Preprints
https://doi.org/10.5194/acp-2021-80
https://doi.org/10.5194/acp-2021-80

  16 Mar 2021

16 Mar 2021

Review status: a revised version of this preprint is currently under review for the journal ACP.

Cloud droplet number closure for tropical convective clouds during the ACRIDICON–CHUVA campaign

Ramon Campos Braga1, Barbara Ervens2, Daniel Rosenfeld3, Meinrat O. Andreae4,5, Jan-David Förster1, Daniel Fütterer6, Lianet Hernández Pardo1, Bruna A. Holanda1, Tina Jurkat6, Ovid O. Krüger1, Oliver Lauer1, Luiz A. T. Machado1,7, Christopher Pöhlker1, Daniel Sauer6, Christiane Voigt6,8, Adrian Walser6, Manfred Wendisch9, Ulrich Pöschl1, and Mira L. Pöhlker1 Ramon Campos Braga et al.
  • 1Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 2Université Clermont Auvergne, CNRS, SIGMA Clermont, Institut de Chimie de Clermont-Ferrand, 63000 Clermont-Ferrand, France
  • 3Institute of Earth Sciences, The Hebrew University of Jerusalem, 9190401 Jerusalem, Israel
  • 4Biogeochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 5Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037, USA
  • 6Institute of Atmospheric Physics, German Aerospace Center (DLR), 82234 Oberpfaffenhofen, Germany
  • 7National Institute for Space Research (INPE), 12227-010 São José Dos Campos, Brazil
  • 8Johannes Gutenberg University Mainz, 55099 Mainz, Germany
  • 9Faculty of Physics and Earth Sciences, Leipzig Institute for Meteorology, University of Leipzig, 04103 Leipzig, Germany

Abstract. The main objective of the ACRIDICON-CHUVA (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the Global Precipitation measurements) campaign in September 2014 was the investigation of aerosol-cloud-interactions in the Amazon Basin. Cloud properties near cloud base of growing convective cumuli were characterized by cloud droplet size distribution measurements using a cloud combination probe (CCP) and a cloud and aerosol spectrometer (CAS-DPOL). In the current study, an adiabatic parcel model was used to perform cloud droplet number (Nd) closure studies for several flights in differently polluted air masses. Model input parameters included aerosol size distributions, measured with an ultra-high sensitive aerosol spectrometer (UHSAS), in combination with a condensation particle counter (CPC). Updraft speeds (w) were measured near cloud base using a boom-mounted Rosemount model 858 AJ probe. To compare to model predictions, measured Nd and w were statistically matched based on equal percentiles of occurrence. Reasonable agreement between measured and predicted Nd was achieved when a particle hygroscopicity of κ ~ 0.1 is assumed. Similar closure results were obtained when the variability in the particle number concentration was taken into account. We conclude that Nd can be predicted using a single κ, and measured aerosol particle number concentration below cloud base when w is constrained based on measurements. In accordance with previous adiabatic air parcel model studies, the largest disagreements between predicted and measured Nd were found when updraft speeds were high (w > 2.5 m s−1) or in the presence of a bimodal aerosol size distribution. We show that simplifying assumptions on κ might not be appropriate when the aerosol size distribution is comprised of both distinct Aitken and accumulation modes, as predicted Nd clearly deviate from measured ones at w ≥ 1 m s−1 which points to a contribution of Aitken mode particles to Nd.

Ramon Campos Braga et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-80', Anonymous Referee #1, 13 Apr 2021
  • RC2: 'Comment on acp-2021-80', Anonymous Referee #2, 16 Apr 2021

Ramon Campos Braga et al.

Ramon Campos Braga et al.

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Short summary
Interactions of aerosol particles with clouds represent a large uncertainty in estimates of climate change. Properties of aerosol particles control their ability to act as cloud condensation nuclei. Using aerosol measurements in the Amazon, we performed model studies to compare predicted and measured cloud droplet number concentrations at cloud bases. Our results confirm previous estimates of particle hygroscopicity in this region.
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