Biomass burning smoke heights over the Amazon observed from space

Abstract. We characterize the vertical distribution of biomass burning emissions across the Amazon during the biomass burning season 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 meters 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 during drought years, at the peak month of the burning season (September; 40–50 %) and over tropical forest and savanna regions (94 %). At the time of the MISR observations (10:00–11:00 LT), the highest plumes are detected over grassland fires (1100 m maximum plume height average) and the lowest plumes occur over tropical forest fires (~ 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 versus 2000 m tropical forest), as CALIOP typically detects smoke at higher altitudes due to its greater sensitivity to thin aerosol layers. On average, 3–20 % of the fires inject smoke into the free troposphere; this percentage can 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 (FRP) 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 FT 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, with important implications for air quality. This work highlights the importance of biome type, fire properties and atmospheric conditions for plume dynamics, as well as the effect of drought conditions on smoke loading. In addition, our study demonstrates that combined observations of MISR and CALIOP allows for better constraints on the vertical distribution of smoke from biomass burning over the Amazon.