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Discussion papers
https://doi.org/10.5194/acp-2019-43
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-43
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 30 Jan 2019

Submitted as: research article | 30 Jan 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Above Cloud Aerosol Optical Depth from airborne observations in the South-East Atlantic

Samuel E. LeBlanc1,2, Jens Redemann3, Connor Flynn4, Kristina Pistone1,2, Meloë Kacenelenbogen1,2, Michal Segal-Rosenheimer1,2, Yohei Shinozuka1,2, Stephen Dunagan2, Robert P. Dahlgren5,2, Kerry Meyer6, James Podolske2, Steven G. Howell7, Steffen Freitag7, Jennifer Small-Griswold7, Brent Holben6, Michael Diamond8, Paola Formenti9, Stuart Piketh10, Gillian Maggs-Kölling11, Monja Gerber11, and Andreas Namwoonde12 Samuel E. LeBlanc et al.
  • 1Bay Area E nvironmental Research Institute, Moffett Field, CA, USA
  • 2NASA Ames Research Center, Moffett Field, CA, USA
  • 3University of Oklahoma, Norman, OK, USA
  • 4Pacific Northwest National Laboratory, Richland, WA, USA
  • 5California State University Monterey Bay, Seaside, CA, USA
  • 6NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 7University of Hawai'i at Mānoa, Honolulu, HI, USA
  • 8University of Washington, Seattle, WA, USA
  • 9LISA, UMR CNRS 7583, Université Paris Est Créteil et Université Paris Diderot, Institut Pierre Simon Laplace, Créteil, France
  • 10NorthWest University, South Africa
  • 11Gobabeb Research and Training Center, Gobabeb, Namibia
  • 12Sam Nujoma Marine and Coastal Resources Research Centre (SANUMARC), University of Namibia, Henties Bay, Namibia

Abstract. The South-East Atlantic (SEA) is host to a climatologically significant biomass burning aerosol layer overlying marine stratocumulus. We present directly measured Above Cloud Aerosol Optical Depth (ACAOD) from the recent ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) airborne field campaign during August and September 2016. In our analysis, we use data from the Spectrometers for Sky-Scanning Sun-Tracking Atmospheric Research (4STAR) instrument and found an average ACAOD of 0.32 at 501 nm, with an average Ångström exponent (AE) of 1.71. The AE is much lower at 1.25 for the full column (including below cloud level aerosol), indicating the presence of large aerosol particles, likely marine aerosol, embedded within the vertical column. ACAOD is observed to be highest near coast at about 12° S, whereas its variability is largest at the southern edge of the average aerosol plume, as indicated by 12 years of MODIS observations. In comparison to MODIS derived ACAOD and long term fine-mode plume-average AOD, the directly-measured ACAOD from 4STAR is slightly lower than the ACAOD product from MODIS. The peak ACAOD expected from long term retrievals is measured to be closer to coast in 2016 at about 1.5°–4° W. By spatially binning the sampled AOD, we obtain a mean ACAOD of 0.37 for the SEA region. Vertical profiles of AOD showcase the variability of the altitude of the aerosol plume and its separation from cloud top. We measured larger AOD at high altitude near coast than farther from coast, while generally observing a larger vertical gap further from coast. Changes of AOD with altitude are correlated with a gas tracer of the biomass burning aerosol plume. Vertical extent of gaps between aerosol and cloud show a large distribution of extent, dominated by near zero gap. The gap distribution with longitude is observed to be largest at about 7° W, farther from coast than expected.

Samuel E. LeBlanc et al.
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Samuel E. LeBlanc et al.
Data sets

Suite of Aerosol, Cloud, and Related Data Acquired Aboard P3 During ORACLES 2016, Version 1 ORACLES Science Team https://doi.org/10.5067/Suborbital/ORACLES/P3/2016_V1

Model code and software

4STAR_codes: 4STAR processing codes 4STAR Team, S. LeBlanc, C. J. Flynn, Y. Shinozuka, M. Segal-Rozenhaimer, K. Pistone, M. Kacenelenbogen, J. Redemann, B. Schmid, P. Russell, J. Livingston, and Q. Zhang https://doi.org/10.5281/zenodo.1492912

samuelleblanc/fp: Moving Lines: NASA airborne research flight planning tool release S. E. LeBlanc https://doi.org/10.5281/zenodo.1478126

Samuel E. LeBlanc et al.
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Short summary
The southeast Atlantic during August–October experiences layers of smoke from biomass burning over marine stratocumulus clouds. Here we present the smoke's light attenuation and its dependence in the spatial, vertical, and spectral domain through direct measurements from an airborne platform during September 2016. From our observations of this climatically important smoke, we found an average of 0.32 aerosol optical depth at 500 nm, slightly lower than comparative satellite measurements.
The southeast Atlantic during August–October experiences layers of smoke from biomass burning...
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