The Direct Radiative Forcing of Biomass Burning Aerosols: Investigations during SCAR-B and ZIBBEE

Biomass burning aerosols have a wide spatial distribution that is governed by the geographic distribution of their source regions and tropospheric circulation. Annually, more than 114 Tg of smoke is produced that have residence times ranging from days to weeks depending upon their size and chemical composition. These aerosols reflect the incoming solar directly which is called the “direct effect ” and they also modify the reflective properties of clouds which is called the “indirect effect”. The direct top of atmosphere (TOA) globally averaged radiative forcing estimates range from-0.2 to-1.1 W/m2. The uncertainties in this estimate are due to the various assumptions (see Introduction) involved in the calculations. While the TOA radiative forcing estimates provide valuable information on the effects of aerosols on climate, equally important are the downward shortwave irradiances (DSWI) at the surface and the atmospheric heating/cooling rate profiles. For example, the DSWI irradiance calculations show large discrepancies between measurements and calculations in the presence of biomas