Biomass-burning smoke heights over the Amazon observed from space
Biomass-burning smoke heights over the Amazon observed from space
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DOI：
10.5194/acp-19-1685-2019
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发表时间：
2019-02-08
影响因子：
6.3
通讯作者：
Kahn, Ralph A.
中科院分区：
文献类型：
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作者：
Gonzalez-Alonso, Laura;Martin, Maria Val;Kahn, Ralph A.
我们用MISR和MODIS(2005-2012年)和CALIOP(2006-2012年)观测得到的烟羽的广泛气候学描述了生物质燃烧季节(7-11月)亚马逊地区生物质燃烧排放的垂直分布。烟羽高度表现出很大的变异性，跨度在地形上方几百米至6公里之间。然而，大部分烟雾位于2.5公里以下的高度。约60%的烟羽出现在干旱年份，40%-50%的烟羽出现在燃烧季节的高峰期(9月)，94%的烟羽出现在热带森林和稀树草原地区。在MISR观测时(当地时间10：00-11：00)，最高的羽流出现在草原火灾上空(平均最大羽流高度接近1100米)，最低的羽流出现在热带森林火灾上空(类似800米)。CALIOP在当天晚些时候(14：00-15：00 LT)也发现了类似的模式，尽管在更高的海拔(2300米草原对2000米热带森林)，因为CALIOP通常在更高的海拔探测到烟雾，因为它的飞越时间较晚，与更深的行星边界层，可能更高能量的火焰，以及对薄气溶胶层更敏感。平均而言，3%-20%的火灾向自由对流层注入烟雾；这一比例在燃烧季节结束时(11月：15%-40%)有增加的趋势。我们发现MISR烟羽高度、MODIS火辐射功率和亚马逊主要生态区的大气稳定性之间存在明确的季节循环，在燃烧季节接近尾声时，烟羽更高，火势更大，大气稳定性条件更差。与非干旱(1100米)相比，在干旱期间探测到较低的烟羽高度(800米)，特别是在热带森林和稀树草原火灾上。与热带森林相比，干旱条件更有利于林下火灾，热带森林往往会产生阴燃燃烧和低烟雾喷射高度。干旱似乎也有利于更深的边界层，在这些干燥的条件下，到达自由对流层的烟雾羽流的百分比较低。与以前的研究一致，MISR中可见光气溶胶光学厚度表明，烟雾对亚马逊地区的总气溶胶载量有很大贡献，再加上干旱期间较低的喷射高度，对空气质量有重要影响。这项工作突出了生物群类型、火灾特性以及大气和干旱条件对羽流动力学和烟雾负荷的重要性。此外，我们的研究证明了MISR和CALIOP对亚马逊地区生物质燃烧产生的烟雾垂直分布的联合观测的价值。
We characterise the vertical distribution of biomass-burning emissions across the Amazon during the biomass-burning season (July-November) with an extensive climatology of smoke plumes derived from MISR and MODIS (2005-2012) and CALIOP (2006-2012) observations. Smoke plume heights exhibit substantial variability, spanning a few hundred metres up to 6 km above the terrain. However, the majority of the smoke is located at altitudes below 2.5 km. About 60% of smoke plumes are observed in drought years, 40 %-50 % at the peak month of the burning season (September) and 94% over tropical forest and savanna regions, with respect to the total number of smoke plume observations. At the time of the MISR observations (10:00-11:00 LT), the highest plumes are detected over grassland fires (with an averaged maximum plume height of similar to 1100 m) and the lowest plumes occur over tropical forest fires (similar to 800 m). A similar pattern is found later in the day (14:00-15:00 LT) with CALIOP, although at higher altitudes (2300 m grassland vs. 2000 m tropical forest), as CALIOP typically detects smoke at higher altitudes due to its later overpass time, associated with a deeper planetary boundary layer, possibly more energetic fires, and greater sensitivity to thin aerosol layers. On average, 3 %-20 % of the fires inject smoke into the free troposphere; this percentage tends to increase toward the end of the burning season (November: 15 %-40 %). We find a well-defined seasonal cycle between MISR plume heights, MODIS fire radiative power and atmospheric stability across the main biomes of the Amazon, with higher smoke plumes, more intense fires and reduced atmospheric stability conditions toward the end of the burning season. Lower smoke plume heights are detected during drought 800 m) compared to non-drought (1100 m) conditions, in particular over tropical forest and savanna fires. Drought conditions favour understory fires over tropical forest, which tend to produce smouldering combustion and low smoke injection heights. Droughts also seem to favour deeper boundary layers and the percentage of smoke plumes that reach the free troposphere is lower during these dry conditions. Consistent with previous studies, the MISR mid-visible aerosol optical depth demonstrates that smoke makes a significant contribution to the total aerosol loading over the Amazon, which in combination with lower injection heights in drought periods has important implications for air quality. This work highlights the importance of biome type, fire properties and atmospheric and drought conditions for plume dynamics and smoke loading. In addition, our study demonstrates the value of combining observations of MISR and CALIOP constraints on the vertical distribution of smoke from biomass burning over the Amazon.