Johan Arnqvist

Complex terrain experiments in the New European Wind Atlas

The New European Wind Atlas project will create a freely accessible wind atlas covering Europe and Turkey, develop the model chain to create the atlas and perform a series of experiments on flow in many different kinds of complex terrain to validate the models. This paper describes the experiments of which some are nearly completed while others are in the planning stage. All experiments focus on the flow properties that are relevant for wind turbines, so the main focus is the mean flow and the turbulence at heights between 40 and 300 m. Also extreme winds, wind shear and veer, and diurnal and seasonal variations of the wind are of interest. Common to all the experiments is the use of Doppler lidar systems to supplement and in some cases replace completely meteorological towers. Many of the lidars will be equipped with scan heads that will allow for arbitrary scan patterns by several synchronized systems. Two pilot experiments, one in Portugal and one in Germany, show the value of using multiple synchronized, scanning lidar, both in terms of the accuracy of the measurements and the atmospheric physical processes that can be studied. The experimental data will be used for validation of atmospheric flow models and will by the end of the project be freely available. This article is part of the themed issue ‘Wind energy in complex terrains’.

Meso-scale modeling of a forested landscape

Meso-scale models are increasingly used for estimating wind resources for wind turbine siting. In this study, we investigate how the Weather Research and Forecasting (WRF) model performs using standard model settings in two different planetary boundary layer schemes for a forested landscape and how this performance is changed when enhancing the roughness by a factor four in one of the schemes. The model simulations were evaluated using data from a 138 m tall mast in southeastern Sweden, where an experiment with six sonic anemometers and standard meteorological instrumentation was performed 2010-2012. The land cover around the mast is dominated by forest and for the most common wind direction, the forest extends more than 200 km from the mast. The two low-roughness simulations showed differences both in terms of estimated wind resource and wind shear. The simulation with enhanced roughness results in an improved correlation with measured data for near-neutral situations in the observed height range, whereas the correlation is deteriorated relative to the standard setup for stable atmospheric stratifications for heights above approximately 80 m. The inclusion of the displacement height in the post-processing of the results is also discussed.

Microscale model comparison (benchmark) at the moderate complex forested site Ryningsnäs

complex forested site Ryningsnäs Stefan Ivanell1, Johan Arnqvist1, Matias Avila2, Dalibor Cavar3, Roberto Aurelio Chavez-Arroyo4, Hugo Olivares-Espinosa1, Carlos Peralta5, Jamal Adib5, and Björn Witha6 1Uppsala University, Wind Energy Section, Campus Gotland, 621 67 Visby, Sweden 2Barcelona Supercomputing Center, BSC, Spain 3Wind Energy Department, Technical University of Denmark, Denmark 4National Renewable Energy Centre (CENER), Spain 5Wobben Research and Development MS GmbH, Germany 6ForWind Carl von Ossietzky Universität Oldenburg, Germany Correspondence to: Stefan Ivanell (stefan.ivanell@geo.uu.se)

A spectral model of stably stratified surface-layer turbulence

A new model to determine the spectral velocity tensor in a stably stratified flow is proposed. This model is complementary to the Mann model as it solves the stratified inviscid Rapid Distortion Th ...