The DECAFE experiments: Overview and meteorology

Abstract

The objective of the Dynamique et Chimie de l'Atmosphère en Forêt 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 northen 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.

Global geographical databases for modelling trace gas fluxes

“…1988, Crill et a/. 1988a, Devol et al 1988, Harriss et al 1988 Fontan et al 1992. The overall results from these missions confirm that tropical wetlands are larger sources of methane than early studies suggested.…”

Identification of Processes Driving Low-Level Westerlies in West Equatorial Africa

“…Broadly, the atmospheric circulation is dominated by a large seasonal shift in the position of the intertropical convergence zone (ITCZ), which is determined by the northeast and southwest trade winds, and the monsoon circulation from the Atlantic (Fontan et al 1992). Broadly, the atmospheric circulation is dominated by a large seasonal shift in the position of the intertropical convergence zone (ITCZ), which is determined by the northeast and southwest trade winds, and the monsoon circulation from the Atlantic (Fontan et al 1992).…”

“…In the lower troposphere, moist air from the Atlantic Ocean (Fontan et al 1992), known as low-level equatorial westerlies (Nicholson and Grist 2003), are associated with the southeasterly trades on the northeastern flank of the Saint Helena (South Atlantic) high. Because of Coriolis forces, the southeasterlies become westerlies when crossing the equator.…”

Large-scale overview of the summer monsoon over West Africa during the AMMA field experiment in 2006

“…Otherwise measurements during the dry season have been made around the Ivory Coast as part of TROPOZ (December 1987, January 1991 (Jonquieres et al, 1998) and DECAFE (January 1991) (Delmas et al, 1995), and from Niamey as part of AMMA DABEX (January and February 2006). Other measurements in Central and Southern Africa have also focussed on the dry season when there is widespread biomass burning Delmas et al, 1999;Fontan et al, 1992). Figure 28 shows the flight tracks of most of the AMMA 2006 monsoon chemistry flights made by the BAe-146, the DLR Falcon, the French Falcon and the M55 aircraft between 20 July and 21 August plotted as a function of latitude and altitude and coloured by the O 3 concentration.…”