Modelling of Wind Atlas

The Wind Atlas of Finland is based on a combination of the Numerical Weather Prediction (NWP) model AROME and the statistical WAsP model that is commonly used in wind atlas applications. Both models are actively utilised at the Finnish Meteorological Institute (FMI).

NWP models, HIRLAM and AROME, are dynamical forecast models that describe atmospheric physics as accurately as possible for weather forecasting purposes. The statistical WAsP model modifies the wind time series produced by AROME in order to generate a climatological description of wind conditions. WAsP takes into account the effects of local roughness and topography.

The base material contains 48 months of weather model simulations where the winds and other variables are calculated for grid boxes 2.5 x 2.5 km2 in size. The results of the weather model are then post-processed for 250 x 250 m2 grid boxes in predefined areas by using the WAsP model.

In addition, the AROME model was used for simulating 24 extra months, 12 representing a year with strong winds and 12 representing a year with weak wind conditions. The Wind Atlas itself does not take these periods into account, although tables of dynamical map products present the results of the extra months as separate values. This data set is calculated only for 2.5 x 2.5 km2 grid boxes.

All the wind atlas periods were simulated by AROME in 6-hour sequences, storing the atmospheric state after 3 and 6 hours of simulation. The initial state of each 6-hour sub-period and the required boundary conditions were produced by using weather observations. The FMI's weather prediction model HIRLAM was used for this analysis process. The computational domain of HIRLAM covered Northern Europe, with grid spacing of 7.5 km. The data required at the edge of the HIRLAM model was taken from the ERA-Interim reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). ERA-Interim data cover the entire globe, with grid spacing of 80 km.

Wind information from 50 to 400 metres

The Wind Atlas includes monthly wind statistics and estimates of wind energy production (MWh) for three different windmill types (capacities of 1, 3 and 5 MW). These values are given for seven height levels: 50 m, 75 m, 100 m, 125 m, 150 m, 200 m and 400 m, and for a total of 63 550 points each representing an area of 2.5 x 2.5 km2. The mean wind speed is also given for grid boxes of 250 x 250 m2 for archipelago, fjeld and coastal regions as well as for selected land regions. These values are processed from wind information produced by AROME, using mesoscale Lib-software and the WAsP model.

The wind information shown in the Wind Atlas represents the mean monthly and annual wind conditions over the last 50 years. The wind conditions of an individual year may deviate considerably from the mean conditions. Furthermore, the actual wind conditions during the lifetime of a windmill may differ from the mean conditions presented in the Wind Atlas. The values of the Wind Atlas do not take the possible effect of climate change into account. However, this effect is described in other sections of the Wind Atlas manual.

The Finnish Wind Atlas is based on a combination of the FMI\'s mesoscale numerical weather prediction model AROME and statistical WAsP model that is commonly used in wind atlas applications.