
    Gustafsson, D
    Dahlgren, L
    SMHI.
    Hjelm, P
    Lundin, L C
    Mellander, P E
    Nord, T
    Jansson, P E
    Seibert, J
    Stahli, M
    Kishne, A S
    Smedman, A S
    Continuous long-term measurements of soil-plant-atmosphere variables at an agricultural site1999In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 98-9, p. 75-102Article in journal (Refereed)
    Abstract [en]

    It is a major challenge in modem science to decrease the uncertainty in predictions of global climate change. One of the largest uncertainties in present-day global climate models resides with the understanding of processes in the soil-vegetation-atmosphere-transfer (SVAT) system. Continuous, long-term data are needed to correctly quantify balances of water, energy and CO2 in this system and to correctly model them. It is the objective of this paper to demonstrate how a combined system of existing sensor, computer, and network technologies could be set up to provide continuous and reliable long-term SVAT-process data from an agricultural site under almost all weather conditions. A long-term climate-monitoring system within the framework of NOPEX was set up in 1993-1994 at the Marsta Meteorological Observatory (MMO). It is situated in a flat agricultural area where annual crops are cultivated on a heavy clay soil. It has successfully monitored relevant states and fluxes in the system, such as atmospheric fluxes of momentum, heat, water vapour and CO2, atmospheric profiles of wind speed, direction, and temperature, short- and long-wave radiation, soil temperature, soil-water contents, groundwater levels, and rainfall and snow depth. System uptime has been more than 90% for most of its components during the first 5 years of operation. Results from the first 5 years of operation has proven MMO to be an ideal site for intercomparison and intercalibration of radiometers and fast turbulence sensors, and for evaluation of other sensors, e.g., rain gauges. The long time series of radiation data have been valuable to establish numerical limits for a set of quality-control flags. MMO has served as a boundary-layer research station and results from NOPEX campaigns show how the dimensionless wind gradient depends not only on the traditional stability parameter z/L but also on the height of the convective boundary layer. Measurements at the observatory grounds and a neighbouring field show a considerable variability in surface properties, which must be accounted for when assessing budgets of heat and other scalars. Questions concerning long-term calibration plans, maintenance of sensors and data-collection system, and continuous development of the computer network to keep it up to date are, however, only partly of interest as a research project in itself. It is thus difficult to get it funded from usual research-funding agencies. The full value of data generated by the: MMO system can best be appreciated after a decade or more of continuous operation. Main uses of the data would be to evaluate how SVAT models handle the natural variability of climate conditions, quantification of water, carbon and energy budgets during various weather conditions, and development of new parameterisation schemes in global and regional climate models. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 1233.
    Bringfelt, Björn
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Heikinheimo, M
    Gustafsson, Nils
    SMHI, Research Department, Meteorology.
    Perov, Veniamin
    SMHI, Research Department, Meteorology.
    Lindroth, A
    A new land-surface treatment for HIRLAM - comparisons with NOPEX measurements1999In: Agricultural and Forest Meteorology, ISSN 0168-1923, E-ISSN 1873-2240, Vol. 98-9, p. 239-256Article in journal (Refereed)
    Abstract [en]

    In order to improve the accuracy of forecasting near-surface atmospheric variables over a heterogeneous landscape, a framework of subgrid surface types and the ISBA parameterisation scheme for land surfaces have been tested in the operational weather forecast model HIRLAM, using a 5.5 km grid resolution. Surface energy fluxes measured during a single summer day at six fixed sites in the NOPEX area, representing agricultural fields, boreal forests and lakes, were used for verification. Both, in-situ field measurements and the HIRLAM simulation indicated that the Bowen ratio over forests was about twice as large as that of adjacent agricultural fields. This difference could be explained by the more effective turbulent mixing and larger surface resistance associated with the forest, thus making the sensible heat flux relatively large there. The use of initial soil moisture from a routine hydrological model gave improved agreement with measured surface fluxes and radiosonde temperature and humidity profiles compared to initialising from routine HIRLAM surface data. The differences in heat fluxes between the various surface types were also demonstrated by airborne flux measurements flown along a track at a height of ca. 100 m above the terrain. Modelled heat fluxes along the flight track were considerably smoothed due to the grid resolution used, e.g. the effect of a lake in reducing grid-averaged sensible heat flux could only be weakly detected, because the lake surface represented only 10% of the grid area. When the proportion of a contrasting surface type (lake) was altered from 10 to 100%, the surface fluxes calculated for the lake surface were almost unchanged; the results of the comparison did not provide evidence that more complex aggregation schemes for heat fluxes than straightforward area-weighted averaging would be required. The hourly variation of the modelled and simulated heat fluxes during the day studied could not be directly compared, because the simulated cloudiness did not exactly match that observed at the field sites. When the simulated net radiation was replaced with direct measurements, the model-based estimates of sensible and latent heat fluxes were closer to the corresponding field measurements. The divergence of sensible heat flux with height, as inferred from the tower measurements made over the forest, were supported by the aircraft measurements and the HIRLAM simulations. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 1234.
    Rummukainen, Markku
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Isaksen, I S A
    Rognerud, B
    Stordal, F
    A global model tool for three-dimensional multiyear stratospheric chemistry simulations: Model description and first results1999In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 104, no D21, p. 26437-26456Article in journal (Refereed)
    Abstract [en]

    The paper presents a new global modeling tool, Stratospheric Chemical Transport Model 2. It has been developed for effective three-dimensional multiyear stratospheric chemistry studies, featuring an extensive chemistry scheme, heterogeneous processing on sulfate aerosols, and some polar stratospheric cloud processes. The transport algorithm maintains sub-grid-scale distributions and connects vertically the stratospheric layers, even in a coarse vertical grid. The model has been integrated for 49 months, recycling 1 year of precalculated transport from a middle atmosphere general circulation model. One year of daily National Centers for Environmental Prediction global analyses are used as temperatures. Diurnal cycles of photolysis rates are recalculated every 7 days to give interaction with ozone changes. The model is able to describe most of the geographical and seasonal ozone variability and the meridional distributions of ozone, reactive nitrogen, chlorine, and bromine. Stratospheric diurnal cycles for nitrogen, hydrogen, chlorine, and bromine species are captured in detail. The upper stratosphere ozone deficiency, typical to models, is large. Its sensitivity to different ways of tuning are explored. Midlatitude, rather than polar, wintertime processes have so far been the focus in this model tool. The present transport and grid resolution are not suited for realistic simulations at high latitudes. As there is only a limited inclusion of polar stratospheric cloud (PSC) microphysics, chemical processing in the cold polar lower stratosphere also cannot be well simulated. For example, the Antarctic ozone hole is not simulated, but the modeled chemistry should be suitable for warm Arctic winters when type II PSCs and particle sedimentation do not occur.

  • 1235.
    Vedin, Haldo
    et al.
    SMHI.
    Eklund, Anna
    SMHI, Core Services.
    Alexandersson, Hans
    SMHI.
    The rainstorm and flash flood at Mount Fulufjallet in August 1997: The meteorological and hydrological situation1999In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 81A, no 3, p. 361-368Article in journal (Refereed)
    Abstract [en]

    The flood at Mount Fulufjallet, 30-31 August 1997 was caused by the most furious rainstorm ever documented in Sweden. Private measurements on the mountain show nor less than 276 mm over 24 hours, and the distribution of severe damage suggests even higher amounts in other parts of the mountain. The precipitation was connected to a front attacking a high pressure that had been dominating the weather in Sweden for several weeks, but orographic lifting on the east-facing slopes of the mountain may partly have caused the extreme intensity. In River Fulan. one of the upper branches of River Dalalven, the discharge peaked at a diurnal mean value of 233 m(3)/s, the highest since measurements began in 1913. At the stream Tangan and the new common outlet of the streams Store and Lilla Goljan, both locations with a normal discharge of only around 1 m(3)/s, instantaneous values of approximately 300 m(3)/s have been estimated, corresponding to values close to the normal discharge at the mouth of River Dalalven on the coast of the Sea of Bothnia.

  • 1236.
    Robertson, Lennart
    et al.
    SMHI, Research Department, Air quality.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Engardt, Magnuz
    SMHI, Research Department, Air quality.
    An Eulerian limited-area atmospheric transport model1999In: Journal of applied meteorology (1988), ISSN 0894-8763, E-ISSN 1520-0450, Vol. 38, no 2, p. 190-210Article in journal (Refereed)
    Abstract [en]

    A limited-area, offline, Eulerian atmospheric transport model has been developed. The model is based on a terrain-following vertical coordinate and a mass-conserving, positive definite advection scheme with small phase and amplitude errors. The objective has been to develop a flexible, all purpose offline model. The model includes modules for emission input, vertical turbulent diffusion, and deposition processes. The model can handle an arbitrary number of chemical components and provides a framework for inclusion of modules describing physical and chemical transformation processes between different components. Idealized test cases, as well as simulations of the atmospheric distribution of Rn-222, demonstrate the ability of the model to meet the requirements of mass conservation and positiveness and to produce realistic simulations of a simple atmospheric tracer.

  • 1237.
    Lidén, Rikard
    et al.
    SMHI, Research Department, Hydrology.
    Vasilyev, A
    Stalnacke, P
    Loigu, E
    Wittgren, Hans Bertil
    SMHI, Research Department.
    Nitrogen source apportionment - a comparison between a dynamic and a statistical model1999In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 114, no 2-3, p. 235-250Article in journal (Refereed)
    Abstract [en]

    A dynamic model, HBV-N, and a statistical model, MESAW, for nitrogen source apportionment were compared regarding model performance, model uncertainty and user applicability. The HBV-N model simulates continuous series of nitrogen concentrations with meteorological data and sub-basin characteristics as input. Diffuse nitrogen emissions are defined as regional model parameters which are calibrated by comparison of observed and simulated nitrogen data. The MESAW model uses nitrogen loads for a fixed time interval at each monitoring site as response variable and sub-basin characteristics as explanatory variables to estimate diffuse nitrogen emissions through non-linear regression analysis. The two models were applied in the Matsalu Bay watershed (3640 km(2)) in Estonia and the same land use and point sources data were used as input. Both models gave similar levels of diffuse total nitrogen emissions and retention rates, which also fit well with previous estimates made in Estonia and Scandinavia. A sensitivity analysis of the model parameters also showed similar uncertainty levels, which indicated that the model uncertainty was more dependent on the availability of nitrogen data and land cover distribution than the choice of model. Furthermore, the sensitivity analysis showed a parameter interdependency in both models, which implied the risk of compensation between estimated diffuse emissions and retention. In conclusion, however, the study showed that both models were capable of estimating nitrogen leakage from the dominating land classes and giving reliable source apportionment from the available input data. The study indicated that the HBV-N model has its advantage in assessments where detailed outputs are needed and when run-off data are limited, while the statistical MESAW model has its advantage in extensive studies since it is easily applied to large watersheds that have dense monitoring networks. (C) 1999 Elsevier Science B.V. All rights reserved.

  • 1238.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    On the effects of horizontal diffusion, resolution and orography on precipitation forecasting in a limited area model1999In: Meteorological Applications, ISSN 1350-4827, E-ISSN 1469-8080, Vol. 6, no 1, p. 49-58Article in journal (Refereed)
    Abstract [en]

    Precipitation forecasting experiments have been carried out with HIRLAM, a numerical weather prediction model. The model has been run with three different horizontal gridlengths: 22, 11 and 5.5 Km. An attempt has been made to estimate the appropriate magnitude of the horizontal diffusion, which is used to control small-scale noise in the model, by looking at Kinetic energy spectra. It is shown that, for the higher resolutions, smoothing the orography gives smoother precipitation patterns. The small-scale precipitation resulting from runs with the original orography has negligible extra skill compared to the smoothed orography runs. The results show that the model is able to forecast good precipitation amounts, even with 22 Km gridlengths. No significant improvements occur when the higher horizontal resolutions are used. Experiments have been performed using the tendencies of the physical parameterisations computed on a coarser grid than that of the dynamics. The resulting precipitation patterns are very similar and this indicates a more economical way of integrating the model.

  • 1239.
    Räisänen, Jouni
    SMHI, Research Department, Climate research - Rossby Centre.
    Internal variability as a cause of qualitative intermodel disagreement on anthropogenic climate changes1999In: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 64, no 1-2, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The qualitative agreement of two climate models, HADCM2 and ECHAM3, on the response of surface climate to anthropogenic climate forcing in the period 2020-2049 is studied. Special attention is paid to the role of internal climate variability as a source of intermodel disagreement. After illustrating the methods in an intermodel comparison of simulated changes in June-August mean precipitation, some global statistics are presented. Excluding surface air temperature, the four-season mean proportion of areas in which the two models agree on the sign of the climatic response is only 53-60% both for increases in CO2 alone and for increases in CO2 together with direct radiative forcing by sulphate aerosols, but somewhat larger, 59-70% for the separate aerosol effect. In areas where the response is strong (at least twice the standard error associated with internal variability) in both models, the agreement is better and the contrast between the different forcings becomes more marked. The proportion of agreement in such areas is 57-75% for the response to increases in CO2 alone, 64-84% for the response to combined CO2 and aerosol forcing, and as high as 88-94% for the separate aerosol effect. The relatively good intermodel agreement for aerosol-induced climate changes is suggested to be associated with the uneven horizontal distribution of aerosol forcing.

  • 1240.
    Engardt, Magnuz
    et al.
    SMHI, Research Department, Air quality.
    Holmen, K
    Model simulations of anthropogenic-CO2 transport to an Arctic monitoring station during winter1999In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 51, no 2, p. 194-209Article in journal (Refereed)
    Abstract [en]

    We describe, and use, a limited area, 3-dimensional transport model. The model domain is located over the Arctic, but includes the majority of the anthropogenic CO2 emissions in western and eastern Europe, which together make up about 1/3 of the global CO2 emissions. The model is run for several winter periods, using anthropogenic CO2 emissions only, and the results are compared with independent CO2 measurements taken at a monitoring station on Spitsbergen in the high Arctic. We show that the initial concentrations and boundary values of the domain are not crucial for the results, and conclude that most of the measured variability above the winter baseline in CO2 at the Arctic monitoring station emanates from recent CO2 sources within the model domain. From the observed small spatial variability in the monthly mean atmospheric CO2 mixing ratio in the north Atlantic region, we assume that there is only little net exchange between the atmosphere and ocean during the studied periods. Based on the co-variation between CO2 and particulate mass,we hypothesise that most of the measured CO2 variability is due to anthropogenic fossil fuel emissions, although we can not rule out a biogenic CO2 component. Using the transport model, we compare different estimates of fossil-fuel consumption in the mid-latitudes. We find that the industrial centres and the surrounding gas-fields in the lower-Ob region (60 degrees-72 degrees N, 65 degrees-80 degrees E) occasionally have a much larger impact on the CO2 measurements at Spitsbergen than follows from a recent CO2 emission inventory. This implies that there may be an overlooked CO2 source in this region, possibly flaring of gas.

  • 1241. Heino, R
    et al.
    Brazdil, R
    Forland, E
    Tuomenvirta, H
    Alexandersson, Hans
    SMHI.
    Beniston, M
    Pfister, C
    Rebetez, M
    Rosenhagen, G
    Rosner, S
    Wibig, J
    Progress in the study of climatic extremes in northern and central Europe1999In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 42, no 1, p. 151-181Article in journal (Refereed)
    Abstract [en]

    A study of the long-term changes of various climatic extremes was made jointly by a number of European countries. It was found that the changes in maximum and minimum temperatures follow, in broad terms, the corresponding well-documented mean temperature changes. Minimum temperatures, however, have increased slightly more than maximum temperatures, although both have increased. As a result, the study confirms that the diurnal temperature range has mostly decreased during the present century in Northern and Central Europe. Frost has become less frequent. Two extreme-related precipitation characteristics, the annual maximum daily precipitation and the number of days with precipitation greater than or equal to 10 mm, show no major trends or changes in their interannual variability. An analysis of return periods indicated that in the Nordic countries there were high frequencies of 'extraordinary' 1-day rainfalls both in the 1930s and since the 1980s. There have been no long-term changes in the number of high wind speeds in the German Eight. Occurrences of thunderstorms and hails show a decreasing tendency in the Czech Republic during the last 50 years. Finally, using proxy data sources, a 500-year temperature and precipitation event graph for the Swiss Mittelland is presented. It shows large interdecadal variations as well as the exceptionality of the latest decade 1986-1995.

  • 1242.
    Omstedt, Anders
    et al.
    SMHI, Research Department, Oceanography.
    Axell, Lars
    SMHI, Research Department, Oceanography.
    Modeling the seasonal, interannual, and long-term variations of salinity and temperature in the Baltic proper1998In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 50, no 5, p. 637-652Article in journal (Refereed)
    Abstract [en]

    Salinity and temperature variations in the Baltic proper and the Kattegat have been analyzed with a numerical ocean model and a large amount of observational data. In the model, the Baltic Sea is divided into 13 sub-basins with high vertical resolution, horizontally coupled by barotropic and baroclinic flows and vertically coupled to a sea-ice model which includes dynamics as well as thermodynamics. The model was integrated for a 15-year period (1980-1995) by using observed meteorological forcing data, river-runoff data and sea-level data from the Kattegat. The calculated 15-year median profiles of salinity and temperature in the different sub-basins are in good agreement with observations. However, the calculated mid-depth salinities in the Arkona Basin and Bornholm Basin were somewhat overestimated, and the calculated deep-water temperatures in the Arkona Basin and the Bornholm Basin are somewhat lower than the observed values. Frontal mixing and movements in the Kattegat and the entrance area of the Arkona Basin were important to consider in the model. Water masses were simulated well, and prescribing constant deep-water properties in the Kattegat proved to be a reasonable lateral boundary condition. Further, comparisons were made between observed and calculated seasonal and interannual variations of the hydrographic properties in the Eastern Gotland Basin, as well as the interannual variations of the annual maximum ice extent. We conclude that the model can simulate these variations realistically. The major Baltic inflow of 1993 was also simulated by the model, but the inflowing water was 1-2 degrees degrees too cold. Finally, the response times to changes in forcing of the Baltic proper and the Kattegat were investigated by performing the so-called lock-exchange experiment. Typical stratification spin-up times were of the order of 10 years for the Kattegat, and 100 years for the Baltic proper.

  • 1243.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Nyberg, Leif
    SMHI.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Coupling of a high-resolution atmospheric model and an ocean model for the Baltic Sea1998In: Monthly Weather Review, ISSN 0027-0644, E-ISSN 1520-0493, Vol. 126, no 11, p. 2822-2846Article in journal (Refereed)
    Abstract [en]

    The coupling between a high-resolution weather forecasting model and an ocean model is investigated. It is demonstrated by several case studies that improvements of short-range weather forecasting in the area of the Baltic Sea require an accurate description of the lower boundary condition over sea. The examples are taken from summer situations without sea ice as well as from winter situations with extreme sea ice conditions. It is shown that the sea state variables used in the model influence the weather forecast both directly on the local scale due to the local impact of surface fluxes of latent and sensible heat and on regional and larger scales. The convective snowbands during winters with cold airmass outbreaks over the open water surfaces of the Baltic Sea are extreme examples of the influence of sea state variables on a regional scale, It is furthermore demonstrated that the sea state conditions may change considerably within forecasting periods up to 48 h. This implies the necessary application of ocean models, two-way interactively coupled to the weather forecasting model. The coupling of an advanced 2.5-dimensional ice-ocean model to the operational Swedish Meteorological and Hydrological Institute (SMHI) weather forecasting model HIRLAM is described. The ice-ocean model includes two-dimensional, horizontally resolved ice and storm surge models and a one-dimensional, vertically resolved ocean model applied to 31 Baltic Sea regions. The coupled model system is applied operationally in a data assimilation system at the SMHI. No data assimilation is applied in the operational ocean component: manual modifications to the sea state variables are introduced a few times every winter season. The application of this operational coupled model data assimilation system to the mesoscale reanalysis for the Baltic Sea Experiment (BALTEX) shows that it is necessary to apply data assimilation fur the sea state variables in order to avoid drift of the coupled model system toward less realistic model states. A successful application of a simple assimilation of SST observations is presented. The observed SSTs are first subject to a horizontal filter in order to minimize the effects of observational errors and to restrict the influence to a larger horizontal scale. Then the differences between these filtered temperature observations and the model SSTs are used to construct a modified sensible heat Aux that is applied as a form of a "nudging" term to the ocean model. It turns out that this "nudging" is successful in avoiding the drift away from realistic sea state conditions. The described atmosphere and ocean data assimilation scheme has been applied in a rerun of the BALTEX mesoscale reanalysis for the cold winter 1986/87. The quality of this reanalysis was assessed through the successful simulation of the convective snowbands in January 1987.

  • 1244.
    Svensson, Urban
    et al.
    SMHI, Research Department, Oceanography.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Numerical simulations of frazil ice dynamics in the upper layers of the ocean1998In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 28, no 1, p. 29-44Article in journal (Refereed)
    Abstract [en]

    The frazil ice dynamics in a turbulent Ekman layer have been investigated using a mathematical model. The model is based on the conservation equations for mean momentum, energy and salinity, and employs a two-equation turbulence model for the determination of turbulent diffusion coefficients. A crystal number continuity equation is used for the prediction of the frazil ice dynamics. This equation considers several processes of importance, as for example turbulent diffusion, gravitational up-drift, flocculation/break-up and growth. The results focus on the frazil ice characteristics in the upper layers of the ocean, like suspended ice volume, ice crystals per m(3), vertical distributions, etc. From the idealized calculations, it is indicated that a large number of ice crystals can be mixed into the ocean during freezing. However, the amount of ice in suspension, measured as vertically integrated ice thickness, adds only a minor part to the total surface ice budget. Small crystals are mixed deep in the ocean while the large ones are found only in the top of the mixed layer. Knowledge about the vertical distribution of ice crystals of different sizes, which is calculated from the model, should be of importance when analysing processes as formation of ice covers in the ocean and ice-sediment or ice-algae interaction. (C) 1998 Elsevier Science B.V. All rights reserved.

  • 1245.
    Bergström, Sten
    et al.
    SMHI, Research Department, Hydrology.
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    On the scale problem in hydrological modelling1998In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 211, no 1-4, p. 253-265Article in journal (Refereed)
    Abstract [en]

    The problem of scales and particularly the modelling of macro or continental scale catchments in hydrology is addressed. It is concluded that the magnitude of the scale problem is related to the specific hydrologic problem to be solved and to the scientific approach and perspective of the modeller. A distributed modelling approach, based on variability parameters, is suggested for modelling of soil moisture dynamics and runoff generation. It is shown that the parameters of such an approach are relatively stable over a wide range of scales. An example of the application of a standard Version of the Swedish HBV hydrological model to the continental scale catchment of the Baltic Sea is shown and its usefulness is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.

  • 1246.
    Arheimer, Berit
    et al.
    SMHI, Research Department, Hydrology.
    Brandt, Maja
    SMHI, Research Department, Hydrology.
    Modelling nitrogen transport and retention in the catchments of southern Sweden1998In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 27, no 6, p. 471-480Article in journal (Refereed)
    Abstract [en]

    The Baltic Sea is suffering from eutrophication and attempts are being made to reduce nutrient loads. This article focuses on nitrogen transport from southern Sweden (145 000 km(2)), and presents a model approach (HBV-N) that has been used in the national decision-making process for best management practices. Calculations of nitrogen leaching, retention in the freshwater system, net transport to the sea, and source apportionment are presented for the period 1985-1994. Input data were handled in GIS, including results from SOIL-N and MATCH. Daily simulations were made in 3725 subbasins with calibration against measured time series at 722 sites. Diffuse source pollution was normally retained by 10-25% before entering the river network. Lakes normally reduced nitrogen transport by 30-40 kg ha(-1) yr(-1) of lake area. On average, 45% of the annual gross load was reduced during transport, but temporal and spatial variations were great. 75 000 tonnes N yr(-1) reached the sea.

  • 1247.
    Axell, Lars
    SMHI, Research Department, Oceanography.
    On the variability of Baltic Sea deepwater mixing1998In: JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, Vol. 103, no C10, p. 21667-21682Article in journal (Refereed)
    Abstract [en]

    Historical oceanographic data from the period 1964-1997 from two deep subbasins (the Gotland Deep and the Landsort Deep) in the Baltic Sea have been analyzed, by using a budget method on stagnant periods, with respect to vertical diffusion and vertical energy flux density in the deep water. It was found that the rate of deepwater mixing varied with the seasons, with higher rates in fall and winter compared to spring and summer. Further, according to the analyzed data, the downward flux density of energy available for vertical diffusion decreased with increasing depth in the Gotland Deep. In the Landsort Deep, however, the flux density increased somewhat, probably because of topographic concentration of the energy, before decreasing toward the bottom. Moreover, the vertical energy flux densities were compared with the expected flux density from the local wind. It is proposed that in the Gotland Deep, which is outside the coastal boundary layer, the observed deepwater mixing is dominated by the energy input from the wind via inertial currents and internal waves. In the Landsort Deep, however, which is within the coastal boundary layer, the expected flux density of energy from the local wind cannot explain the observed rate of work against the buoyancy forces. It is proposed that the active coastal boundary layer plays a central role in the transfer of energy to mixing processes in the deep water.

  • 1248.
    Robertson, Lennart
    et al.
    SMHI, Research Department, Air quality.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Source function estimate by means of variational data assimilation applied to the ETEX-I tracer experiment1998In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 32, no 24, p. 4219-4225Article in journal (Refereed)
    Abstract [en]

    The ETEX data set opens new possibilities to develop data assimilation procedures in the area of long-range transport. This paper illustrates the possibilities using a variational approach, where the source term for ETEX-I was reconstructed. The MATCH model (Robertson et at., 1996) has been the basis for this attempt. The timing of the derived emission rates are in accordance with the time period for the ETEX-I release, and a cross validation, with observations beyond the selected assimilation period, shows that the source term gained holds for the entire ETEX-I experiment. A poor-man variational approach was shown to perform nearly as good as a fully variational data assimilation. The issue of quality control has not been considered in this attempt but will be an important part that has to be addressed in future work. (C) 1998 Elsevier Science Ltd. All rights reserved.

  • 1249. Peterson, T C
    et al.
    Easterling, D R
    Karl, T R
    Groisman, P
    Nicholls, N
    Plummer, N
    Torok, S
    Auer, I
    Boehm, R
    Gullett, D
    Vincent, L
    Heino, R
    Tuomenvirta, H
    Mestre, O
    Szentimrey, T
    Salinger, J
    Forland, E J
    Hanssen-Bauer, I
    Alexandersson, Hans
    SMHI.
    Jones, P
    Parker, D
    Homogeneity adjustments of in situ atmospheric climate data: A review1998In: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 18, no 13, p. 1493-1517Article in journal (Refereed)
    Abstract [en]

    Long-term in situ observations are widely used in a variety of climate analyses. Unfortunately, most decade- to century-scale time series of atmospheric data have been adversely impacted by inhomogeneities caused by, for example, changes in instrumentation, station moves, changes in the local environment such as urbanization, or the introduction of different observing practices like a new formula for calculating mean daily temperature or different observation times. If these inhomogeneities are not accounted for properly, the results of climate analyses using these data on be erroneous. Over the last decade, many climatologists have put a great deal of effort into developing techniques to identify inhomogeneities and adjust climatic time series to compensate for the biases produced by the inhomogeneities. It is important for users of homogeneity-adjusted data to understand how the data were adjusted and what impacts these adjustments are likely to make on their analyses. And it is important for developers of homogeneity-adjusted data sets to compare readily the different techniques most commonly used today. Therefore, this paper reviews the methods and techniques developed for homogeneity adjustments and describes many different approaches and philosophies involved in adjusting in situ climate data. (C) 1998 Royal Meteorological Society.

  • 1250.
    Langner, Joakim
    et al.
    SMHI, Research Department, Air quality.
    Robertson, Lennart
    SMHI, Research Department, Air quality.
    Persson, Christer
    SMHI, Research Department, Air quality.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Validation of the operational emergency response model at the Swedish Meteorological and Hydrological Institute using data from ETEX and the Chernobyl accident1998In: Atmospheric Environment, ISSN 1352-2310, E-ISSN 1873-2844, Vol. 32, no 24, p. 4325-4333Article in journal (Refereed)
    Abstract [en]

    The Eulerian atmospheric tracer transport model MATCH (Multiscale Atmospheric Transport and Chemistry model) has been extended with a Lagrangian particle model treating the initial dispersion of pollutants from point sources. The model has been implemented at the Swedish Meteorological and Hydrological Institute in an emergency response system for nuclear accidents and can be activated on short notice to provide forecast concentration and deposition fields. The model has been used to simulate the transport of the inert tracer released during the ETEX experiment and the transport and deposition of Cs-137 from the Chernobyl accident. Visual inspection of the results as well as statistical analysis shows that the extent, time of arrival and duration of the tracer cloud, is in good agreement with the observations for both cases, with a tendency towards over-prediction for the first ETEX release. For the Chernobyl case the simulated deposition pattern over Scandinavia and over Europe as a whole agrees with observations when observed precipitation is used in the simulation. When model calculated precipitation is used, the quality of the simulation is reduced significantly and the model fails to predict major features of the observed deposition held. (C) 1998 Elsevier Science Ltd. All rights reserved.

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