Roughness in Wind Atlas modelling
Roughness in the AROME high-resolution modelIn AROME, roughness is represented as the area-weighted grid average. AROME has four main land cover classes: sea, lake, nature and town. The Charnook formula is used to calculate roughnesses for sea and lake. This approximation takes into account the effects of wind to wave height and thus also the effects on roughness length. For ice covered sea/lake, the roughness is constant at z0ice=10-3 m.
Nature includes 12 different vegetation types (see Table 1), called ISBA (Interaction between Soil Biosphere and Atmosphere). For most of these vegetation types, the roughness depends on: 1) LAI = Leaf Area Index, which is a climatological value that changes during the year; and 2) HT = Height of Trees, which varies from 30 m at the equator to 15 m in the temperate zone and up to 2 m at high latitudes.
AROME has nine different town types, but only one of these types is found in Finland. The roughness for this suburban type is constant at z0town=1 m.
Table 1. Roughness length for each ISBA vegetation type in AROME.
Roughness in WAsP modellingFor WAsP modelling we used the CORINE land cover 2000 map, published in 2004. This map, created by Finland's environmental administration (SYKE), includes land cover information in 25 x 25 metre resolution for the whole of Finland.
We determined aerodynamic roughnesses for each land cover type separately. These roughness values are based on the literature and are shown in Table 2.
Table 2. Roughness length for each CORINE land use type.