Abstract
Abstract. The vertical distribution of aerosols over Southeast Asia, a critical factor impacting aerosol lifetime, radiative forcing, and precipitation, is examined for the 2006 post El Niño fire burning season. Combining these measurements with remotely sensed land, fire, and meteorological measurements, and fire plume modeling, we have reconfirmed that fire radiative power (FRP) is underestimated over Southeast Asia by MODIS measurements. These results are derived using a significantly different approach from other previously attempted approaches found in the literature. The horizontally constrained Maritime Continent's fire plume median height, using the maximum variance of satellite observed aerosol optical depth as the spatial and temporal constraint, is found to be 2.04 ± 1.52 km during the entirety of the 2006 El Niño fire season, and 2.19±1.50 km for October 2006. This is 0.83 km (0.98 km) higher than random sampling and all other past studies. Additionally, it is determined that 61 (+6–10) % of the bottom of the smoke plume and 83 (+8–11) % of the median of the smoke plume is in the free troposphere during the October maximum; while 49 (+7–9) % and 75 (+12–12) % of the total aerosol plume and the median of the aerosol plume, are correspondingly found in the free troposphere during the entire fire season. This vastly different vertical distribution will have impacts on aerosol lifetime and dispersal. Application of a simple plume rise model using measurements of fire properties underestimates the median plume height by 0.26 km over the entire fire season and 0.34 km over the maximum fire period. It is noted that the model underestimation over the bottom portions of the plume are much larger. The center of the plume can be reproduced when fire radiative power is increased by 20 % (with other parts of the plume ranging from an increase of 0 to 60 % depending on the portion of the plume and the length of the fire season considered). However, to reduce the biases found, improvements including fire properties under cloudy conditions, representation of small-scale convection, and inclusion of aerosol direct and semi-direct effects are required.
Highlights
Quantifying the vertical distribution of aerosols is essential to constrain their atmospheric distribution, which in turn impacts the atmospheric energy budget (Ming et al, 2010; Kim et al, 2008), circulation, clouds and precipitation (Tao et al, 2012; Wang 2013), and human health (Burnett et al, 2014)
The approach allows the vertical distribution of the smoke to be comprehensively sampled, including those obscured by clouds, and aged aerosols which were emitted in the fire and transported significantly downwind
The fire-constrained aggregated daily statistics of the measured vertical aerosol height from CALIPSO (Winker et al, 2003) are given in (Fig. 3a), with the aggregated statistics from the October fire-maximum time and over the fire-constrained region of the bottom, middle-lower, median, middle-upper, and top heights, respectively: 1.68±1.55 km (1.49±1.58 km), 1.92±1.51 km (1.76 ± 1.54 km), 2.19 ± 1.50 km (2.04 ± 1.52 km), 2.53 ± 1.51 km (2.38±1.54 km), and 303±1.52 km (2.91±1.57 km) (Table 1). These results are supported by the statistical values of aerosol heights measured by the micro-pulse lidar station in Singapore throughout the period from 1 September to 30 November 2015 (Fig. S3), which are found to range from 1.6 to 2.4 km. 2015 was selected to compare against groundbased lidar measurements, since it was an El Niño year, and there were no such measurements available from 2006
Summary
Quantifying the vertical distribution of aerosols is essential to constrain their atmospheric distribution, which in turn impacts the atmospheric energy budget (Ming et al, 2010; Kim et al, 2008), circulation, clouds and precipitation (Tao et al, 2012; Wang 2013), and human health (Burnett et al, 2014). There are complicating factors including spatial and temporal heterogeneity in emissions (Cohen and Wang, 2014; Cohen, 2014; Giglio et al, 2006; Petrenko et al, 2012; Wooster et al, 2012), and uncertainties and nonlinearities associated with aerosol processing and removal from the atmosphere (Tao et al, 2012; Cohen and Prinn, 2011; Cohen et al, 2011). Cohen et al.: Vertical distribution of aerosols to longer timescales (Cohen and Wang, 2014; Delene and Ogren, 2002; Dubovik et al, 2000; Cohen et al, 2017)
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