HARATU

An improved turbulence scheme for Harmonie-Arome

Harmonie-Arome is the high resolution weather and climate model used, and partly developed, at KNMI. Although Harmonie has proven its value in operational practice, especially in cases of extreme weather, some deficiencies remain. A number of those deficiencies can be related to the representation of turbulence (vertical mixing) in the model (de Rooy, 2014). Implementation of a new turbulence scheme (Lenderink and Holtslag, 2004; van Meijgaard et al., 2012; Bengtsson et al. 2017) resulted in a large, benificial impact, not only on the known deficiencies but e.g. also on the wind speed predicitions (see Figure 1). Figure 1 shows that all models except Harmonie-Arome with the new turbulence scheme reveal a clear diurnal cycle in the wind speed bias.

HARATU
Model 10m wind speed bias determined using observations covering a large part of Europe. Shown are model results with; the previous turbulence scheme (CBR, black), the new HARATU turbulence scheme (red), as well as results with the ECMWF model (blue).