BISAC SCI019000 Earth Sciences / General
The paper presents the quantitative assessment of the hydrodynamic parameters of the convectively mixed layer (CML) arising in ice-covered boreal lakes as a result of non- homogeneous heating of the water column. The study is focused on revealing the features of CML spatial structure and calculating all six elements of the turbulent stress matrix. The main feature of the experimental technique is application of two rigidly coupled acoustic current profilers (ADCP) installed on ice and operating in the asynchronous measurement mode. In the case of down-looking axes of both devices, their positions relative to each other were chosen so that one or two pairs of beams intersected at a certain depth. Due to this configuration, it was possible to perform a rigorous calculation of all turbulent stresses based on the data obtained from all six beams. The intensities of pulsations were estimated along all three axes, complete with error analysis. A high degree of anisotropy of the pulsations and a periodic nature of its change over time were detected. An analysis of the dynamics of average velocities carried out for depths of up to 2.87 m with discreteness of 2.5 cm (for CML thickness of 3–6 m) revealed the presence of quasi-deterministic convective cells. In the horizontal plane, a systematic “drift” was found, due to the presence of large-scale geostrophic circulation. The presence of such a drift made it possible, as a first approximation, to convert the experimentally obtained Eulerian characteristics into Lagrangian ones and, accordingly, draw conclusions about the spatial structure of the cells. In particular, based on the analysis of progressive vector diagrams in vertical planes, the depth ranges were determined at which the zones of up- or downwelling prevailed. The distribution of these zones is of great importance in studying the spatial dynamics of plankton. KEYWORDS: Boreal lakes; under-ice radiation; convectively mixed layer; acoustic Doppler current profilers; quasi-deterministic structures; progressive vector diagrams; up- and downwelling zones; turbulent stresses.
Boreal lakes; under-ice radiation; convectively mixed layer; acoustic Doppler current profilers; quasi-deterministic structures; progressive vector diagrams; up- and downwelling zones; turbulent stresses.
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