Abstract. 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
∼1100 m) 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 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.
Dilution impacts on smoke aging: Evidence in BBOP data
