Improved parametrization of the boundary layer in Harmonie- Arome (focusing on low clouds)

With the introduction of the HARATU turbulence scheme (Lenderink & Holtslag 2004, de Rooy 2014, Bengtsson 2017) in cycle 38, Harmonie-Arome improved on several output parameters, especially 10m wind speed. From the moment HARATU is included at KNMI (in 2015), Harmonie-Arome clearly and consistently outperforms wind speed forecasts of Hirlam, ECMWF and Harmonie-Arome with CBR turbulence. However, from cy38 onwards, the model underestimates low clouds and overestimates the cloud base height of low clouds, both crucial for e.g. aviation purposes. Within the Hirlam consortium this problem is considered as the most important deficiency of Harmonie-Arome.