Articles | Volume 17, issue 12
Atmos. Chem. Phys., 17, 7365–7386, 2017

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

Atmos. Chem. Phys., 17, 7365–7386, 2017

Research article 20 Jun 2017

Research article | 20 Jun 2017

Comparing parameterized versus measured microphysical properties of tropical convective cloud bases during the ACRIDICON–CHUVA campaign

Ramon Campos Braga1, Daniel Rosenfeld2, Ralf Weigel3, Tina Jurkat4, Meinrat O. Andreae5,9, Manfred Wendisch6, Mira L. Pöhlker5, Thomas Klimach5, Ulrich Pöschl5, Christopher Pöhlker5, Christiane Voigt3,4, Christoph Mahnke3, Stephan Borrmann3, Rachel I. Albrecht7, Sergej Molleker8, Daniel A. Vila1, Luiz A. T. Machado1, and Paulo Artaxo10 Ramon Campos Braga et al.
  • 1Centro de Previsão de Tempo e Estudos Climáticos, Instituto Nacional de Pesquisas Espaciais, Cachoeira Paulista, Brasil
  • 2Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
  • 3Institut für Physik der Atmosphäre, Johannes Gutenberg-Universität, Mainz, Germany
  • 4Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany
  • 5Multiphase Chemistry and Biogeochemistry Departments, Max Planck Institute for Chemistry, 55020 Mainz, Germany
  • 6Leipziger Institut für Meteorologie (LIM), Universität Leipzig, Stephanstr. 3, 04103 Leipzig, Germany
  • 7Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, São Paulo, Brazil
  • 8Max Planck Institute for Chemistry (MPI), Particle Chemistry Department, Mainz, Germany
  • 9Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92037, USA
  • 10Instituto de Física (IF), Universidade de São Paulo (USP), São Paulo, Brazil

Abstract. The objective of this study is to validate parameterizations that were recently developed for satellite retrievals of cloud condensation nuclei supersaturation spectra, NCCN(S), at cloud base alongside more traditional parameterizations connecting NCCN(S) with cloud base updrafts and drop concentrations. This was based on the HALO aircraft measurements during the ACRIDICON–CHUVA campaign over the Amazon region, which took place in September 2014. The properties of convective clouds were measured with a cloud combination probe (CCP), a cloud and aerosol spectrometer (CAS-DPOL), and a CCN counter onboard the HALO aircraft. An intercomparison of the cloud drop size distributions (DSDs) and the cloud water content (CWC) derived from the different instruments generally shows good agreement within the instrumental uncertainties. To this end, the directly measured cloud drop concentrations (Nd) near cloud base were compared with inferred values based on the measured cloud base updraft velocity (Wb) and NCCN(S) spectra. The measurements of Nd at cloud base were also compared with drop concentrations (Na) derived on the basis of an adiabatic assumption and obtained from the vertical evolution of cloud drop effective radius (re) above cloud base. The measurements of NCCN(S) and Wb reproduced the observed Nd within the measurements uncertainties when the old (1959) Twomey's parameterization was used. The agreement between the measured and calculated Nd was only within a factor of 2 with attempts to use cloud base S, as obtained from the measured Wb, Nd, and NCCN(S). This underscores the yet unresolved challenge of aircraft measurements of S in clouds. Importantly, the vertical evolution of re with height reproduced the observation-based nearly adiabatic cloud base drop concentrations, Na. The combination of these results provides aircraft observational support for the various components of the satellite-retrieved methodology that was recently developed to retrieve NCCN(S) under the base of convective clouds. This parameterization can now be applied with the proper qualifications to cloud simulations and satellite retrievals.

Final-revised paper