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Volume 16, issue 12
Atmos. Chem. Phys., 16, 8009-8021, 2016
https://doi.org/10.5194/acp-16-8009-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: The Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST)...

Atmos. Chem. Phys., 16, 8009-8021, 2016
https://doi.org/10.5194/acp-16-8009-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Jul 2016

Research article | 01 Jul 2016

A study of local turbulence and anisotropy during the afternoon and evening transition with an unmanned aerial system and mesoscale simulation

Astrid Lampert1, Falk Pätzold1, Maria Antonia Jiménez2, Lennart Lobitz1, Sabrina Martin3, Gerald Lohmann4, Guylaine Canut5, Dominique Legain5, Jens Bange6, Dani Martínez-Villagrasa2, and Joan Cuxart2 Astrid Lampert et al.
  • 1Institute of Flight Guidance, TU Braunschweig, Braunschweig, Germany
  • 2Universitat de les Illes Balears, Palma de Mallorca, Spain
  • 3Climatology and Environmental Meteorology, Institute of Geoecology, TU Braunschweig, Braunschweig, Germany
  • 4Energy Meteorology Group, Institute of Physics, Oldenburg University, Oldenburg, Germany
  • 5CNRM-GAME, UMR3589, Météo-France and CNRS, Toulouse, France
  • 6Eberhard Karls University Tübingen, Tübingen, Germany

Abstract. Observations of turbulence are analysed for the afternoon and evening transition (AET) during the Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST) experimental field campaign that took place in Lannemezan (foothills of the Pyrenees) in summer 2011. The case of 2 July is further studied because the turbulence properties of the lower atmosphere (up to 300m above ground level) were sampled with the Meteorological Mini Aerial Vehicle (M2AV) from turbulently mixed to stably stratified atmospheric conditions. Additionally, data from radiosoundings, 60m tower and UHF wind profiler were taken together with the model results from a high-resolution mesoscale simulation of this case. Weak large-scale winds and clear-sky conditions were present on the studied AET case favouring the development of slope winds and mountain–plain circulations. It is found that during the AET the anisotropy of the turbulent eddies increases as the vertical motions are damped due to the stably stratified conditions. This effect is enhanced by the formation of a low-level jet after sunset. Finally, the comparison of the anisotropy ratio computed from the different sources of observations allow us to determine the most relevant scales of the motion during the AET in such a complex terrain region.

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For a large field experiment in summer 2011 in southern France (BLLAST campaign), the development of turbulence in the atmosphere was analysed during the afternoon and evening. Besides ground-based remote sensing and in situ observations, turbulence parameters were measured with an unmanned aerial vehicle and analysed by numerical simulation. Turbulence decreased during the afternoon, but increased after sunset due to local wind systems. Turbulent eddies lost symmetry during the transition.
For a large field experiment in summer 2011 in southern France (BLLAST campaign), the...
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