Meteorology Flashcards
What meteorological input is needed?
Boundary layer meteorology: Process understanding, Turbulence wind profile and icing.
Forecast meteorology: How much will the turbine produce? To what certainty do we know that?
Climatology: What is the wind climate at a specific site? To what certainty can we expect a certain wind?
What does the eddy cacade cause?
Leads to logarithmic wind profile. The more mixing the more surface friction is felt.
What happens to the eddies at the top of the boundary layer?
The size of the eddies become smaller.
What happens to eddies during the night?
Surface cooling prevents mixing, and the depth of the turbulent (the layer with eddies) becomes shallow.
What is the effect of surface heating?
In neutral conditions the temperature gradient does not influence the turbulence. In unstable conditions the temperature gradient enhances turbulence. This alters the wind profile. In stable conditions the temperature gradient dampens turbulence. This also alters the wind profile. The degree of diabatic effects is controlled bu the dimensionless ratio z/L where L is the Obukhov length scale
What is the effect of stratifiation for stable, neutral and unstable conditions?
Stable (Night): High wind shear, Significant wind turning with height, lower roughness length
Neutral: Maximum roughness, High turbulence intensity
Unstable (Day): High turbulence intensity, Lower wind shear.
What are the two main tracks when modelling wind?
Prognostic non-linear models and linearized models.
What are the meteorological models used for wind?
Global circulation models - global forcast models with a resolution of ca 100km.
High resolution limited area models - local forcast model with resolution of ca 10-50 km.
Mesoscale models - higher order closure models - good resolution of boundary layer and a horizontal resolution of 0.1-10 km. Most important for wind energy.
What are the micro-scale models used and what are they used for?
Used for site specific calculations. Does not model weather processes. Purely flow models. Majority of non-linear microscale models does not include atmospheric stratification.
Large-eddy simulation (LES) models - resolves the larger scales of turbulence, parameterizes the smaller scales. Time resolved.
Raynolds Averaged Navier-Stokes (RANS) models - Similar to LES, but gives on time averaged fields. Only time average.
Explain linearized models.
Micro-scale models, used for site specific calculation. Does not model weather processes. Purely flow models. But compared to the non-linear models they run much faster. Can run on laptops
