Fire and smoke in the earth system: Evaluating the impact of fire aerosols on regional and global climate.

摘要

Landscape and wildland fires across the globe emit black and organic carbon smoke particles that have atmospheric lifetimes of days to weeks. Some regions, like Africa, experience strong seasonal burning, and other regions, like equatorial Asia, experience substantial interannual variability associated with changes in the El Nino-Southern Oscillation. In equatorial Asia, anthropogenic fires in tropical forests and peatlands produce regionally expansive smoke clouds that have important effects on atmospheric radiation and air quality. I estimated the height of smoke on Borneo and Sumatra and characterized its sensitivity to El Nino and regional drought. My measurements and analyses suggested that direct injection of smoke into the free troposphere within fire plumes was not an important mechanism for vertical mixing of aerosols in equatorial Asia. I also characterized the sensitivity of smoke clouds to regional drought, and investigated how climate responded to the smoke forcing using the Community Atmosphere Model (CAM), version 3. Together, the satellite and modeling results imply a possible positive feedback loop in which anthropogenic burning in the region intensifies drought stress during El Nino. I expanded the scope of this project beyond equatorial Asia and characterized the global climate response to smoke aerosols using the Community Atmosphere Model, version 5 (CAM5), embedded within the Community Earth System Model (CESM). A combination of smoke-induced tropospheric heating and reduced surface temperatures increased equatorial subsidence and weakened and expanded the Hadley cells. As a consequence, precipitation decreased over tropical forests in South America, Africa and equatorial Asia. These results are consistent with the observed correlation between global temperatures and the strength of the Hadley circulation and studies linking black carbon tropospheric heating and tropical expansion.