Large eddy simulation (LES) of wind-driven circulation in a peri-alpine lake: Detection of turbulent structures and implications of a complex surrounding orography
Autor: | Vincenzo Armenio, Giulia Zanier, Marco Toffolon, Marco Antonio Santo, Lorenzo Giovannini |
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Rok vydání: | 2017 |
Předmět: |
010504 meteorology & atmospheric sciences
Wind stress Stratification (water) Orography Thermal wind Internal wave Oceanography Atmospheric sciences 01 natural sciences Physics::Geophysics 010305 fluids & plasmas Boundary layer Geophysics Space and Planetary Science Geochemistry and Petrology Downwelling Climatology 0103 physical sciences Earth and Planetary Sciences (miscellaneous) Physics::Atmospheric and Oceanic Physics Geology 0105 earth and related environmental sciences Large eddy simulation |
Zdroj: | Journal of Geophysical Research: Oceans. 122:4704-4722 |
ISSN: | 2169-9275 |
DOI: | 10.1002/2016jc012284 |
Popis: | We investigate wind-driven circulation in a peri-alpine lake (Lake Ledro - Italy) using LES-COAST. Lake Ledro is interesting because its own dimensions are suited for LES and it is surrounded by complex orography, affecting wind distribution. We consider the winter condition when stratification is nearly absent. Two types of time-varying wind stress are used: spatially homogeneous and spatially inhomogeneous respectively. The analysis of the eddy viscosities shows substantial differences with respect to the ocean case characterized by absence of coastal boundaries and homogeneous, steady wind. The quantities exhibit a noticeable inhomogeneous behavior: the horizontal eddy viscosity is larger in the water body far from the boundaries, whereas the vertical one is larger close to the lateral boundaries due to the presence of a boundary layer. The energetic bottom boundary layer, typically occurring in lakes, is not present. This because of the intrinsic unsteadiness of the thermal wind blowing over the lake and due to the absence of large amplitude internal waves, the latter present only in case of stable stratification. In the inhomogeneous wind case, up-welling and down-welling areas are not confined along the shoreline only, but are also generated in the water body due to substantial horizontal velocity divergence, and turbulent mixing, quantified by eddy viscosities, TKE and its dissipation rate, appears enhanced with respect to the homogeneous wind case. Finally, downwelling/upwelling areas along the windward/leeward coastline respectively were observed, whose quantitative estimation may give explanation for the bloom of cyanobacteria at the lake surface observed in winter. |
Databáze: | OpenAIRE |
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