On the differences in the vertical distribution of modeled aerosol optical depth over the southeastern Atlantic

I. Chang; L. Gao; C. J. Flynn; Y. Shinozuka; Y. Shinozuka; S. J. Doherty; S. J. Doherty; M. S. Diamond; K. M. Longo; G. A. Ferrada; G. A. Ferrada; G. R. Carmichael; P. Castellanos; A. M. da Silva; P. E. Saide; P. E. Saide; C. Howes; Z. Xue; Z. Xue; M. Mallet; R. Govindaraju; Q. Wang; Y. Cheng; Y. Feng; S. P. Burton; R. A. Ferrare; S. E. LeBlanc; S. E. LeBlanc; M. S. Kacenelenbogen; K. Pistone; K. Pistone; M. Segal-Rozenhaimer; M. Segal-Rozenhaimer; M. Segal-Rozenhaimer; K. G. Meyer; J.-M. Ryoo; J.-M. Ryoo; L. Pfister; A. A. Adebiyi; R. Wood; P. Zuidema; S. A. Christopher; J. Redemann

doi:10.5194/acp-23-4283-2023

Atmospheric Chemistry and Physics (Apr 2023)

On the differences in the vertical distribution of modeled aerosol optical depth over the southeastern Atlantic

I. Chang,
L. Gao,
C. J. Flynn,
Y. Shinozuka,
Y. Shinozuka,
S. J. Doherty,
S. J. Doherty,
M. S. Diamond,
K. M. Longo,
G. A. Ferrada,
G. A. Ferrada,
G. R. Carmichael,
P. Castellanos,
A. M. da Silva,
P. E. Saide,
P. E. Saide,
C. Howes,
Z. Xue,
Z. Xue,
M. Mallet,
R. Govindaraju,
Q. Wang,
Y. Cheng,
Y. Feng,
S. P. Burton,
R. A. Ferrare,
S. E. LeBlanc,
S. E. LeBlanc,
M. S. Kacenelenbogen,
K. Pistone,
K. Pistone,
M. Segal-Rozenhaimer,
M. Segal-Rozenhaimer,
M. Segal-Rozenhaimer,
K. G. Meyer,
J.-M. Ryoo,
J.-M. Ryoo,
L. Pfister,
A. A. Adebiyi,
R. Wood,
P. Zuidema,
S. A. Christopher,
J. Redemann

Affiliations

I. Chang: School of Meteorology, University of Oklahoma, Norman, Oklahoma, USA
L. Gao: School of Meteorology, University of Oklahoma, Norman, Oklahoma, USA
C. J. Flynn: School of Meteorology, University of Oklahoma, Norman, Oklahoma, USA
Y. Shinozuka: NASA Ames Research Center, Moffett Field, California, USA
Y. Shinozuka: Bay Area Environmental Research Institute, Moffett Field, California, USA
S. J. Doherty: Cooperative Institute for Climate, Ocean and Ecosystem Studies, University of Washington, Seattle, Washington, USA
S. J. Doherty: Department of Atmospheric Science, University of Washington, Seattle, Washington, USA
M. S. Diamond: Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, Florida, USA
K. M. Longo: National Institute for Space Research, São José dos Campos, Brazil
G. A. Ferrada: Center for Global and Regional Environmental Research, University of Iowa, Iowa City, Iowa, USA
G. A. Ferrada: Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, Tennessee, USA
G. R. Carmichael: Center for Global and Regional Environmental Research, University of Iowa, Iowa City, Iowa, USA
P. Castellanos: Climate and Radiation Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
A. M. da Silva: Climate and Radiation Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
P. E. Saide: Institute of the Environment and Sustainability, University of California, Los Angeles, Los Angeles, California, USA
P. E. Saide: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California, USA
C. Howes: Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California, USA
Z. Xue: Department of Atmospheric and Earth Science, University of Alabama in Huntsville, Huntsville, Alabama, USA
Z. Xue: Center for Global and Regional Environmental Research, University of Iowa, Iowa City, Iowa, USA
M. Mallet: Centre National de Recherches Météorologiques, UMR3589, Météo-France-CNRS, Toulouse, France
R. Govindaraju: Science Systems and Applications, Inc., Greenbelt, Maryland, USA
Q. Wang: Institute for Environmental and Climate Research, Jinan University, 510632 Guangzhou, China
Y. Cheng: Minerva Research Group, Max Planck Institute for Chemistry, 55128 Mainz, Germany
Y. Feng: Environmental Science Division, Argonne National Laboratory, Argonne, Illinois, USA
S. P. Burton: NASA Langley Research Center, Hampton, Virginia, USA
R. A. Ferrare: NASA Langley Research Center, Hampton, Virginia, USA
S. E. LeBlanc: NASA Ames Research Center, Moffett Field, California, USA
S. E. LeBlanc: Bay Area Environmental Research Institute, Moffett Field, California, USA
M. S. Kacenelenbogen: Climate and Radiation Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
K. Pistone: NASA Ames Research Center, Moffett Field, California, USA
K. Pistone: Bay Area Environmental Research Institute, Moffett Field, California, USA
M. Segal-Rozenhaimer: NASA Ames Research Center, Moffett Field, California, USA
M. Segal-Rozenhaimer: Bay Area Environmental Research Institute, Moffett Field, California, USA
M. Segal-Rozenhaimer: Department of Geophysics, Porter School of the Environment and Earth Sciences, Tel-Aviv University, Tel-Aviv, Israel
K. G. Meyer: Climate and Radiation Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
J.-M. Ryoo: NASA Ames Research Center, Moffett Field, California, USA
J.-M. Ryoo: Science and Technology Corporation (STC), Moffett Field, California, USA
L. Pfister: NASA Ames Research Center, Moffett Field, California, USA
A. A. Adebiyi: Department of Life and Environmental Sciences, University of California, Merced, Merced, California, USA
R. Wood: Department of Atmospheric Science, University of Washington, Seattle, Washington, USA
P. Zuidema: Rosenstiel School of Marine, Atmospheric, and Earth Science, University of Miami, Miami, Florida, USA
S. A. Christopher: Department of Atmospheric and Earth Science, University of Alabama in Huntsville, Huntsville, Alabama, USA
J. Redemann: School of Meteorology, University of Oklahoma, Norman, Oklahoma, USA

DOI: https://doi.org/10.5194/acp-23-4283-2023
Journal volume & issue: Vol. 23
pp. 4283 – 4309

Abstract

Read online

The southeastern Atlantic is home to an expansive smoke aerosol plume overlying a large cloud deck for approximately a third of the year. The aerosol plume is mainly attributed to the extensive biomass burning activities that occur in southern Africa. Current Earth system models (ESMs) reveal significant differences in their estimates of regional aerosol radiative effects over this region. Such large differences partially stem from uncertainties in the vertical distribution of aerosols in the troposphere. These uncertainties translate into different aerosol optical depths (AODs) in the planetary boundary layer (PBL) and the free troposphere (FT). This study examines differences of AOD fraction in the FT and AOD differences among ESMs (WRF-CAM5, WRF-FINN, GEOS-Chem, EAM-E3SM, ALADIN, GEOS-FP, and MERRA-2) and aircraft-based measurements from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign. Models frequently define the PBL as the well-mixed surface-based layer, but this definition misses the upper parts of decoupled PBLs, in which most low-level clouds occur. To account for the presence of decoupled boundary layers in the models, the height of maximum vertical gradient of specific humidity profiles from each model is used to define PBL heights. Results indicate that the monthly mean contribution of AOD in the FT to the total-column AOD ranges from 44 % to 74 % in September 2016 and from 54 % to 71 % in August 2017 within the region bounded by 25∘ S–0∘ N–S and 15∘ W–15∘ E (excluding land) among the ESMs. ALADIN and GEOS-Chem show similar aerosol plume patterns to a derived above-cloud aerosol product from the Moderate Resolution Imaging Spectroradiometer (MODIS) during September 2016, but none of the models show a similar above-cloud plume pattern to MODIS in August 2017. Using the second-generation High Spectral Resolution Lidar (HSRL-2) to derive an aircraft-based constraint on the AOD and the fractional AOD, we found that WRF-CAM5 produces 40 % less AOD than those from the HSRL-2 measurements, but it performs well at separating AOD fraction between the FT and the PBL. AOD fractions in the FT for GEOS-Chem and EAM-E3SM are, respectively, 10 % and 15 % lower than the AOD fractions from the HSRL-2. Their similar mean AODs reflect a cancellation of high and low AOD biases. Compared with aircraft-based observations, GEOS-FP, MERRA-2, and ALADIN produce 24 %–36 % less AOD and tend to misplace more aerosols in the PBL. The models generally underestimate AODs for measured AODs that are above 0.8, indicating their limitations at reproducing high AODs. The differences in the absolute AOD, FT AOD, and the vertical apportioning of AOD in different models highlight the need to continue improving the accuracy of modeled AOD distributions. These differences affect the sign and magnitude of the net aerosol radiative forcing, especially when aerosols are in contact with clouds.

Published in Atmospheric Chemistry and Physics

ISSN: 1680-7316 (Print); 1680-7324 (Online)
Publisher: Copernicus Publications
Country of publisher: Germany
LCC subjects: Science: Physics; Science: Chemistry
Website: http://www.atmospheric-chemistry-and-physics.net/

About the journal