Long-term aerosol transport patterns in the southern hemisphere as observed by TOMS

Robert J. Swap

A majority of biomass burning can be attributed directly or indirectly to human activities and their effects on landscape-scale processes. For this reason, emissions from biomass burning and the impacts of these emissions on radiative and biogeochemical processes of ecosystems within and downwind of regions of burning have been topics of intense research.  Observations of atmospheric transports associated with aerosol and trace gases from biomass burning and industrial emissions and resultant empirical constructs used in this paper originate from the Southern African Fire-Atmosphere Research Initiative (SAFARI-92) and its follow on activity, the Southern African Regional Science Initiative (SAFARI 2000). Today it is possible to use empirical constructs developed during these intensive in-situ field campaigns in conjunction with remotely sensed observations.  With better sensors and, now, longer time records can be examined to look for patterns and trends in aerosol distributions over regions of biomass burning.

The presentation is focused on the major southern hemisphere continent where the majority of this biomass burning occurs – Africa. Twenty-five years of TOMS-AI data over southern Africa are analyzed using GIS-derived spatial characteristics of aerosol distributions coupled with mixed discriminant analysis / decision rule routines.  Observed daily aerosol observations are classified and the dominance of various prevalent aerosol distribution patterns determined during the May to October southern hemisphere dry season. Systematic changes in the distributions of the spatial and temporal patterns of aerosols over a given region as they vary with shifts in the El Nino-Southern Oscillation (ENSO) are found for the sub-continental region. Consistent trends in the frequency of occurrence over time of these patterns were also found that are consistent with others’ observations of global dimming and brightening over continental areas.

Our findings suggest a hemispherical response in aerosol distributions that varies according to the phase of the ENSO and therefore may have implications for regional scale radiation and biogeochemical balances.