Papers by Øyvind Byrkjedal
Sjøisen i Arktis er en viktig komponent i klimasystemet, og spiller en stor rolle ved å vekselvir... more Sjøisen i Arktis er en viktig komponent i klimasystemet, og spiller en stor rolle ved å vekselvirke med atmosfaerens sirkulasjon gjennom endringer i overflate albedo og energiutveksling. For å studere responsen på atmosfaeren fra endrede sjøis og SST i Labradorhavet er en global atmosfaeremodell (ARPEGE/IFS) stilt opp. Et kontrolleksperiment er kjørt med klimatologisk isdekke og SST i Labradorhavet. To perturberte kjøringer, LABMAX og LABMIN, er kjørt med henholdsvis større isdekke/lavere SST og redusert isdekke/høyere SST i Labradorhavet. Ved hjelp av analyseverktøyet TRACK er det funnet en tydelig sørlig forflytning av stormbanene over nord Atlanteren ved å øke isdekket over det klimatologiske. En reduksjon i isdekke over det klimatologiske har kun gitt små endringer på stormbanene. En negativ feedbackmekanisme hvor isdekket i Labradorhavet inngår er foreslått. Økning av isdekket over det klimatologiske gir en sørlig forflytning av stormbanene og reduksjon i NAO-indeksen. Dette gir igjen endringer i atmosfaerens midlere sirkulasjon som gir reduksjon i isdannelsen i Labradorhavet.
Development of operational forecasting for icing and wind power at cold climate sites
Based on icing measurements from 12 meteorological stations in Sweden a methodology for calculati... more Based on icing measurements from 12 meteorological stations in Sweden a methodology for calculating icing from meso scale model data has been developed over the past 5 years. Operational data from seven wind farms in cold climate regions in Sweden (total of 272 MW and 111 individual turbines) have in addition been utilized to develop a state-of-the-art model for estimating production losses due to icing (IceLoss). Operational forecasting of energy production, icing and production losses due to icing has been carried out for the four wind farms which all experiences losses due to icing. The forecast simulations are run 4 times daily, each with a lead time of 48 hours. It is shown that the method is able to realistically describe the periods when ice is influencing the energy production for the wind farms. 63-82% of the time periods when icing is influencing the energy production are captured by the forecasts. Essential to forecast icing events is the ability to forecast the events at...
Simulating wind farms in the Weather Research and Forecast model, resolution sensitivities
Simulating wind farms in the Weather Research and Forecast model, resolution sensitivities.
Two different offshore wind atlases based on the meso-scale model WRF are presented and discussed... more Two different offshore wind atlases based on the meso-scale model WRF are presented and discussed in this paper. The Work is part of the EU-funded project NORSEWIND (Northern Seas Wind Index Database). Validations show that annual average wind speeds and windroses at hub-height (100m) are well represented by the model, while the model accuracy is poorer for vertical wind profile, wind shear parameters and static stability. Abstract
Journal of Physics: Conference Series
Ocean Dynamics
Accurate predictions of surface ocean waves in coastal areas are important for a number of marine... more Accurate predictions of surface ocean waves in coastal areas are important for a number of marine activities. In complex coastlines with islands and fjords, the quality of wind forcing significantly affects the results. We investigate the role of wind forcing on wave conditions in a fjord system partly exposed to open sea. For this reason, we implemented the wave model SWAN at the west coast of Norway using four different wind forcing. Wind and wave estimates were compared with observations from five measurement sites. The best results in terms of significant wave height are found at the sites exposed to offshore conditions using a wind input that is biased slightly high compared with the buoy observations. Positively biased wind input, on the other hand, leads to significant overestimation of significant wave height in more sheltered locations. The model also shows a poorer performance for mean wave period in these locations. Statistical results are supported by two case studies wh...
Ice detection on wind turbines using the observed power curve
Wind Energy, 2015
ABSTRACT
Inter--comparison of icing production loss models
Developing a method for predicting power loss due to icing is of great concern for developers loo... more Developing a method for predicting power loss due to icing is of great concern for developers looking to build wind farms in cold climate locations. As part of the Ice Wind project four different ice production loss models have been developed at DTU, Kjeller Vindteknikk, VTT, and WeatherTech Scandinavia. We have compared these models at 15 wind parks spread across Canada and Sweden for the winter of 2011-2012. The models were first fit using the winter of 2010-2011 for these same wind parks. To isolate the performance of the ice model and production loss model, all tests used the same meteorological model results provided by Vestas. The four methods are described briefly below. * The DTU approach involves using the iceBlade icing model to predict ice mass on the blade of the turbine from the meteorological results, and then uses a statistical model to estimate the production loss based on iceBlade and meteorological model inputs. * Kjeller uses the Makkonen icing model to estimate i...
The meso-scale model WRF has been set up with three nests with respectively 18km, 6km and 2 km ho... more The meso-scale model WRF has been set up with three nests with respectively 18km, 6km and 2 km horizontal resolution. The model has been run for 4 years and hourly data were stored. Simultaneous measurements were available from the Fino 1 platform, and a first comparison of the data has been carried out. Monthly and annual average wind speeds from the model compares very well with the observations. Also the four year Weibull distribution and wind rose from the model correspond well with the observed values. Based on the comparison it is concluded that the model is a reliable tool for characterising the average wind conditions, at least in this part of the North Sea. However, for the temporal variations of vertical stability and wind shear larger deviations between the model and the measurements are encountered, and before the model data are applied to for example wake modelling a more detailed study of the statistical properties of the model data are recommended. Comparison of the a...
Climate Dynamics, 2008
The current state-of-the-art general circulation models, including several of those used by the I... more The current state-of-the-art general circulation models, including several of those used by the IPCC, show considerable biases in the simulated present day high-latitude climate compared to observations and reanalysis data. These biases are most pronounced during the winter season. We here employ ideal vertical profiles of temperature and wind from turbulence-resolving simulations to perform a priori studies of the first-order eddy-viscosity closure scheme employed in the ARPEGE/IFS model. This reveals that the coarse vertical resolution (31 layers) of the model cannot be expected to realistically resolve the Arctic stable boundary layer. The curvature of the Arctic inversion and thus also the vertical turbulent-exchange processes cannot be reproduced by the coarse vertical mesh employed. To investigate how turbulent vertical exchange processes in the Arctic boundary layer are represented by the model parameterization, a simulation with high vertical resolution (90 layers in total) in the lower troposphere is performed. Results from the model simulations are validated against data from the ERA-40 reanalysis. The dependence of the surface air temperature on surface winds, surface energy fluxes, free atmosphere stability and boundary layer height is investigated. The coarse-resolution run reveals considerable biases in these parameters, and in their physical relations to surface air temperature. In the simulation with fine vertical resolution, these biases are clearly reduced. The physical relation between governing parameters for the vertical turbulent-exchange processes improves in comparison with ERA-40 data.
Boundary-Layer Meteorology, 2007
Large-eddy simulation (LES) is a well-established numerical technique, which resolves the most en... more Large-eddy simulation (LES) is a well-established numerical technique, which resolves the most energetic turbulent fluctuations in the planetary boundary layers. Averaging these fluctuations, high-quality profiles of mean values and turbulence statistics can be obtained in experiments with well-defined initial and boundary conditions. Hence, the LES data can be beneficial for assessment and optimization of turbulence closure schemes. A database of 80 LES runs (DATABASE64) for neutral and stably stratified planetary boundary layers (PBLs) is applied in this study to optimize the first-order turbulence closure (FOC). Approximations for the mixing length scale and stability correction functions have been tuned to minimise a relative root-mean square error over the entire DATABASE64. New stability functions have correct asymptotes describing regimes of strong and weak mixing found in theoretical exercises, atmospheric data and LES. The correct asymptotes exclude the need for a critical Richardson number in the FOC formulation. Further, we analysed the FOC quality as functions of the integral PBL stability and the vertical model resolution. We show that the FOC is never perfect because the turbulence in the upper half of the PBL is not generated by the local gradients. Accordingly, the parameterized and LES fluxes decorrelate in the upper PBL. With this imperfection in mind, we show that there is no systematic quality deterioration of the FOC in strongly stable PBLs provided the vertical model resolution is better than 10 levels within the PBL. In Running head: LES Application to Optimization of First-Order Closures Article type: The submission to a special issue of the "Boundary-Layer Meteorology" devoted to the NATO advanced research workshop "Atmospheric Boundary Layers: Modelling and Applications for Environmental Security"
Cyclones of the Arctic: definitions, pattern and regional trends
Cyclones are essential players in the high latitude climate system, as they transfer heat and moi... more Cyclones are essential players in the high latitude climate system, as they transfer heat and moisture into high latitudes. Through their impacts on precipitation patterns and sea ice, cyclones play a significant role in modulating the freshwater budget in the Arctic. To elucidate the mechanisms of synoptic impact on the high latitude climate we analyze cyclone activity trends and compare
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Papers by Øyvind Byrkjedal