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Hi Rogier, thank you for the explanation. An interesting information is that WAsP knows, beyond its GUI, to calculate directly from geostrophic wind to local wind, without generalization. It means that for such calculation, no height and roughness classes are applied? This is what WindPRO uses in its time series calculation (the scaler)? Though I still struggle to fully understand the logic. I would expect that it would be sufficient do define the general wind climate for just one roughness and one height and the rest can be derived from it. And that the recalculation to different classes would be relatively simple, without need to store pre-calculated data, because this it is not site- and project- dependent. Am I wrong? The most confusing thing to me is that different general wind climatologies sometimes provide different wind shears. You write that if my input wind climate, height, location and stability for the generalization is the same and the wind climate at z0=0.1 and h=10 m is the same, all other heights and roughnesses should also be the same. This is expectable. But why this need not apply if the wind climate at z0=0.1 and h=10 m is the same, but the wind climate, height, location and stability for generalization are different? David

Dear WAsP team, I am a long-term user of WAsP, but, shamefully, there is one very fundamental feature of the model, which is not very clear to me. As I understand the principle of WAsP, the model generalizes the site specific wind data in a way that the effects of local roughness, orography, measurement height and possible obstacles are deducted from the data, so that only the information of "general" windiness is preserved. I would expect then, that the wind climatology for just one standard height and roughness length would be a full description of the generalized wind climate, because any other information is site specific and can be calculated from the general data and local properties. Even more, I would expect that the input wind data, at least the ones provided by .tab observed wind climatology files, cannot provide more information than for one general roughness and height, because the file contains no further information that would enable to distinguish between the classes (like the wind shear or stability perhaps could be). In spite of it, the classification of GWC in height and roughness classes is a prominent feature of WAsP application. Then my questions are: 1) Why are multiple height and roughness classes defined? 2) From where the information comes from, which makes the relations between wind parameters in different classes to be different in different wind atlases? For example, if the wind climatology for z0=0.1 and h=10m is the same in two GWCs, why it may differ in other height/stability classes? (May it?) 3) Could you advice some "rules of thumb", which circumstances and how do impact the differentiation as mentioned in 2) ? 4) Is there any literature describing this topic? With regards David Hanslian

Dear Duncan and WAsP team, thank you for the continual improvements of WAsP software. However, I have a problem with the new limitation in the actual release. Sometimes I need to use old wind atlas files that employ "classical" roughness classes of 0.00, 0.03, 0.1 and 0.4 m. But I found that now WAsP does not perform with these wind atlases at sites, where the reference roughness of any sector is higher than 0.4 m. In such cases the report appears: 'climate calculation: meso-scale roughness lies outside gwc roughness classes.' I suppose that this was announced with the new release as "Stricter calculation constraints for site lying outside wind atlas classes". For me it is a good point to be aware, when the calculation can be incorrect by this issue, but in some cases I do not have an option to avoid using old wind atlas. Would it be possible just to alert but not disable the calculation? How big errors would occur then? Are the new model versions more sensitive to this issue than the older ones? Or, if this change is definitive, could you advise me how approximately recalculate wind atlas files in order to add high roughness class? (other way than by using original map and wind climate) Thank you David