Some typical cross-section patterns of the surface-based turbulent layer depicted by sodar echograms. The grey-scale intensity is proportional to the strength of the thermal optically active turbulence characterised by the structure refraction index parameter : a) very weak turbulence, 28/04/2012; b) weak turbulence, 26/05/2012; c) strong turbulence within the surface layer, 09/04/2012; d) turbulence in the surface layer and in elevated layers, 20/08/2012.