Preprints
https://doi.org/10.5194/acp-2021-295
https://doi.org/10.5194/acp-2021-295

  15 Apr 2021

15 Apr 2021

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

Linear relationship between effective radius and precipitation water content near the top of convective clouds

Ramon Campos Braga1, Daniel Rosenfeld2, Ovid O. Krüger1, Barbara Ervens3, Bruna A. Holanda1, Manfred Wendisch4, Trismono Krisna4, Ulrich Pöschl1, Meinrat O. Andreae1,5,6, Christiane Voigt7,8, and Mira L. Pöhlker1 Ramon Campos Braga et al.
  • 1Multiphase Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany
  • 2Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
  • 3Université Clermont Auvergne, CNRS, SIGMA Clermont, Institut de Chimie de Clermont-Ferrand, 63000 Clermont-Ferrand, France
  • 4Leipziger Institut für Meteorologie (LIM), Universität Leipzig, Stephanstr. 3, 04103 Leipzig, Germany
  • 5Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037, USA
  • 6Department of Geology and Geophysics, King Saud University, Riyadh, Saudi Arabia
  • 7Institute of Atmospheric Physics, German Aerospace Center (DLR), 82234 Oberpfaffenhofen, Germany
  • 8Johannes Gutenberg University Mainz, 55099 Mainz, Germany

Abstract. Quantifying the precipitation within clouds is a crucial challenge to improve our current understanding of the Earth’s hydrological cycle. We have investigated the relationship between the effective radius of droplets and ice particles (re) and precipitation water content (PWC) measured by cloud probes near the top of growing convective cumuli. The data for this study were collected by aircraft measurements in clean and polluted conditions over the Amazon Basin and over the western tropical Atlantic in September 2014. Our results indicate a threshold of re ∼ 13 μm for warm rain initiation in convective clouds, which is in agreement with previous studies. In clouds over the Atlantic Ocean, warm rain starts at smaller re, likely linked to the enhancement of coalescence of drops formed on giant cloud condensation nuclei. In cloud passes where precipitation starts as ice hydrometeors, the threshold of re is also shifted to values smaller than 13 μm when coalescence processes are suppressed and precipitating particles are formed by accretion. We found a statistically significant linear relationship between PWC and re for measurements at cloud tops, with a correlation coefficient of ∼0.94. The tight relationship between re and PWC was established only when particles with sizes large enough to precipitate (drizzle and raindrops) are included in calculating re. Our results emphasize for the first time that re is a key parameter to determine both initiation and amount of precipitation at the top of convective clouds.

Ramon Campos Braga et al.

Status: open (until 23 Jun 2021)

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

Ramon Campos Braga et al.

Ramon Campos Braga et al.

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Short summary
Quantifying the precipitation within clouds is crucial for our understanding of the Earth’s hydrological cycle. Using in situ measurements of cloud and rain properties over the Amazon Basin and Atlantic Ocean, we show here a linear relationship between the effective radius (re) and precipitation water content near the tops of convective clouds for different pollution states and temperatures levels. Our results emphasize the role of re to determine both initiation and amount of precipitation.
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