JOURNALOF GEOPHYSICAL RESEARCH, VOL. 97, NO. D6, PAGES 6123-6136, APRIL 30, 1992 THE DEGAFE EXPERIMENTS : OVERVIEW AND METEOROLOGY Jacques Fontan, Aim6 Druilhet, Bruno Benech, Roberto Lyra Laboratoire d'A6rologie, Universit6 Paul Sabatier, Toulouse, France Bernard Cros Laboratoire de Physique de 1 'Atmosphere, Universit6 de Brazzaville, Congo Abstract. The objective of the Dynamique et a large number of coordinated measurements from Chimie de l'Atmosph•re en For6t Equatoriale airborne, ground-based, and satellite platforms (DECAFE) program is to determine the influence of have substantiated the few previous studies of African tropics on atmospheric chemistry. biogenic emission and the concentration of Savannas and forests constitute the main atmospheric constituents such as nitric oxide ecosystems in this area. Because of the (Kaplan et al., 1988 ; Torres et al., 1988), occurrence of biomass burning during the dry isoprene (Zimmerman et al., 1988 ; Rasmussen et season, savannas of the northern and southern al., 1988), dimethyl sulfide (Andreae and hemispheres are active sources of many Andreae, 1988), etc. (see the special issue of constituents which are of interest to atmospheric Journal of Geophysical Research, 93 (D2), 1988). chemistry. The rain forest, with its important As the dry season progresses, biomass burning biomass activity is also a source or sink for becomes an important source of nitric oxide, gases and aerosols. Man's impact on this carbon monoxide, and hydrocarbon emissions, ecosystem is important since the rate of thereby leading to an increase in the deforestation is about 0.5% per year. concentration of ozone, as indicated by Furthermore, a general air motion from savanna measurements carried out in Amazonia (Crutzen et regions toward the tropical rain forest is al., 1985 ; Delany et al., 1985). By contrast, observable in most parts of Africa, leading to measurements over Africa are scarce. important interactions between the respective The aerosol has been studied by Cros et al. emissions of these two ecosystems. The DECAFE (1981), Clairac et al. (1988), Crozat et al. experiments presented in this issue were located (1973), Crozat (1978) ; its isotopic composition in the Mayombe forest (southern Congo) and in the in carbon by Cachier et al. (1985) ; the emission forest of the northen Congo. A study of rain of sulfur compounds by Delmas et al. (1978) and chemistry was undertaken in 1986 in the Mayombe (1980) and Delmas and Servant (1987). Desalmand forest, then continued in the northern forest. In et al. (1982) have shown the richness of the February 1988 a coordinated experiment was held environment in cloud condensation nuclei on the in the tropical rain forest of the north near Ivory Coast. Cros et al. (1987) and (1988) show Impfondo. The paper presents an overview of the that during most of the year, ozone general meteorological and climatological concentration is high for this area, confirming situation in the African tropics, a study of the the results obtained by Fishman et al. (1986) and climatological features of the sites, and a Fishman and Larsen (1987), via satellite short description of the Impfondo experiment, measurements. which is the subject of most of the contributions The Dynamique et Chimie de l'Atmosph•re en to this special issue. The local meteorological For6t Equatoriale (DECAFE) program was initiated situation during the time of the experiment is by the "Laboratoire de Physique de l'Atmosph•re" analyzed. of Brazzaville University and the "Laboratoire d'A6rologie" of Paul Sabatier University with the following objectives : (1) determination of the 1. Introduction sources and sinks of atmospheric constituents of interest to atmospheric chemistry and/or having Intertropical areas exert a great influence on an influence on the radiative budget of the global atmospheric chemistry. Tropical rain atmosphere. (2) study of the atmospheric forests, with strong biomass activity and savanna chemistry in the intertropical region of Africa with large scale annual burning of biomass, are and particularly over the rain forest where the intense sources/or sinks for gases and aerosols constituents produced by biomass burning in of atmospheric interest. Before 1985 a very savanna can react with biogenic emissions from limited number of measurements of btogenic the rain forest. Atmospheric chemistry depends on emissions had been conducted in tropical horizontal advection and vertical transfer of ecosystems (see the review by Seller and Conrad constituents and more generally on atmospheric (1987), Harris et al. (1988)). AmazonBoundary dynamics, cloud physics, and chemistry. An Layer Experiments (ABLE 2A and ABLE 2B) based on objective of the DECAFEprogram is therefore to study the dynamics of the lower atmosphere. This includes studies of the influence of the forest, Copyright 1992 by the American Geophysical Union. characterized by a very low Bowen ratio, the presence of the intertropical convergence zone Paper number 91JD02426. (ITCZ), namely, the boundary between the south 0148-0227/92/91JD-02426505.00 west monsoon flux and above a north, northeast 6123