Evaluating the RAMS to represent the Stable Boundary Layer in the South America Pampa

Data from a comprehensive field study in the south of Brazil are used to investigate stable boundary layer (SBL) structure in a near homogenous surface and to evaluate wind and temperature fields, stable boundary layer height, and surface sensible and heat fluxes as predicted by the mesoscale model RAMS. Current parameterizations of surface and boundary layers processes in RAMS are based on scaling laws strictly valid only for flat topography and uniform land cover. In order to investigate these limits of applicability of RAMS, to describe the SBL, simultaneous observations were carried out in two sites characterized by different land surface in a region of topography not homogeneous. Eight nights with clear-skies and different synoptic winds were selected from the field campaign. The surface wind and temperature time evolutions are well described by the mesoscale model for both sites. However the latent and sensible heat fluxes calculated with the eddy covariance methods are overestimated by the model. It is investigated if the scatter between observed and simulated sensible turbulent fluxes is due to sub-grid scale effects related to local topography as well as the scatter in the latent heat fluxes are due to soil humidity.