OMI and MODIS observations of the anomalous 2008–2009 Southern Hemisphere biomass burning seasons

摘要

Significant inter-annual variability of biomass burning was observed inSouth America over the 2007–2009 period. The 2007 number of fires detectedfrom space in South America, as well as the magnitude of the atmosphericaerosol load resulting from fire activity, was the largest over the last tenyears. The huge 2007 increase in fire activity was followed by largereductions in the 2008 and 2009 burning seasons. Large drops of theatmospheric load of carbonaceous aerosols over the subcontinent, relative toprevious years, was registered in 2008 and 2009 by the OMI sensor onboardthe Aura platform, and the MODIS sensors on the Terra and Aqua satellites.The 2009 fire season in South America was the least active of the last tenyears. Satellite observations of fire statistics, precipitation, and aerosoloptical depth data were used to analyze the fire season over South Americaand Central Africa during the last ten years to understand the factors thatled to the 2007 and 2009 extremes. An analysis of precipitation anomaly datashows that the largest 6-month (May–October) precipitation deficit of thelast ten years in South America occurred during 2007. The same analysisindicates that in 2009, this region experienced the largest excessprecipitation of the decade. Since precipitation is the most importantmeteorological factor controlling biomass burning activity, it can beconcluded that the 2007 maximum and 2009 minimum in fire activity andaerosol load were driven by the observed levels of precipitation. Analysisof the precipitation record, however, does not explain the extremely low2008 biomass burning activity. Although the 2008 precipitation deficit wassimilar in magnitude to the one that in 2005 contributed to the second mostintense biomass burning season in the last ten years, the 2008 fire seasonwas surprisingly weak. The combined analysis of satellite data onatmospheric aerosol load, fire counts and precipitation strongly suggeststhat the observed 2008 decline in aerosol load and fire activity in SouthAmerica was heavily influenced by conditions other than meteorological factors.