Biomass Burning Induced Surface Darkening and Its Impact on Regional Meteorology in Eastern China

With the tendency of global warming and land use cover change, global threats from Biomass Burning (BB) are increasing dramatically and has attracted widespread attention. Most pre-existing studies in the past focused on impacts of BB emissions on air quality and climate, but in fact, BB will also bring great changes to land surface, which would affect the thermal motion of atmosphere in turn. Large areas of dark char, a carbon residue from partially combusted vegetation, will stick to the ground surface in burned area after open biomass combustion processes. BB has significant seasonal variations and distinct regional characteristics. Intense wheat straw burning events occur in eastern plain of China every June. Based on MODIS satellite retrievals, wheat straw burning in eastern China in June could induce surface albedo relatively decrease up to about 35%~85% in burned area, which could be called “darkening effect”. The absolute decrease in surface albedo mainly range in -0.02 ~ -0.16 in near-infrared broadband. By combining with WRF-Chem simulation, obvious signals of positive radiative effect showed in the eastern plain of China with the same pattern as ‘darkening area’. Besides, unbalanced surface warming induced by darkening effect of biomass burning could make changes in regional near surface thermodynamic circulation directly. After considering the decrease in surface albedo caused by BB, temperature anomalies can be simulated to some extent. Furthermore, it can be found that a phenomenon of surface warming will show in the downwind area of severe burned area in eastern china on clear-sky days after biomass burning, based on temperature observations of multi-years. The temperature profile in PBL shows in obvious warming in lower levels at 20:00 LT while almost unchanged at 8:00, which could be explained as the re-balance of surface radiation after albedo change. Since surface warming in ’burned scar’ induced by albedo decrease requires a process of radiative accumulation and then affect the entire region circulation field through thermal disturbance, a certain response time generates. This can explain why the impact on temperature simulation tends to be more obvious in the afternoon of evening.