Preprints
https://doi.org/10.5194/acp-2021-677
https://doi.org/10.5194/acp-2021-677

  09 Sep 2021

09 Sep 2021

Review status: this preprint is currently under review for the journal ACP.

Precipitation Susceptibility of Marine Stratocumulus with Variable Above and Below-Cloud Aerosol Concentrations over the Southeast Atlantic

Siddhant Gupta1,2, Greg M. McFarquhar1,2, Joseph R. O'Brien3, Michael R. Poellot3, David J. Delene3, Rose M. Miller4, and Jennifer D. Small Griswold5 Siddhant Gupta et al.
  • 1Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Norman, OK, USA
  • 2School of Meteorology, University of Oklahoma, Norman, OK, USA
  • 3Department of Atmospheric Sciences, University of North Dakota, Grand Forks, ND, USA
  • 4Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, IL, USA
  • 5Department of Meteorology, University of Hawai’i at Manoa, Honolulu, HI, USA

Abstract. Aerosol-cloud-precipitation interactions (ACIs) provide the greatest source of uncertainties in predicting changes in Earth’s energy budget due to poor representation of marine stratocumulus and the associated ACIs in climate models. Using in situ data from 329 cloud profiles across 24 research flights from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign in September 2016, August 2017, and October 2018, it is shown that contact between above-cloud biomass-burning aerosols and marine stratocumulus over the southeast Atlantic Ocean was associated with precipitation suppression and a decrease in the precipitation susceptibility (So) to aerosols. The 173 “contact” profiles with aerosol concentration (Na) greater than 500 cm−3 within 100 m above cloud tops had 50 % lower precipitation rate (Rp) and 20 % lower So, on average, compared to 156 “separated” profiles with Na less than 500 cm−3 up to at least 100 m above cloud tops.

Contact and separated profiles had statistically significant differences in droplet concentration (Nc) and effective radius (Re) (95 % confidence intervals from a two-sample t-test are reported). Contact profiles had 84 to 90 cm−3 higher Nc and 1.4 to 1.6 μm lower Re compared to separated profiles. In clean boundary layers (below-cloud Na less than 350 cm−3), contact profiles had 25 to 31 cm−3 higher Nc and 0.2 to 0.5 μm lower Re. In polluted boundary layers (below-cloud Na exceeding 350 cm−3), contact profiles had 98 to 108 cm−3 higher Nc and 1.6 to 1.8 μm lower Re. On the other hand, contact and separated profiles had statistically insignificant differences between the average liquid water path, cloud thickness, and meteorological parameters like surface temperature, lower tropospheric stability, and estimated inversion strength. These results suggest the changes in cloud properties were driven by ACIs rather than meteorological effects, and the existing relationships between Rp and Nc must be adjusted to account for the role of ACIs.

Siddhant Gupta et al.

Status: open (until 21 Oct 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Siddhant Gupta et al.

Data sets

Suite of Aerosol, Cloud, and Related Data Acquired Aboard P3 During ORACLES 2018, Version 2 ORACLES Science Team https://doi.org/10.5067/Suborbital/ORACLES/P3/2018_V2

Suite of Aerosol, Cloud, and Related Data Acquired Aboard P3 During ORACLES 2017, Version 2 ORACLES Science Team https://doi.org/10.5067/Suborbital/ORACLES/P3/2017_V2

Suite of Aerosol, Cloud, and Related Data Acquired Aboard P3 During ORACLES 2016, Version 2 ORACLES Science Team https://doi.org/10.5067/Suborbital/ORACLES/P3/2016_V2

Model code and software

Airborne Data Processing and Analysis Software Package (Version 3981) David J. Delene A. Skow, J. O'Brien, N. Gapp, S. Wagner, K. Hibert, K. Sand, and G. Sova https://doi.org/10.5281/zenodo.3733448

University of Illinois/Oklahoma Optical Array Probe (OAP) Processing Software G. M. McFarquhar, J. A. Finlon, D. M. Stechman, W. Wu, R. C. Jackson, and M. Freer https://doi.org/10.5281/zenodo.1285969

Siddhant Gupta et al.

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Short summary
This study evaluates the impact of biomass-burning aerosols on precipitation in marine stratocumulus clouds using observations from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign over the southeast Atlantic. Instances of contact and separation between aerosol and cloud layers show that polluted clouds have lower precipitation rate and lower precipitation susceptibility. This information will help improve cloud representation in Earth system models.
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