Articles | Volume 17, issue 23
Atmos. Chem. Phys., 17, 14727–14746, 2017

Special issue: The ACRIDICON-CHUVA campaign to study deep convective clouds...

Special issue: BACCHUS – Impact of Biogenic versus Anthropogenic emissions...

Special issue: Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5)...

Atmos. Chem. Phys., 17, 14727–14746, 2017
Research article
11 Dec 2017
Research article | 11 Dec 2017

Illustration of microphysical processes in Amazonian deep convective clouds in the gamma phase space: introduction and potential applications

Micael A. Cecchini1,6, Luiz A. T. Machado1, Manfred Wendisch2, Anja Costa3, Martina Krämer3, Meinrat O. Andreae4,5, Armin Afchine3, Rachel I. Albrecht6, Paulo Artaxo7, Stephan Borrmann4,8, Daniel Fütterer9, Thomas Klimach4, Christoph Mahnke4,8, Scot T. Martin10, Andreas Minikin9,11, Sergej Molleker8, Lianet H. Pardo1, Christopher Pöhlker4, Mira L. Pöhlker4, Ulrich Pöschl4, Daniel Rosenfeld12, and Bernadett Weinzierl9,13,14 Micael A. Cecchini et al.
  • 1Centro de Previsão de Tempo e Estudos Climáticos, Instituto Nacional de Pesquisas Espaciais, Cachoeira Paulista, Brazil
  • 2Leipziger Institut für Meteorologie (LIM), Universität Leipzig, Stephanstr. 3, 04103 Leipzig, Germany
  • 3Forschungszentrum Jülich, Institut für Energie und Klimaforschung (IEK-7), Jülich, Germany
  • 4Biogeochemistry, Multiphase Chemistry, and Particle Chemistry Departments, Max Planck Institute for Chemistry, P.O. Box 3060, 55020 Mainz, Germany
  • 5Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92037, USA
  • 6Departamento de Ciências Atmosféricas, Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG), Universidade de São Paulo (USP), São Paulo, Brazil
  • 7Instituto de Física (IF), Universidade de São Paulo (USP), São Paulo, Brazil
  • 8Institut für Physik der Atmosphäre (IPA), Johannes Gutenberg-Universität, Mainz, Germany
  • 9Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, 82234 Wessling, Germany
  • 10School of Engineering and Applied Sciences and Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
  • 11Flugexperimente, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany
  • 12Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
  • 13Faculty of Physics, University of Vienna, Boltzmanngasse 5, 1090 Vienna, Austria
  • 14Ludwig-Maximilians-Universität, Meteorologisches Institut, Munich, Germany

Abstract. The behavior of tropical clouds remains a major open scientific question, resulting in poor representation by models. One challenge is to realistically reproduce cloud droplet size distributions (DSDs) and their evolution over time and space. Many applications, not limited to models, use the gamma function to represent DSDs. However, even though the statistical characteristics of the gamma parameters have been widely studied, there is almost no study dedicated to understanding the phase space of this function and the associated physics. This phase space can be defined by the three parameters that define the DSD intercept, shape, and curvature. Gamma phase space may provide a common framework for parameterizations and intercomparisons. Here, we introduce the phase space approach and its characteristics, focusing on warm-phase microphysical cloud properties and the transition to the mixed-phase layer. We show that trajectories in this phase space can represent DSD evolution and can be related to growth processes. Condensational and collisional growth may be interpreted as pseudo-forces that induce displacements in opposite directions within the phase space. The actually observed movements in the phase space are a result of the combination of such pseudo-forces. Additionally, aerosol effects can be evaluated given their significant impact on DSDs. The DSDs associated with liquid droplets that favor cloud glaciation can be delimited in the phase space, which can help models to adequately predict the transition to the mixed phase. We also consider possible ways to constrain the DSD in two-moment bulk microphysics schemes, in which the relative dispersion parameter of the DSD can play a significant role. Overall, the gamma phase space approach can be an invaluable tool for studying cloud microphysical evolution and can be readily applied in many scenarios that rely on gamma DSDs.

Short summary
This study introduces and explores the concept of gamma phase space. This space is able to represent all possible variations in the cloud droplet size distributions (DSDs). The methodology was applied to recent in situ aircraft measurements over the Amazon. It is shown that the phase space is able to represent several processes occurring in the clouds in a simple manner. The consequences for cloud studies, modeling, and the representation of the transition from warm to mixed phase are discussed.
Final-revised paper