The Amazon Boundary Layer Experiment: Wet season 1987

Abstract

The Amazon Boundary Layer Experiment (ABLE 2B) used data from aircraft, ground‐based, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over the Amazon Basin during wet season (April–May 1987) conditions. This paper reports the experimental design for ABLE 2B and a brief summary of the results for the combined ABLE 2A and ABLE 2B. The detailed results of ABLE 2B are presented in a series of papers in this issue. The chemical composition of the atmospheric mixed layer over the Amazon Basin ecosystem during both wet and dry seasons reflects interacting influences from biogenic gas and aerosol sources and sinks, photochemistry, exchange with the free troposphere, influx of marine air from the tropical Atlantic, and long‐range transport of pollutants from distant industrial and agricultural activities. The signature of human activities on undisturbed regions of the Amazon Basin is most pronounced during the dry season due to meteorological conditions which favor the transport to and accumulation of regional pollution from biomass burning in the troposphere over the region. During the wet season, the northern hemisphere becomes a source of pollution to the Amazon as a result of episodic inputs associated with changes in the large‐scale atmospheric circulations associated with subtropical anticyclones. Seasonal variations in biogenic emissions are important in determining the photochemical characteristics of the Amazon mixed layer. The undisturbed regions of the Amazon are potentially a globally significant sink for ozone during wet‐season conditions. The region is an important source of both methane and nitrous oxide. The extensive area of undisturbed tropical forests in the Amazon Basin and the relatively pristine atmospheric chemical conditions during much of the wet season are an important resource for understanding the role of biosphere‐atmosphere interactions in global atmospheric chemistry.