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Multi-campaign analysis of smoke properties and cloud interactions in the Southeast Atlantic using ORACLES, LASIC, and CLARIFY data with WRF-CAM5
  • +20
  • Calvin Howes,
  • Pablo Saide,
  • Sharon Burton,
  • Hugh Coe,
  • Amie Dobracki,
  • Marta Fenn,
  • Richard Ferrare,
  • Steffen Freitag,
  • Johnathan Hair,
  • Steven Howell,
  • Siddhant Gupta,
  • Uin Janek,
  • Mary Kacarab,
  • Chongai Kuang,
  • L. Ruby Leung,
  • Athanasios Nenes,
  • Arthur Sedlacek,
  • Kenneth Thornhill,
  • Jenny Wong,
  • Robert Wood,
  • Huihui Wu,
  • Yang Zhang,
  • Paquita Zuidema
Calvin Howes
University of California Los Angeles

Corresponding Author:calvinhowes@ucla.edu

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Pablo Saide
University of California Los Angeles
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Sharon Burton
NASA Langley Research Center
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Hugh Coe
Department of Earth and Environmental Sciences
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Amie Dobracki
University of Hawaii at Manoa
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Marta Fenn
SSAI
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Richard Ferrare
NASA Langley Research Center
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Steffen Freitag
University of Hawaii at Manoa
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Johnathan Hair
NASA Langley Research Center
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Steven Howell
University of Hawaii at Manoa
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Siddhant Gupta
University of Illinois at Urbana Champaign
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Uin Janek
Brookhaven National Laboratory
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Mary Kacarab
University of California Riverside
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Chongai Kuang
Brookhaven National Laboratory
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L. Ruby Leung
Pacific Northwest National Laboratory
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Athanasios Nenes
Ecole Polytechnique Federale de Lausanne
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Arthur Sedlacek
Brookhaven National Lab
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Kenneth Thornhill
NASA Langley Research Center
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Jenny Wong
Mount Allison University
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Robert Wood
University of Washington
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Huihui Wu
University of Manchester
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Yang Zhang
Northeastern University
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Paquita Zuidema
University of Miami
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Abstract

The southeast Atlantic Ocean provides an excellent natural laboratory to study smoke-cloud interactions, a large driver of uncertainty in climate projections. The value of studying this in particular region is largely attributable to two factors---the expansive, bright, semi-permanent stratocumulus cloud deck and the fact that southern Africa is the largest source of biomass-burning aerosols in the world. We study this region using the WRF-Chem model with CAM5 aerosols and in situ observations from the ORACLES, LASIC, and CLARIFY field campaigns, all of which overlapped in August 2017. Across these campaigns, we compare aerosol, cloud, and thermodynamic variables to quantify model performance and expand upon observational findings of aerosol-cloud effects. Specifically, our approach is to analyze aerosol and cloud properties along flight tracks, picking out uniform legs within tropospheric smoke plumes and in the boundary layer. This unique approach allows us to sample the high spatiotemporal variability that can get lost to large-scale averaging. It also allows process-level comparison of local cloud responses to aerosol conditions, and measure model performance in those same processes. Along with better quantifying model predictive power, we find and justify updates to model parameters and processes to better emulate observations, notably aerosol size parameters. Preliminary results suggest that WRF-CAM5 is activating a smaller percentage of aerosols into cloud droplets than shown in observations, which could lead to biased modeling of aerosol indirect radiative effects on a larger scale. We explore this effect further with CCN activation tendency, updraft, particle sizing, and composition analysis, as well as broader dynamics like entrainment and removal rates. Comparing the model with similar instrument suites across multiple colocated campaigns also allows us to quantify instrument uncertainty in ways that a focus on a single campaign cannot and gives further context to the model performance.