ИСТИНА

Lakes may be a source or sink of sensible heat and often are a source of moisture for the atmosphere. Lake surfaces are aerodynamically much smoother than vegetated land surfaces, which contribute to large variations of fluxes of momentum, heat, moisture and gases between the land and the atmosphere. Formulations of estimates of lake-atmosphere fluxes are often taken from experimental studies conducted in oceans or in lakes where the wind sheltering and mesoscale turbulence effects are not significant. The same coefficients values are most likely not applicable to all lake environments, especially over small lakes with different sheltering characteristics. Over complex terrain the turbulence is generically inhomogeneous due to both thermal (radiative) and dynamic forcing. This inhomogeneity leads to meso-scale and even sub-meso-scale flows and waves. It is argued here that these (sub) meso-scale motions can significantly contribute to the vertical structure of the boundary layer and hence vertical exchange of heat and mass between the surface and the atmosphere. Accuracy and variability of transfer coefficients for air-water momentum, heat, moisture and trace gases is currently difficult to determine and any bias in them will influence flux estimates. The turbulent exchange of heat and momentum were measured above Verkhnee lake (White sea region) using the eddy covariance method in winter season. Measurements of small-scale turbulence made in the atmospheric surface layer at the various sites above the ice cover are used to describe the structure of turbulence in wind flows above complex terrain. Turbulent data were continuously measured with 3-component and 2-component sonic anemometers during 7-day field campaign. These measurements allowed to study temporal and spatial structure of wind flow in detail, and herein we report turbulence statistics (e.g., fluxes, variances, spectra, and co-spectra) and their variations in flow above small lake surrounded by the forest. High-frequency observations also were used to examine the relative contributions of wind shear (u*) and convection (w*) to turbulence in the surface mixed layer.