Publication Date:
2013-05-21
Description:
[1] As a representative site of the southern African biomass-burning region, sun-sky data from the 15-year AERONET deployment at Mongu, Zambia was analyzed. For the biomass burning season months (July-November), we investigate seasonal trends in aerosol single scattering albedo (SSA), aerosol size distributions, and refractive indices from almucantar sky scan retrievals. The monthly mean single scattering albedo at 440 nm in Mongu was found to increase significantly from ~0.84 in July to ~0.93 in November (from 0.78 to 0.90 at 675 nm in these same months). There was no significant change in particle size, in either the dominant accumulation or secondary coarse modes during these months, nor any significant trend in the Ångström Exponent (440–870 nm; r 2 = 0.02). A significant downward seasonal trend in imaginary refractive index (r 2 = 0.43) suggests a trend of decreasing black carbon content in the aerosol composition as the burning season progresses. Similarly, burning season SSA retrievals for the Etosha Pan, Namibia AERONET site also show very similar increasing single scattering albedo values and decreasing imaginary refractive index as the season progresses. Further, retrievals of SSA at 388 nm from the OMI satellite sensor show similar seasonal trends as observed by AERONET and suggest that this seasonal shift is widespread throughout much of southern Africa. A seasonal shift in the satellite retrieval bias of AOD from the MODIS C5 dark target algorithm is consistent with this seasonal SSA trend since the algorithm assumes a constant value of SSA. MISR, however, appears less sensitive to the absorption-induced bias.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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