[1] Single scattering albedo (SSA) governs the strength of aerosols in absorbing solar radiation, but few methods are available to directly measure this important quantity. There currently exist many ground-based measurements of spectral transmittance from which aerosol optical thickness (AOT) are retrieved under clear sky conditions. Reflected radiances at the top of the atmosphere as measured by a spaceborne spectroradiometer are sensitive to both AOT and SSA. On the basis of extensive radiative transfer simulations, it is demonstrated that the combined use of the two measurements allows for the retrieval of SSA at a reasonable accuracy under moderate to heavy aerosol loadings. Retrieval of SSA is most sensitive to AOT and surface reflectance. The accuracy of SSA retrievals increases with aerosol loading.

aerosols, carbon, emissions, FIRE BEAR Project, fire regimes, forest fire behavior, Scotch pine, Siberia,

[1] Heavy loading of aerosols in China is widely known, but little is known about their impact on regional radiation budgets, which is often expressed as aerosol radiative forcing (ARF). Cloud-free direct ARF has either been estimated by models across the region or determined at a handful of locations with aerosol and/or radiation measurements. In this study, ARF is determined at 25 stations distributed across China where aerosol optical thickness has been measured since 2004. In combination with the single-scattering albedo retrieved from ground and satellite measurements, ARF was determined at all the stations at the surface, inside the atmosphere, and at the top of atmosphere (TOA). Nationwide annual and diurnal mean ARF is found to be −15.7 ± 8.9 at the surface, 0.3 ± 1.6 at the TOA, and 16.0 ± 9.2 W m −2 inside the atmosphere. These values imply that aerosols have very little impact on the atmosphere-surface system but substantially warm up the atmosphere at the expense of cooling the surface. The strong atmospheric absorption is likely to alter atmospheric thermodynamic conditions and thus affects circulation considerably.

Fires in boreal and temperate forests play a significant role in the global carbon cycle. While forest fires in North America (NA) have been surveyed extensively by U.S. and Canadian forest services, most fire records are limited to seasonal statistics without information on temporal evolution and spatial expansion. Such dynamic information is crucial for modeling fire emissions. Using the daily Advanced Very High Resolution Radiometer (AVHRR) data archived from 1989 to 2000, an extensive and consistent fire product was developed across the entire NA forest regions on a daily basis at 1-km resolution. The product was generated following data calibration, geo-referencing, and the application of an active fire detection algorithm and a burned area mapping algorithm. The spatial-temporal variation of forest fire in NA is analyzed in terms of (1) annual and monthly patterns of fire occurrences in different eco-domains, (2) the influence of topographic factors (elevation zones, aspect classes, and slope classes), and (3) major forest types and eco-regions in NA. It was found that 1) among the 12 years analyzed, 1989 and 1995 were the most severe fire years in NA; 2) the majority of burning occurred during June-July and in low elevation zones (b 500 m) with gentle slopes (b 10°), except in the dry eco-domain where more fires occurred in higher elevation zones (N 2000 m); 3) most fires occurred in the polar ecodomain, sub-arctic eco-division, and in the taiga (boreal forests), forest-tundras and open woodlands eco-provinces in the boreal forests of Canada. The tendency for multiple burns to occur increases with elevation and slope until about 2500 m elevation and 24°slope, and decreases therefore. In comparison with ground observations, the omission and commission errors are on the order of 20%.