Do biomass burning aerosols intensify drought in equatorial Asia during El Nino?
Do biomass burning aerosols intensify drought in equatorial Asia during El Nino?
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DOI：
10.5194/acp-10-3515-2010
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发表时间：
2010-01-01
影响因子：
6.3
通讯作者：
Rasch, P. J.
中科院分区：
文献类型：
--
作者：
Tosca, M. G.;Randerson, J. T.;Rasch, P. J.
在厄尔尼诺年间，赤道亚洲热带森林和泥炭地的大火造成了大片区域烟云。我们描述了这些云对区域干旱的敏感性，并利用大气环流模式研究了它们对气候的影响。2000-2006年期间的卫星观测表明，厄尔尼诺引起的区域干旱导致火灾排放增加，从而增加了苏门答腊岛、婆罗洲和周围海洋的气溶胶光学厚度。接下来，我们使用社区大气模式(CAM)来研究气候如何响应这种强迫。我们进行了两次30年的模拟，使用卫星获取的火灾排放时间序列，为高火年(El Nino，1997)或低火年(La Nina，2000)规定了每月的火灾排放量。我们的模拟包括了气溶胶对模式内辐射收支的直接和半直接影响。我们通过分析高火和低火模拟的差异，评估了人为火灾的辐射和气候效应。8-10月期间，在苏门答腊岛和婆罗洲大部分地区(东经90度-东经120度，北纬5度S-5度)，火气溶胶使地表的净短波辐射减少了19.1+/-12.9W m(-2)(10%)。在这几个月中，净短波辐射的减少使海表面温度和陆地表面温度分别降低了0.5+/-0.3和0.4+/-0.2摄氏度。来自黑碳(BC)吸收的对流层加热平均为20.5+/-9.3Wm(-2)，并通过减少潜热来平衡。海温的降低和大气加热的增加使区域降水量减少了0.9+/-0.6 mm d(-1)(10%)。由于降雨量的减少超过了蒸散的减少，生态系统对火灾的脆弱性增加了。总而言之，卫星和模拟结果暗示了一个可能的正反馈循环，在这个循环中，该地区的人为燃烧加剧了厄尔尼诺期间的干旱压力。
During El Nino years, fires in tropical forests and peatlands in equatorial Asia create large regional smoke clouds. We characterized the sensitivity of these clouds to regional drought, and we investigated their effects on climate by using an atmospheric general circulation model. Satellite observations during 2000-2006 indicated that El Nino-induced regional drought led to increases in fire emissions and, consequently, increases in aerosol optical depths over Sumatra, Borneo and the surrounding ocean. Next, we used the Community Atmosphere Model (CAM) to investigate how climate responded to this forcing. We conducted two 30 year simulations in which monthly fire emissions were prescribed for either a high (El Nino, 1997) or low (La Nina, 2000) fire year using a satellite-derived time series of fire emissions. Our simulations included the direct and semi-direct effects of aerosols on the radiation budget within the model. We assessed the radiative and climate effects of anthropogenic fire by analyzing the differences between the high and low fire simulations. Fire aerosols reduced net shortwave radiation at the surface during August-October by 19.1 +/- 12.9 W m(-2) (10%) in a region that encompassed most of Sumatra and Borneo (90 degrees E-120 degrees E, 5 degrees S-5 degrees N). The reductions in net shortwave radiation cooled sea surface temperatures (SSTs) and land surface temperatures by 0.5 +/- 0.3 and 0.4 +/- 0.2 degrees C during these months. Tropospheric heating from black carbon (BC) absorption averaged 20.5 +/- 9.3 W m(-2) and was balanced by a reduction in latent heating. The combination of decreased SSTs and increased atmospheric heating reduced regional precipitation by 0.9 +/- 0.6 mm d(-1) (10%). The vulnerability of ecosystems to fire was enhanced because the decreases in precipitation exceeded those for evapotranspiration. 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.