Boundary layer characteristics and turbulent exchange mechanisms in highly complex terrain |
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| Authors: | Mathias W Rotach Marco Andretta Pierluigi Calanca Andreas P Weigel Alexandra Weiss |
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| Institution: | (1) Federal Office for Meteorology and Climatology, MeteoSwiss, Zurich, Switzerland;(2) Department for the Environment, Canton Ticino, Bellinzona, Switzerland;(3) ART Reckenholz, Zürich, Switzerland;(4) British Antarctic Survey, Cambridge, UK |
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| Abstract: | The Mesoscale Alpine Programme’s Riviera project investigated the turbulence structure and related exchange processes in an
Alpine valley by combining a detailed experimental campaign with high-resolution numerical modelling. The present contribution
reviews published material on the Riviera Valley’s boundary layer structure and discusses new material on the near-surface
turbulence structure. The general conclusion of the project is that despite the large spatial variability of turbulence characteristics
and the crucial influence of topography at all scales, the physical processes can accurately be understood and modelled. Nevertheless,
many of the “text book characteristics” like the interaction between the valley and slope wind systems or the erosion of the
nocturnal valley inversion need reconsideration, at least for small non-ideal valleys like the Riviera Valley. The project
has identified new areas of research such as post-processing methods for turbulence variables in complex terrain and new approaches
for the surface energy balance when advection is non-negligible. The exchange of moisture and heat between the valley atmosphere
and the free troposphere is dominated by local “secondary” circulations due to the curvature of the valley axis. Because many
curved valleys exist, and operational models still have rather poor resolution, parameterization of these processes may be
required. |
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| Keywords: | MAP complex terrain boundary layer valley wind slope wind turbulent exchange high-resolution numerical modeling turbulence parameterisation |
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