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Total spectral solar irradiance and biologically active solar ultraviolet radiation (UVery, 280–315 nm) have been monitored during biomass burning period of moist deciduous forests in the Northeastern India. Aerosol optical depth values varied from 0.5 to 4.2 during different stages of burning. Total solar irradiance measurements suggested decrease in direct solar irradiance during burning with increase in diffused radiation. A statistical fit of AOD (500 nm) through UVery shows negative gradient and for every 0.1 increase in aerosol optical depth during biomass burning period 0.01 W m-2 reduction in the ground reaching UVery has been observed. [Copyright &y& Elsevier]

Physical and optical properties of biomass burning aerosols in Northeastern region, India analyzed based on measurements made during February 2002. Large spatial extent of Northeastern Region moist tropical to moist sub-tropical forests in India have high frequency of burning in annual dry seasons. Characterization of resultant trace gases and aerosols from biomass burning is important for the atmospheric radiative processes. Aerosol optical depth (AOD) observed to be high during burning period compared to pre- and post-burning days. Peak period of biomass burning is highly correlated with measured AOD and total columnar water vapor. Size distribution of aerosols showed bimodal size distribution during burning day and unimodal size distribution during pre- and post-burning days. Size distribution retrievals from biomass burning aerosols show dominance of accumulation mode particles. Weighted mean radius is high (0.22 μm) during burning period. Columnar content of aerosols observed to be high during burning period in addition to the drastic reduction of visibility. During the burning day Anderson sampler measurements showed dominance of accumulation mode particles. The diurnal averaged values of surface shortwave aerosol radiative forcing of biomass burning aerosols varies from −59 to −87 W m−2 on different days. Measured and modeled solar irradiances are also discussed in the paper. [Copyright &y& Elsevier]