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1 During the dry season, anthropogenic fires in tropical forests and peatlands of equatorial Asia produce regionally expansive smoke clouds that have important effects on atmospheric radiation and air quality. Here we estimated the height of smoke on Borneo and Sumatra and characterized its sensitivity to El Niño and regional drought. We used Multiangle Imaging Spectroradiometer (MISR) satellite data and the MISR Interactive Explorer (MINX) software to estimate the heights of 317 smoke plumes on Borneo and 139 plumes on Sumatra during 2001–2009. In addition, we estimated the altitudes of larger smoke regions (smoke clouds) over Borneo using data from MISR and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) products. Most smoke plumes on Borneo (83%) were observed during El Niño years. Annually averaged plume heights on Borneo were significantly higher during El Niño events. Mean MISR-derived plume heights were 709 ± 14 m on Borneo and 749 ± 24 m on Sumatra during 2001–2009, with 96% of all plumes confined to within 500 m of the atmospheric boundary layer. Smoke clouds on Borneo were observed at altitudes between 1000 and 2000 m as measured by both MISR and CALIPSO. The difference in height between individual plumes and longer-lived regional smoke clouds may be related to deeper planetary boundary layers and higher-intensity fires later in the afternoon or other atmospheric mixing processes that occur on synoptic time scales. Our 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.
Tosca et al. (Thu,) studied this question.