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Ann. Geophys., 21, 2119-2131, 2003
www.ann-geophys.net/21/2119/2003/
© European Geosciences Union 2003
Turbulent characteristics of a semiarid atmospheric surface layer from cup anemometers – effects of soil tillage treatment (Northern Spain)
S. Yahaya, J. P. Frangi, and D. C. Richard
Laboratoire Environnement and Développement, CP 7071 Université Denis Diderot (Paris 7), 2 Place Jussieu, 75251 Paris Cedex 05, France
Abstract. This paper deals with the
characteristics of turbulent flow over two agricultural plots with various
tillage treatments in a fallow, semiarid area (Central Aragon, Spain). The main
dynamic characteristics of the Atmospheric Surface Layer (ASL) measured over
the experimental site (friction velocity, roughness length, etc.), and energy
budget, have been presented previously (Frangi and Richard, 2000). The current
study is based on experimental measurements performed with cup anemometers
located in the vicinity of the ground at 5 different levels (from 0.25 to 4 m)
and sampled at 1 Hz. It reveals that the horizontal wind variance, the Eulerian
integral scales, the frequency range of turbulence and the turbulent kinetic
energy dissipation rate are affected by the surface roughness. In the vicinity
of the ground surface, the horizontal wind variance logarithmically increases
with height, directly in relation to the friction velocity and the roughness
length scale. It was found that the time integral scale (and subsequently the
length integral scale) increased with the surface roughness and decreased with
the anemometer height. These variations imply some shifts in the meteorological
spectral gap and some variations of the spectral peak length scale. The
turbulent energy dissipation rate, affected by the soil roughness, shows a
z-less stratification behaviour under stable conditions. In addition to the
characterization of the studied ASL, this paper intends to show which
turbulence characteristics, and under what conditions, are accessible through
the cup anemometer.
Key words. Meteorology and
atmospheric dynamics (climatology, turbulence, instruments and techniques)
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