CCN measurements during ACE-2 and their relationship to cloud microphysical properties
Author
Chyuang, P.Y.
Collins, D.R.
Jonsson, H.H.
Pawlowska, H.
Snider, J.R.
Brenguier, J.L.
Flagan, Richard C.
Seinfeld, John H.
Date
2000Metadata
Show full item recordAbstract
Measurements of cloud condensation nuclei (CCN) concentration at 0.1% supersaturation were
made onboard the CIRPAS Pelican over the northeast Atlantic during June and July, 1997, in
the vicinity of Tenerife, Spain, as part of the second Aerosol Characterization Experiment
(ACE-2). The average CCN concentration (Nccn) in the marine boundary layer for clean air
masses was 27±8 and 42±14 cm−3 for cloudy and clear conditions, respectively, consistent
with measurements made near the British Isles and close to Tasmania, Australia, during ACE-1
for similar conditions. A local CCN closure experiment was conducted. Measured Nccn is compared
with predictions based on aerosol number size distributions and size-resolved chemical
composition profiles determined from measurements and the literature. A sublinear relationship
between measured and predicted Nccn, Nccn~Nc0c.5n1,predicted, was found. This result is consistent
with some previous studies, but others have obtained results much closer to the expected 1 : 1
relationship between measured and predicted Nccn. A large variability between measured and
predicted Nccn was also observed, leading to the conclusion that, for 95% of the data, the
predictions agree with measurements to within a factor of 11. Relationships between belowcloud
Nccn and aerosol accumulation mode concentration, and in-cloud cloud droplet number
concentration, measured onboard the Pelican and the Me´te´o-France Merlin-IV, respectively,
are calculated for periods while the 2 aircraft were in close proximity at approximately the
same time. Measured relationships are reproduced by an adiabatic parcel model, and are also
consistent with some previous studies. However, the shape of the CCN spectrum, or the aerosol
size distribution, and the updraft velocity are predicted by the model to affect these relationships
to a significant extent. Therefore, parameterizations of cloud microphysical properties need to
include these variables to accurately predict cloud droplet number concentration. A relationship
between Nccn and cloud droplet effective diameter is also calculated and shown to be consistent
both with the literature and with the parameterization of effective diameter proposed by
Martin et al.
Description
Tellus (ACE-2 Special Issue), 52B, 843-867.
Rights
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.Collections
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