Impact of turbulence closures on diurnal temperature evolution for clear sky situations over Belgium

The aim of this study is to quantify the impact of turbulence closure on the simulation of surface air temperature at screen height (1.5 m) over Belgium. The mesoscale model MAR (Modele Atmospherique Regional), developed at the Universite catholique de Louvain, is used to examine one-dimensional situations. A new second-order closure (level 2.5) is implemented containing prognostic equations for all three velocity variances, and diagnostic or prognostic formulations for the dissipation. This closure is compared with first and one-and-a-half order closures. Idealized nearly-neutral and convective cases underline the differences between first and second-order closures, and between diagnostic and prognostic equations for the dissipation. The one-and-a-half and second-order closures give satisfying results, but the first-order closure produces generally less appropriate vertical diffusion. Observed clear sky and weak horizontal advection situations have shown the sensitivity of 24 h temperature evolution to the choice of the turbulent closure.