A rose analysis method relating air chemistry to fire distribution in tropical Africa

Emissions from vegetation fires in the tropics contribute significantly to atmospheric chemistry at continental and global scales, Africa is the conti nent where the largest number of vegetation fires annually occurs. The use of Global Area Coverage (GAC) data, from the Advanced Very High Resolution Radiometer (AVHRR) sensor onboard the NOAA satellites, allows a good descri ption at continental level of the spatial distribution of intense active fi re patterns and a unique temporal perspective over multi-annual periods of time. In this study, 5 years of active fire maps, from November 1984 to Oct ober 1989, derived from GAC data for the African continent were considered. In order to enhance the relationships between spatially distributed phenom ena, such as regional patterns of active fires, and point data, such as exp erimental sites of atmospheric chemistry measurements, the rose diagram tec hnique as derived from directional statistics was exploited. This methodolo gical approach allowed the spatial characteristics of vegetation fires, whi ch is considered the main source of atmospheric pollutants in Africa, to be described using measures of frequency and distance for each reference poin t. Comparison between rose diagrams of fires and nitrate (NO;) content in p recipitation as measured at Enyele (Congo), at the heart of the equatorial forest during both dry and wet seasons, confirmed the usefulness of satelli te observations and the spatial analysis technique proposed. (C) 1999 Elsev ier Science B.V. All rights reserved.