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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 01 Mar 2019

Research article | 01 Mar 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Nocturnal boundary layer turbulence regimes analysis during the BLLAST campaign

Jesús Yus-Díez1,5, Mireia Udina1, Maria Rosa Soler1, Marie Lothon2, Erik Nilsson3, Joan Bech1, and Jielun Sun4 Jesús Yus-Díez et al.
  • 1Departament de Física Aplicada – Meteorologia, Universitat de Barcelona, C/Martí i Franquès, 1., 08028, Barcelona, Spain
  • 2Laboratoire d’Aérologie, University of Toulouse, CNRS, France
  • 3Department of Earth Sciences, Uppsala University, Uppsala, Sweden
  • 4NorthWest Research Associates, Boulder, Colorado, USA
  • 5Institute of Environmental Assessment and Water Research (IDAEA-CSIC), C/Jordi Girona 18–26, 08034, Barcelona, Spain

Abstract. A night-time turbulence regime classification, the so-called HOckey-Stick Transition (HOST) theory, proposed by Sun et al. (2012) from the Cooperative Atmosphere-Surface Exchange Study 1999 (CASES-99) is explored using data from the Boundary-Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign which took place during the summer 2011 in the north of the central French Pyrenean foothills.

Results show that the HOST turbulence relationships for the BLLAST field campaign data is strongly dependent on both the meteorological and orographic features. The HOST pattern only appears for nights when a stably stratified boundary layer can be developed, corresponding to fair weather and clear sky nights, when the flow is generated by the nearby orography, from the south and southeast directions. Those flows strongly influenced by the orography may generate intermittent or enhanced turbulence. When considering the whole dataset for these flow directions, several enhanced turbulence points are found to be associated with sudden wind speed and directional shear transitions. In contrast, flows from other directions do not reproduce the HOST relationship and the turbulence relationship is almost linear, independent of the vertical temperature gradients, corresponding to flows driven by mesoscale or synoptic scales. In addition we identify examples of gravity waves and top-down turbulent events that lead to transitions between the turbulence regimes.

Jesús Yus-Díez et al.
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Jesús Yus-Díez et al.
Jesús Yus-Díez et al.
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Short summary
This study helps to a better understanding of the turbulence description and the interactions occurring in the lower part of the boundary layer. The study is done in an orographically influenced site close to the Pyrenees to explore the HOST theory. For the studied site the HOST is seen to be strongly dependent on both the meteorological conditions and the orographic features. Examples of intermittent turbulence events that lead to transition between the turbulence regimes are also identified.
This study helps to a better understanding of the turbulence description and the interactions...