Journal article
On the differences in the vertical distribution of modeled aerosol opticaldepth over the southeastern Atlantic
Atmospheric chemistry and physics, Vol.23(7), pp.4283-4309
04/12/2023
DOI: 10.5194/acp-23-4283-2023
Abstract
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 degrees S- 0 degrees N-S and 15 degrees W-15 degrees 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.
Details
- Title: Subtitle
- On the differences in the vertical distribution of modeled aerosol opticaldepth over the southeastern Atlantic
- Creators
- Ian Chang - University of OklahomaLan Gao - University of OklahomaConnor J. Flynn - University of OklahomaYohei Shinozuka - Ames Research CenterSarah J. Doherty - University of WashingtonMichael S. Diamond - Florida State Univ, Dept Earth Ocean & Atmospher Sci, Tallahassee, FL USAKarla M. Longo - Instituto Nacional de Pesquisas EspaciaisGonzalo A. Ferrada - Univ Iowa, Ctr Global & Reg Environm Res, Iowa City, IA USAGregory R. Carmichael - University of IowaPatricia Castellanos - NASA, Climate & Radiat Lab, Goddard Space Flight Ctr, Greenbelt, MD USAArlindo M. da Silva - NASA, Climate & Radiat Lab, Goddard Space Flight Ctr, Greenbelt, MD USAPablo E. Saide - Univ Calif Los Angeles, Inst Environm & Sustainabil, Los Angeles, CA USACalvin Howes - Univ Calif Los Angeles, Dept Atmospher & Ocean Sci, Los Angeles, CA USAZhixin Xue - University of AlabamaMarc Mallet - Météo-FranceRavi Govindaraju - Sci Syst & Applicat Inc, Greenbelt, MD USAQiaoqiao Wang - Jinan Univ, Inst Environm & Climate Res, Guangzhou 510632, Peoples R ChinaYafang Cheng - Max Planck Institute for ChemistryYan Feng - Argonne Natl Lab, Div Environm Sci, Argonne, IL USASharon P. Burton - NASA, Langley Res Ctr, Hampton, VA USARichard A. Ferrare - NASA, Langley Res Ctr, Hampton, VA USASamuel E. LeBlanc - Ames Research CenterMeloe S. Kacenelenbogen - NASA, Climate & Radiat Lab, Goddard Space Flight Ctr, Greenbelt, MD USAKristina Pistone - Ames Research CenterMichal Segal-Rozenhaimer - Ames Research CenterKerry G. Meyer - NASA, Climate & Radiat Lab, Goddard Space Flight Ctr, Greenbelt, MD USAJu-Mee Ryoo - Ames Research CenterLeonhard Pfister - Ames Research CenterAdeyemi A. Adebiyi - Univ Calif Merced, Dept Life & Environm Sci, Merced, CA USARobert Wood - University of WashingtonPaquita Zuidema - University of MiamiSundar A. Christopher - University of AlabamaJens Redemann - University of Oklahoma
- Resource Type
- Journal article
- Publication Details
- Atmospheric chemistry and physics, Vol.23(7), pp.4283-4309
- DOI
- 10.5194/acp-23-4283-2023
- ISSN
- 1680-7316
- eISSN
- 1680-7324
- Publisher
- Copernicus Gesellschaft Mbh
- Number of pages
- 27
- Grant note
- 122007900 / University of Oklahoma NNH13ZDA001N-EVS2 / NASA Earth Venture Suborbital-2program DE-AC02-06CH11357 / U.S. DOE Office of Science; United States Department of Energy (DOE) OE Office of Biological and Environmental Research
- Language
- English
- Date published
- 04/12/2023
- Academic Unit
- Civil and Environmental Engineering; Iowa Technology Institute; Center for Global & Regional Environmental Research; Nursing; Chemical and Biochemical Engineering
- Record Identifier
- 9984442025602771
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