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AGU: Journal of Geophysical Research, Atmospheres

 

Keywords

  • aerosol
  • CCN
  • cloud microphysics

Index Terms

  • Atmospheric Composition and Structure: Aerosols and particles
  • Atmospheric Composition and Structure: Cloud physics and chemistry
  • Atmospheric Composition and Structure: Pollution—urban and regional
  • Global Change: Atmosphere
  • Meteorology and Atmospheric Dynamics: Convective processes
Abstract
Cited By (24)
 

Abstract

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 109, D13204, 12 PP., 2004
doi:10.1029/2003JD004324

Aerosol–cloud drop concentration closure in warm cumulus

W. C. Conant

Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, California, USA

T. M. VanReken

Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

T. A. Rissman

Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

V. Varutbangkul

Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

H. H. Jonsson

Center for Interdisciplinary Remotely-Piloted Aircraft Studies, Naval Postgraduate School, Monterey, California, USA

A. Nenes

Schools of Earth and Atmospheric Sciences and Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, USA

J. L. Jimenez

Department of Chemistry and Biochemistry, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA

A. E. Delia

Program in Atmospheric and Oceanic Sciences, University of Colorado, Boulder, Colorado, USA

R. Bahreini

Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, California, USA

G. C. Roberts

Center for Atmospheric Sciences, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California, USA

R. C. Flagan

Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, California, USA

Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

J. H. Seinfeld

Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, California, USA

Department of Chemical Engineering, California Institute of Technology, Pasadena, California, USA

Our understanding of the activation of aerosol particles into cloud drops during the formation of warm cumulus clouds presently has a limited observational foundation. Detailed observations of aerosol size and composition, cloud microphysics and dynamics, and atmospheric thermodynamic state were collected in a systematic study of 21 cumulus clouds by the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft during NASA's Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment (CRYSTAL-FACE). An “aerosol-cloud” closure study was carried out in which a detailed cloud activation parcel model, which predicts cloud drop concentration using observed aerosol concentration, size distribution, cloud updraft velocity, and thermodynamic state, is evaluated against observations. On average, measured droplet concentration in adiabatic cloud regions is within 15% of the predictions. This agreement is corroborated by independent measurements of aerosol activation carried out by two cloud condensation nucleus (CCN) counters on the aircraft. Variations in aerosol concentration, which ranged from 300 to 3300 cm−3, drives large microphysical differences (250–2300 cm−3) observed among continental and maritime clouds in the South Florida region. This is the first known study in which a cloud parcel model is evaluated in a closure study using a constraining set of data collected from a single platform. Likewise, this is the first known study in which relationships among aerosol size distribution, CCN spectrum, and cloud droplet concentration are all found to be consistent with theory within experimental uncertainties much less than 50%. Vertical profiles of cloud microphysical properties (effective radius, droplet concentration, dispersion) clearly demonstrate the boundary layer aerosol's effect on cloud microphysics throughout the lowest 1 km of cloud depth. Onboard measurements of aerosol hygroscopic growth and the organic to sulfate mass ratio are related to CCN properties. These chemical data are used to quantify the range of uncertainty associated with the simplified treatment of aerosol composition assumed in the closure study.

Received 3 November 2003; accepted 14 May 2004; published 14 July 2004.

Citation: Conant, W. C., et al. (2004), Aerosol–cloud drop concentration closure in warm cumulus, J. Geophys. Res., 109, D13204, doi:10.1029/2003JD004324.

Cited By

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