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Title: Modeling the smoky troposphere of the southeast Atlantic: a comparison to ORACLES airborne observations from September of 2016

Journal Article · · Atmospheric Chemistry and Physics (Online)
 [1]; ORCiD logo [2]; ORCiD logo [3];  [4];  [4];  [5]; ORCiD logo [6];  [7];  [8]; ORCiD logo [9];  [10]; ORCiD logo [11];  [12]; ORCiD logo [13];  [13]; ORCiD logo [14];  [15];  [14]; ORCiD logo [14];  [16] more »;  [15];  [15];  [3];  [17];  [18];  [15];  [19];  [16];  [14]; ORCiD logo [20]; ORCiD logo [21]; ORCiD logo [12] « less
  1. Universities Space Research Association, Columbia, MD (United States); NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States)
  2. Univ. of California, Los Angeles, CA (United States)
  3. Univ. of Iowa, Iowa City, IA (United States)
  4. NASA Langley Research Center, Hampton, VA (United States)
  5. Joint Institute for the Study of the Atmosphere and Ocean, Seattle, WA (United States); Univ. of Washington, Seattle, WA (United States)
  6. University of Leeds (United Kingdom)
  7. Universities Space Research Association, Columbia, MD (United States); NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  8. CNRM, Toulouse (France)
  9. Argonne National Lab. (ANL), Argonne, IL (United States)
  10. Jinan Univ., Guangzhou, Guangdong (China)
  11. Max Planck Institute for Chemistry, Mainz (Germany)
  12. Univ. of Miami, FL (United States)
  13. Univ. of Hawaii at Manoa, Honolulu, HI (United States)
  14. NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States); Bay Area Environmental Research Institute, Moffett Field, CA (United States)
  15. Bay Area Environmental Research Institute, Moffett Field, CA (United States)
  16. NASA Ames Research Center (ARC), Moffett Field, Mountain View, CA (United States)
  17. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  18. Science Systems and Applications, Inc, Greenbelt, MD (United States)
  19. Northeastern Univ., Boston, MA (United States)
  20. Univ. of Oklahoma, Norman, OK (United States)
  21. Univ. of Washington, Seattle, WA (United States)
+ Show Author Affiliations

In the southeast Atlantic, well-defined smoke plumes from Africa advect over marine boundary layer cloud decks; both are most extensive around September, when most of the smoke resides in the free troposphere. A framework is put forth for evaluating the performance of a range of global and regional atmospheric composition models against observations made during the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) airborne mission in September 2016. A strength of the comparison is a focus on the spatial distribution of a wider range of aerosol composition and optical properties than has been done previously. The sparse airborne observations are aggregated into approximately 2° grid boxes and into three vertical layers: 3–6 km, the layer from cloud top to 3 km, and the cloud-topped marine boundary layer. Simulated aerosol extensive properties suggest that the flight-day observations are reasonably representative of the regional monthly average, with systematic deviations of 30 % or less. Evaluation against observations indicates that all models have strengths and weaknesses, and there is no single model that is superior to all the others in all metrics evaluated. Whereas all six models typically place the top of the smoke layer within 0–500 m of the airborne lidar observations, the models tend to place the smoke layer bottom 300–1400 m lower than the observations. A spatial pattern emerges, in which most models underestimate the mean of most smoke quantities (black carbon, extinction, carbon monoxide) on the diagonal corridor between 16° S, 6° E, and 10° S, 0° E, in the 3–6 km layer, and overestimate them further south, closer to the coast, where less aerosol is present. Model representations of the above-cloud aerosol optical depth differ more widely. Most models overestimate the organic aerosol mass concentrations relative to those of black carbon, and with less skill, indicating model uncertainties in secondary organic aerosol processes. Regional-mean free-tropospheric model ambient single scattering albedos vary widely, between 0.83 and 0.93 compared with in situ dry measurements centered at 0.86, despite minimal impact of humidification on particulate scattering. The modeled ratios of the particulate extinction to the sum of the black carbon and organic aerosol mass concentrations (a mass extinction efficiency proxy) are typically too low and vary too little spatially, with significant inter-model differences. Most models overestimate the carbonaceous mass within the offshore boundary layer. Overall, the diversity in the model biases suggests that different model processes are responsible. The wide range of model optical properties requires further scrutiny because of their importance for radiative effect estimates.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Atmospheric Radiation Measurement (ARM) Data Center; Argonne National Laboratory (ANL), Argonne, IL (United States); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER); National Aeronautics and Space Administration (NASA); North American Electric Reliability Corporation (NERC); USEPA
Grant/Contract Number:
SC0018272; AC02-05CH11231; AC02-06CH11357; SC0006695; NNH13ZDA001N-EVS2; NE/L013479/1; RD835871; ACI-1053575
OSTI ID:
1842519
Alternate ID(s):
OSTI ID: 1681043; OSTI ID: 1833627
Journal Information:
Atmospheric Chemistry and Physics (Online), Vol. 20, Issue 19; ISSN 1680-7324
Publisher:
Copernicus Publications, EGUCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (5)

The diurnal cycle of the smoky marine boundary layer observed during August in the remote southeast Atlantic journal January 2019
Above-cloud aerosol optical depth from airborne observations in the southeast Atlantic journal January 2020
Development of aerosol activation in the double-moment Unified Model and evaluation with CLARIFY measurements journal January 2020
Vertical variability of the properties of highly aged biomass burning aerosol transported over the southeast Atlantic during CLARIFY-2017 journal January 2020
Direct and semi-direct radiative forcing of biomass-burning aerosols over the southeast Atlantic (SEA) and its sensitivity to absorbing properties: a regional climate modeling study journal January 2020

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