  In this paper non-neutral approaching flows were employed in a meteorological
wind tunnel on a regular urban-like array of rectangular buildings. As far as
stable stratification is concerned, results on the flow above and inside the
canopy show a clear reduction of the Reynolds stresses and an increment of the
Monin-Obukhov length up to 80%. The roughness length and displacement height
were also affected, with a reduction up to 35% for the former and an increment
up to 12% for the latter. A clear reduction of the turbulence within the canopy
was observed. In the convective stratification cases, the friction velocity
appears increased by both the effect of roughness and unstable stratification.
The increased roughness causes a reduction in the surface stratification,
reflected in an increase of the Monin-Obukhov length, which is double over the
array compared to the approaching flow. The effect on the aerodynamic roughness
length and displacement height are specular to the SBL case, an increase up to
50% of the former and a reduction of the same amount for the latter.
