Effects of Siberian forest fires on regional climate in spring 2003

Forest fires are one of important sources for carbonaceous aerosols which are mostly comprised of organic carbon (OC) and black carbon (BC) aerosols. They have important climatic implications because of their extinction of solar radiation: OC scatters and BC absorbs solar radiation. These contrasting radiative properties add another complexity to our understanding the effects of those aerosols on climate. In spring 2003, the record-breaking intense forest fires occurred over Siberia, which emitted huge amount of aerosols in the atmosphere. We here examine the effect of these Siberian forest fires aerosols on regional climate in East Asia using a combination of numerical models and observations. First a global chemical transport model (CTM) with a biomass burning emission inventory constrained by satellite was used to simulate the enhancements of the aerosol concentrations due to the Siberian fires over East Asia. Our simulated aerosols were evaluated against the observations from the MODIS satellite and at the EANET sites. We then applied the simulated aerosols concentrations to climate simulations using the National Center for Atmospheric Research (NCAR) coupled global climate model, Community Climate System Model version 3.0 (CCSM3) to examine the impact of Siberian fire aerosols on regional climate. The difference in the model between with and without simulated Siberian fire aerosols defines the impact of fires on regional climate. The results indicated that fire aerosols resulted in a strong cooling at the surface and a general warming in the free troposphere and thus increased atmospheric stability. We also found significant decreases in geopotential heights over Siberia and decreases in cloud cover and precipitation in both Japan and the western North Pacific due to fire aerosols. Such changes were consistent with the observations based on the NCEP/DOE reanalysis II data, indicating the importance of fire impacts for regional climate simulations.