Scales of response of the convective boundary layer to land-surface heterogeneity

The convective boundary layer (CBL) over domains with meso-gamma-scale (2-2 0 km) heterogeneity is characterized by preferentially located, organized r olls of characteristic size equivalent to the length-scale of the heterogen eity. Additionally, random turbulent thermals also develop when the length- scale of the heterogeneity exceeds 5-10 km. This is due to a complex intera ction between the horizontal pressure gradient generated by the heterogenei ty and the buoyancy forcing. Consequently, the corresponding wavelet spectr um exhibits two peaks - one representing the turbulent thermals at a charac teristic scale of about 1.5 times the CBL height and another denoting the o rganized eddies at a scale similar: to that of the heterogeneity. This impl ies that subgrid-scale parameterizations in models with grid size larger th an 5-10 km, which account only for random turbulence, are inadequate for he terogeneous domains. Also, this study may provide a more objective classifi cation of scales of atmospheric processes.