Aerosol-Cloud drop concentration closure in warm cumulus
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Authors
Rissman, T.A.
Varutbangkul, V.
Jonsson, H.H.
Nenes, A.
Jimenez, J.L.
Delia, A.E.
Bahreini, R.
Roberts, G.C.
Seinfled, J.H.
Conant, W. C.
Subjects
aerosol
CCN
cloud microphysics
CCN
cloud microphysics
Advisors
Date of Issue
2004
Date
2004
Publisher
Language
Abstract
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.
Type
Description
Journal of Geophysical Research, Vol. 109, D13204
The article of record as published may be located at http://dx.doi.org/10.1029/2003JD004324
The article of record as published may be located at http://dx.doi.org/10.1029/2003JD004324
Series/Report No
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Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS)
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This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.