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Measurements of cloud condensation nuclei spectra within maritime cumulus cloud droplets: Implications for mixing processesIn a cloud formed during adiabatic expansion, the droplet size distribution will be systematically related to the critical supersaturation of the cloud condensation nuclei (CNN), but this relationship can be complicated in entraining clouds. Useful information about cloud processes, such as mixing, can be obtained from direct measurements of the CNN involved in droplet nucleation. This was accomplished by interfacing two instruments for a series of flights in maritime cumulus clouds. One instrument, the counterflow virtual impactor, collected cloud droplets, and the nonvolatile residual nuclei of the droplets was then passed to a CCN spectrometer, which measured the critical supersaturation (S(sub c)) spectrum of the droplet nuclei. The measured S(sub c) spectra of the droplet nuclei were compared with the S(sub c) spectra of ambient aerosol particles in order to identify which CCN were actually incorporated into droplets and to determine when mixing processes were active at different cloud levels. The droplet nuclei nearly always exhibited lower median S(sub c)'s than the ambient aerosol, as expected since droplets nucleate perferentially on particles with lower critical supersaturations. Critical supersaturation spectra from nuclei of droplets near cloud base were similar to those predicted for cloud regions formed adiabatically, but spectra of droplet nuclei from middle cloud levels showed some evidence that mixing had occurred. Near cloud top, the greatest variation in the spectra of the droplet nuclei was observed, and nuclei with high S(sub c)'s were sometimes present even within relatively large droplets. This suggests that the extent of mixing increases with height in cumulus clouds and that inhomogeneous mixing may be important near cloud top. These promising initial results suggest improvements to the experimental technique that will permit more quantitative results in future experiments.
Document ID
19950045337
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Twohy, Cynthia H.
(National Center for Atmospheric Research, Boulder, CO United States)
Hudson, James G.
(Atmospheric Sciences Center Desert Research Inst., Reno, NV, United States)
Date Acquired
August 16, 2013
Publication Date
April 1, 1995
Publication Information
Publication: Journal of Applied Meteorology
Volume: 34
Issue: 4
ISSN: 0894-8763
Subject Category
Meteorology And Climatology
Accession Number
95A76936
Funding Number(s)
CONTRACT_GRANT: N00014-91-J-1090
CONTRACT_GRANT: NSF ATM-92-09181
CONTRACT_GRANT: NSF ATM-89-19935
Distribution Limits
Public
Copyright
Other

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