Assessing the radiative impact of aerosol smoke using MODTRAN™5

Aerosols in the atmosphere affect the Earth's radiation budget in complicated ways, depending on their physical and optical characteristics and how they interact with solar and terrestrial radiation or affect cloud nucleation. While the Arctic atmosphere is generally very clean, spring incursions of haze and dust from Eurasia are known to perturb the surface radiation balance. Recent analyses (based on "Radiative impact of boreal smoke in the Arctic: Observed and modeled", Stone, et al.¹, to be referred to throughout this ms as Stone2008) also reveal that smoke plumes from boreal forest fires can have significant effects during summer. Once aloft, upper-level winds can transport this smoke long distances. In late June and July 2004 fires raged across eastern Alaska and the Yukon and the resulting smoke was advected across the Arctic, reaching as far as Europe. The long-range transport was tracked using a dispersion model² combined with various in situ measurements along its path, all showing enhancements in aerosol opacity. The measurements made at Barrow, Alaska, documented just a portion of the transport and the radiative impact of smoke. The comprehensive measuring systems in place near Barrow (NOAA/GMD³ and DoE/ARM⁴) presented a unique opportunity to characterize the smoke aerosol both physically and optically, and therefore permit quantification of the upwelling radiance (outgoing shortwave radiance - OSR, 0.28 to 4.0 μm) as observed by NASA satellites: Clouds and the Earth's Radiant Energy System (CERES)⁵, coupled with data from Moderate Resolution Imaging Spectroradiometer (MODIS)^6,7,8.