The objective of the Dynamique et Chimie de l'Atmosph¿re en Foreˆt Equatoriale (DECAFE) program is to determine the influence of African tropics on atmospheric chemistry. Savannas and forests constitute the main ecosystems in this area. Because of the occurrence of biomass burning during the dry season, savannas of the northern and southern hemispheres are active sources of many constituents which are of interest to atmospheric chemistry. The rain forest, with its important biomass activity is also a source or sink for gases and aerosols. Man's impact on this ecosystem is important since the rate of deforestation is about 0.5% per year. Furthermore, a general air motion from savanna regions toward the tropical rain forest is observable in most parts of Africa, leading to important interactions between the respective emissions of these two ecosystems. The DECAFE experiments presented in this issue were located in the Mayombe forest (southern Congo) and in the forest of the northern Congo. A study of rain chemistry was undertaken in 1986 in the Mayombe forest, then continued in the northern forest. In February 1988 a coordinated experiment was held in the tropical rain forest of the north, near Impfondo. The paper presents an overview of the general meteorological and climatological situation in the African tropics, a study of the climatological features of the sites, and a short description of the Impfondo experiment, which is the subject of most of the contributions to this special issue. The local meteorological situation during the time of the experiment is analyzed. ¿ American Geophysical Union 1992