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Aerosol–cloud drop concentration closure in warm cumulus

Conant, W. C. and VanReken, T. M. and Rissman, T. A. and Varutbangkul, V. and Jonsson, H. H. and Nenes, A. and Jimenez, J. L. and Delia, A. E. and Bahreini, R. and Roberts, G. C. and Flagan, R. C. and Seinfeld, J. H. (2004) Aerosol–cloud drop concentration closure in warm cumulus. Journal of Geophysical Research. Atmospheres, 109 (D13). Art. No. D13204. ISSN 2169-897X. doi:10.1029/2003JD004324.

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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.

Item Type:Article
Related URLs:
URLURL TypeDescription
VanReken, T. M.0000-0002-2645-4911
Jonsson, H. H.0000-0003-3043-1074
Nenes, A.0000-0003-3873-9970
Jimenez, J. L.0000-0001-6203-1847
Roberts, G. C.0000-0002-3636-8590
Flagan, R. C.0000-0001-5690-770X
Seinfeld, J. H.0000-0003-1344-4068
Additional Information:Copyright 2004 by the American Geophysical Union. Received 3 November 2003; revised 29 April 2004; accepted 14 May 2004; published 14 July 2004. This work was supported by National Aeronautics and Space Administration grant NAG5-11549 and the Office of Naval Research.
Funding AgencyGrant Number
Office of Naval Research (ONR)UNSPECIFIED
Subject Keywords:aerosol; CCN; cloud microphysics
Issue or Number:D13
Classification Code:0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 1610 Global Change
Record Number:CaltechAUTHORS:20141028-093136295
Persistent URL:
Official Citation:Conant, W. C., et al. (2004), Aerosol–cloud drop concentration closure in warm cumulus, J. Geophys. Res., 109, D13204, doi:10.1029/2003JD004324.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:50918
Deposited By: George Porter
Deposited On:28 Oct 2014 16:52
Last Modified:10 Nov 2021 19:02

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