Agricultural and Forest Meteorology 109 (2001) 135–141 Diurnal cycle of temperature and wind fluctuations within an African equatorial rain forest C. Bouka Biona a,∗ , A. Druilhet b , B. Benech b , R. Lyra c a Laboratoire de Physique de l’Atmosphère, Université Marien Ngouabi, BP 69, Brazzaville, Congo b Laboratoire d’Aérologie, Université Paul Sabatier, 31062 Toulouse Cedex, France c Universidade Federal de Alagoas, Maceio, Brazil Received 9 July 1999; received in revised form 24 April 2001; accepted 3 May 2001 Abstract This paper describes the characteristics of the temperature and wind speed fluctuations measurements inside the north Congo forest during the DECAFE experiment in February 1988. The temperature spectra show a maximum at 0.018 Hz with a slope close to - 2 3 and the scattering increases as the frequency decreases while the nS(n) wind speed spectra has a maximum at 0.02 Hz with a negative slope at higher frequencies. The dynamical or thermal turbulence in the canopy layer is characterized by a maximum variance in the middle of the day and by two singularities during the transition time at sunrise and sunset when variances are small. This behavior could be due to the turbulent kinetic energy which increases turbulence in the upper part of the canopy layer and also to strongly anisotropic motions generated by the non-homogeneity of the temperature and wind fields inside the forest. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Forest canopy; Fluctuations; Variance; Turbulence; Spectra 1. Introduction One of the main objectives of the DECAFE (Dynamique Et Chimie de l’Atmosphère en Forêt Equatoriale) experiment was to characterize ex- changes of gases of climatic interest (ozone, carbon dioxide, methane, NO X , etc.) between the dense rain forest and the free atmosphere during the dry sea- son via the surface layer (SL: first 100 m above the crown canopy) and the mixed layer situated above the SL. Several methods have been used to study these exchanges. These have been done by analyzing the ∗ Corresponding author. Tel.: +242-66-42-65; fax: +242-81-01-41. E-mail address: cbbouka@hotmail.com (C. Bouka Biona). data profiles or direct measurements of fluxes of the quantities of interest through the diurnal cycle. But in the canopy layer, some of these quantities and/or their gradients are very small, even zero. During ABLE 2A, a dry season experiment in the Amazonian forest (Brazil), Wofsy et al. (1988) re- ported in their work that their CO 2 measurements did not show a monotonic increase of concentration in the evening in spite of the well developed hydrostatic stability in the canopy layer. Measurements made by Kaplan et al. (1988) during the same experiment showed an increase of the ozone concentration in- side the forest while its principal source is neither in the canopy layer nor in the soil. For the experiment carried out at the same site during the wet season, Fitzjarrald et al. (1990) and Fitzjarrald and Moore 0168-1923/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0168-1923(01)00253-2