An operational Baltic Sea circulation model : Part 1. Barotropic version

A vertically integrated barotropic model for the Baltic Sea is described both in dynamic and numerical 1terms. The model has been ron operationally since March 1993 on a 5 x 5 km grid and is forced by interpolated 10 m winds and surface pressure from the 50 x 50 km HIRLAM atmospheric mode!. The water volume is not conserved but depends on inflow from rivers and in- or outflow through the Belt Sea and the Öresund

Numerisk beräkning av vågor i kraftverksdammar

Kraftiga vågrörelser uppstår i kraftverksmagasin,  när avtappningen hastigt stryps. Detta kan vara fallet vid störningar i kraftverksdriften eller eldistributionsnätet.Om vattennivån i magasinet ligger nära dämningsgränsen, kan vågorna orsaka störningar i ytregleringsautomatiken och katastrofskyddet, samtidigt som dämningsgränsen kan överskridas. Liknande problem kan uppstå i korttidsreglerade magasin.Amplituder på upp till o.60 m har registrerats just vid utloppet (Stugun), medan längre uppströms endast registreras vågor med en amplitud mindre än 0.15 m. Initialt bildas vågor av flera frekvenser, och de högfrekventa och med högst  amplitud dämpas mycket kraftigt och försvinner efter 100 - 200 m. Vattenståndshöjningen, som orsakas av det plötsliga stoppet, är emellertid synlig i hela magasinet som en solitär våg med en amplitud av upp till 0.20 m. Dessutom uppstår egensvängningar i delbassänger nära utloppet med en amlitud på 0.05 - 0.15 m, vilket kan vara nog för att i vissa fall överskrida dämningsgränsen.Avsikten med den här redovisade studien är att utröna huruvida uppmätta vågor går att reproducera i en numerisk modell, och vidare om modellen kan tillämpas på godtyckligt magasin för studier av effekten av dessa vågor

En hydrodynamisk modell för spridnings- och cirkulationsberäkningar i Östersjön : Slutrapport

En modell för beräkning av föroreningars spridning i Östersjön har utvecklats vid SMHI Modellen behandlar spridning såväl horisontellt som vertikal och kan användas för spridningsstudier i en tidsskala från timmar till år. Biokemiska förlopp kan utan svårighet inkluderas 1 modellen. Modellen är ett lämpligt redskap för studier av pågående utsläpp, katastrofutsläpp och i samband med industrilokalisering. Kustområden med återkommande uppvällning kan identifieras med hjälp av modellen. Cirkulationsmodellen ger ett värdefullt bidrag till den allmänna kunskapen om Östersjöns dynamik

The dynamics of lake Vättern, preliminary results

Continuous current and temperature data were taken from one station in Lake Vättern during the 1977 surnrner. Further temperature data were collected from two stations by continuous recordings at eleven depths during a fortnight period. A three-dimensional hydrodynamic model has been applied to the lake. Observations of current and temperature show a good agreement with corresponding model results. Wave like motions have been studied through a method of rotary spectral analysis. It is suggested tha tobserved waves can be related to different modes of Poincaré waves. Motions with a period of several days were observed and have been interpreted in terms of internal Kelvin-waves. There also is evidence of motions with a frequency lower than the inertial value pointing towards nonlinear interactions between inertial motions and lower frequency currents.Föroreningssituationen i Vättern har sedan början på 60-talet mer i detalj kunnat föijas genom mätningar av biologiska och kemiska parametrar. Främst är det Vätterns växande betydelse som vattentäkt som föranlett en kontinuerlig provtagning. Även förändringar i fisket har aktualiserat en fortlöpande kontroll av föroreningssituationen. I en vattenvårdsplan (Kommitten för Vätterns vattenvård,1970) beskrivs utförda mätningar såväl före 1962 som under den mer intensiva perioden 1962-67.I vattenvårdsplanen påpekas också behovet av en noggrann kartläggning av strömningsförhållandena i sjön. Därigenom skulle möjligheterna ökas att bestämma spridningen och utspädningen av avloppsvatten från industrier. Samtidigt skulle detta underlätta en övergripande och långsiktig planering av Vätterns utnyttjande som vattenresurs. De enstaka mätningar av skiktningsförhållanden och strömhastigheter som tidigare utförts har indikerat komplicerade strömningsmönster. I denna rappor tredovisas kontinuerliga mätningar av ström och temperatur, vilka också jämförs med genererade strömmar och skiktningsförhållanden från en hydrodynamisk modell

An introduction to HIROMB, an operational baroclinic model for the Baltic Sea

A3-dimensional baroclinic model of the North Sea and the Baltic Sea, designed for a daily operational use is described in detail. The model is based on a similar model running in operational mode at the German Federal Maritime and Hydrographic Agency (BSH) in Hamburg, Germany. The operational forecasts started in 1995 with a daily 24-hour forecast and was later extended to 48 hours. The model is mainly forced by SMHI's operational atmospheric model (HIRLAM), but also by river runoff from an operational hydrological model and wave radition stress from a wind wave model. The present version of the model is set up on a nested grid where a 12 nautical mile (nm) grid covers the whole area while Skagerrak, Kattegat, the Belt Sea and the Baltic Sea are covered with a 1 nm grid. A parallelized version of the model has been developed and runs on a distributed memory parallel computer

A model for pollution studies in the Baltic Sea

A combination of a circulation anda diffusion model has been developed to be used for dispersion studies in the Baltic Sea. As the time scale of interest is from months up to several years a straightforward way to model the dispersion would require the circulation model to be run for a very long time, which would be impractible. Instead atypical meteorological year has been constructed for which the circulation model has been run. The circulation model is three-dimensional, uses six layers in the vertical and hasa horizontal resolution of 10 kilometres. The diffusion model is of Monte Carlo type in all three dimensions. So far only passive pollutants have been treated but the model will be extended to include biochemical interaction and sedimentation processes. Results of applications to three outlets are shown

Validation of HIROMB during 1995-96

IROMB (High Resolution Operational Model of the Baltic Sea) is the result of a combined effort between BSH (Bundesamt för Seeschiffahrt und Hydrographie) and SMHI (Swedish Meteorological and Hydrological Institute). In its present form, the model is a modified version of the BSH operational model (Kleine, 1994) with identical boundaries to the North Atlantic. The cooperation started in summer 1994 when the model was set up at SMHI. The first operational runs started in the sumrner 1995 and since then the model has been running daily except fora limited number of periods when there were no meteorological input from the HIRLAM (atmospheric) model available because of computer problems. During the first months, some occasions with stability problems occurred, leading toa restart from the climatological fields. This report presents results from a continous verification exercise, where model results are compared to observations of water level, surface temperature, currents, ice thickness and salinity and temperature profiles. The times series data are taken from the period September-November 1996 while the ice thickness data are from November and December 1996 and the sea surface temperature data are taken from August, November and December 1996. For a detailed description of the model, the reader is referred to a forthcoming report by Funkquist and Kleine

Validation of HIROMB during 1995-96

IROMB (High Resolution Operational Model of the Baltic Sea) is the result of a combined effort between BSH (Bundesamt för Seeschiffahrt und Hydrographie) and SMHI (Swedish Meteorological and Hydrological Institute). In its present form, the model is a modified version of the BSH operational model (Kleine, 1994) with identical boundaries to the North Atlantic. The cooperation started in summer 1994 when the model was set up at SMHI. The first operational runs started in the sumrner 1995 and since then the model has been running daily except fora limited number of periods when there were no meteorological input from the HIRLAM (atmospheric) model available because of computer problems. During the first months, some occasions with stability problems occurred, leading toa restart from the climatological fields. This report presents results from a continous verification exercise, where model results are compared to observations of water level, surface temperature, currents, ice thickness and salinity and temperature profiles. The times series data are taken from the period September-November 1996 while the ice thickness data are from November and December 1996 and the sea surface temperature data are taken from August, November and December 1996. For a detailed description of the model, the reader is referred to a forthcoming report by Funkquist and Kleine

Calculations of horizontal exchange coefficients using Eulerian time series current meter data from the Baltic Sea

A method is described which relates observed eularian current fluctuations to horizontal exchange coefficients. The method is applied to current meter time series from the southern and the central parts of the Baltic Proper and from the Bothnian Sea. Energy spectras suggest that current fluctuations with a time scale shorter than 24 hours can be considered as turbulence in large scale circulation models and parameterized by an exchange coefficient. The horizontal exchange is found to be horizontally uniform. The calculated exchange coefficients have a vertical variation ranging from 10-50 m s in the surface layer to 1-3 m s below 70 metres . Inertial or near-inertial oscillations are the most important physical processes that produce horizontal exchange

Tillämpning av en numerisk modell på Vänern

Current, temperature and water-level measurements in Lake Vänern from two epdisodes in 1971, representing a stratified resp anunstratified situation, have been used for the verification of an multilayer hydrodynamic model. Concentrating on wind-driven lake circulation it is shown that, aside from the currents along the western shore of the eastern basin, the correspondence between model results and observations is satisfactory. The computed currents could therefore be used for studies on the transport and dilution of wasterwater in the lake. It is also concluded that neither avariation of model parameters nor an increased vertical or horizontal resolution will make the model reproduce the strong and mainly south-going current along the western shore of the eastern half of the lake.Verifiering av en flerlagers hydrodynamisk modell tillämpad på Vänern har utförts med hjälp av ström-, temperatur- och vattenståndsvärden från två perioder 1971 (representerande skiktade resp oskiktade förhållanden). De beräknade strömmarna visas stämma väl överens med observerade data och bör därför kunna utgöra ett bra underlag vid studier av transportvägar och utspädningsgrad för olika typer av utsläpp. De relativt starka strömmarna i västra delen av Värmlandssjön har inte kunnat beskrivas i modellen trots försök med flera kombinationer av modellens parametervärden och ökad horisontell och vertikal upplösning