Aerosol profiling with lidar in the Amazon Basin during the wet and dry season

Abstract

[1] For the first time, multiwavelength polarization Raman lidar observations of optical and microphysical particle properties over the Amazon Basin are presented. The fully automated advanced Raman lidar was deployed 60 km north of Manaus, Brazil (2.5 S, 60 W) in the Amazon rain forest from January to November 2008. The measurements thus cover both the wet season (Dec-June) and the dry or burning season (July-Nov). Two cases studies of young and aged smoke plumes are discussed in terms of spectrally resolved optical properties (355, 532, and 1064 nm) and further lidar products such as particle effective radius and single-scattering albedo. These measurement examples confirm that biomass burning aerosols show a broad spectrum of optical, microphysical, and chemical properties. The statistical analysis of the entire measurement period revealed strong differences between the pristine wet and the polluted dry season. African smoke and dust advection frequently interrupt the pristine phases during the wet season. Compared to pristine wet season conditions, the particle scattering coefficients in the lowermost 2 km of the atmosphere were found to be enhanced, on average, by a factor of 4 during periods of African aerosol intrusion and by a factor of 6 during the dry (burning) season. Under pristine conditions, the particle extinction coefficients and optical depth for 532 nm wavelength were frequently as low as 10-30 Mm À1 and <0.05, respectively. During the dry season, biomass burning smoke plumes reached to 3-5 km height and caused a mean optical depth at 532 nm of 0.26. On average during that season, particle extinction coefficients (532 nm) were of the order of 100 Mm À1 in the main pollution layer (up to 2 km height). Ångström exponents were mainly between 1.0 and 1.5, and the majority of the observed lidar ratios were between 50-80 sr.

A permanent Raman lidar station in the Amazon: description, characterization, and first results

“…The period chosen was from 30 August to 6 September 2011 when an intensive campaign for calibration of the water vapor channel of the UV Raman lidar was conducted (to be discussed in an upcoming publication). Particle lidar ratios obtained during nighttime with the use of the Raman channel were between 50 and 65 sr during the whole week, compatible with values found by previous measurements of biomass burning aerosols in the region (Baars et al, 2012). A comparison of the elastic (L p = 55 sr) and Raman aerosol optical depth for each 1 min cloud-free nighttime profile during that week showed no systematic differences, thus allowing us to use the elastic method to compare lidar and AERONET measurements during day time.…”

“…Aerosol plumes with backscatter coefficient larger than 3 Mm −1 sr −1 were also seen on 1 and 2 September and an aerosol layer between 1 and 2.5 km can be identified. This elevated layer appears at heights typical of biomass burning plumes transported over long distances, as characterized by previous lidar studies in the region (Baars et al, 2012). Largest values were around 150 Mm −1 inside the plume.…”

“…(9) and (10) with a particle lidar ratio of 55 sr, which is typical for aged biomass burning aerosols found in this region during the transition from the dry to wet seasons (Baars et al, 2012). This is shown in Fig.…”

“…The long-range transport occurred below 3.5 km, while in clean conditions the biogenic aerosols were found to be trapped below 2 km. Baars et al (2012) showed that column AOD, the maximum extinction and backscatter coefficients during the dry season were about three times higher than during the wet season of 2008. Moreover, an analysis of biomass burning plumes heights indicated that the convective mixing by pyro or deep cumulus was determinant for the vertical distribution of aerosols, indicating the important role of aerosol-cloud interactions in tropical regions (Boucher et al, 2013).…”

HETEAC: The Aerosol Classification Model for EarthCARE

“…In the new OPAC 4.0, three dust components (nucleation, accumulation, and coarse mode) are contained which are made up of nonspherical scatterers of prolate shape. A size-dependent axis-ratio distribution following experimental results [9], at the EARLINET stations of Leipzig and Munich, Germany [10], in the Amazon Basin [11], and onboard Polarstern over the North Atlantic [12]. Simulations were performed using the components of Aerosol_cci (filled stars) and variations with different refractive index and shape distribution (open stars).…”