MEAN AND TURBULENT STRUCTURE OF NONHOMOGENEOUS BOUNDARY-LAYER - EXPERIMENTAL-STUDY OF 2 LOCAL WINDS DURING AUTAN-84

The ''Autan 84'' experiment was conducted in order to analyse the char acteristics of the Atmospheric Boundary Layer (ABL), in conditions whe re orographic effects on flow are of importance. The results presented here concern two situations of local winds, driven by the orography: a southeast boundary layer flow (''Autan'' wind), and a north-northwes t boundary layer flow (''Tramontane'' wind). On horizontal areas of 10 (3)-10(4) km2, mean wind, temperature and humidity showed important va riations, from which were calculated divergence, vorticity, mean verti cal velocity and advection terms. The heat budget in the ABL was also established. In the two cases, we calculated the extent to which the s urface available energy (sensible heat flux) was converted into either boundary layer heating or into the counterbalancing advection of cold air. Moreover, the turbulence structure showed important differences between the two situations, even though global stabilities were closel y related: in the Autan case, spectra and cospectra showed length scal es one order of magnitude greater than the thickness of the boundary l ayer, perhaps due to dynamic organization in the boundary layer.