ALBERT

Description: Microphysical and optical properties of aerosol were studied during mega-fire event in summer 2012 over Siberia using ground-based measurements of spectral solar radiation at AERONET site in Tomsk and satellite observations. The data were analyzed using multiyear (2003–2013) measurements of aerosol characteristics under background conditions and for less intense fires, differing in burning biomass type, stage of fire, remoteness from observation site, etc. ("ordinary fires"). In June–August 2012, the average aerosol optical depth (AOD, 500 nm) had been 0.95 ± 0.86, about a factor of 6 larger than background values (0.16 ± 0.08), and a factor of 2.5 larger than in "ordinary smokes". The AOD values were extremely high on July 24–28 and reached 3–5. Comparison with satellite observations showed that ground-based measurements in the region of Tomsk not only reflect the local AOD features, but also are characteristic for the territory of the Western Siberia as a whole. Single scattering albedo (SSA, 440 nm) in this period ranged from 0.91 to 0.99 with the average of ~ 0.96 in the entire wavelength range of 440–1020 nm. The increase in absorptance of aerosol particles (SSA(440 nm)=0,92) and decrease in SSA with wavelength, observed in "ordinary smokes", agree with the data of multiyear observations in analogous situations in boreal zone of USA and Canada. Volume aerosol size distribution in smoke mist and ordinary smokes had bimodal character with significant prevalence of fine mode particles, but in summer 2012 the mean median radius and the width of the fine mode distribution somewhat increased. In contrast to data of multiyear observations, in summer 2012 an increase in the volume concentration and median radius of the coarse mode was observed with the growing AOD. The calculations of the "average" radiative effects of smoke and background aerosol are presented. As compared to background conditions and "ordinary smokes", under the conditions of smoke mist the cooling effect of aerosol considerably intensifies: direct radiative effects (DRE) at the bottom (BOA) and at the top of the atmosphere (TOA) are −13, −35, and −60 W m−2 and −5, −14, and −35 W m−2 respectively. The maximal values of DRE were observed on July 27 (AOD(500 nm)=3.5), when DRE(BOA) reached −180 W m−2, while DRE(TOA) and DRE of the atmosphere were −80 W m−2.