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Published May 22, 2015 | Published
Journal Article Open

Precipitation effects of giant cloud condensation nuclei artificially introduced into stratocumulus clouds


To study the effect of giant cloud condensation nuclei (GCCN) on precipitation processes in stratocumulus clouds, 1–10 μm diameter salt particles (salt powder) were released from an aircraft while flying near the cloud top on 3 August 2011 off the central coast of California. The seeded area was subsequently sampled from the aircraft that was equipped with aerosol, cloud, and precipitation probes and an upward-facing cloud radar. During post-seeding sampling, made 30–60 min after seeding, the mean cloud droplet size increased, the droplet number concentration decreased, and large drop (e.g., diameter larger than 10 μm) concentration increased. Average drizzle rates increased from about 0.05 to 0.20 mm h^(−1), and the liquid water path decreased from about 52 to 43 g m^(−2). Strong radar returns associated with drizzle were observed on the post-seeding cloud-base level-leg flights and were accompanied by a substantial depletion of the cloud liquid water content. The changes were large enough to suggest that the salt particles with concentrations estimated to be 10^(−2) to 10^(-4) cm^(−3) resulted in a four-fold increase in the cloud-base rainfall rate and depletion of the cloud water due to rainout. In contrast, a case is shown where the cloud was already precipitating (on 10 August) and the effect of adding GCCN to the cloud was insignificant.

Additional Information

© Author(s) 2015. This work is distributed under the Creative Commons Attribution 3.0 License. Received: 07 Nov 2014 – Discussion started: 07 Jan 2015 – Revised: 06 Apr 2015 – Accepted: 11 Apr 2015 – Published: 22 May 2015. The E-PEACE field campaign and modeling studies were funded by the National Science Foundation (AGS-1013423; AGS-1008848; AGS-1013381; AGS-1013319; ATM-0744636; AGS-0821599; ATM-0349015) and the Office of Naval Research (N00014-11-1-0783; N00014-10-1-0811; N00014-10-1-0200; N00014-08-1-0465). The authors gratefully acknowledge the crew of the CIRPAS Twin Otter for their assistance during the field campaign and Daniel Rosenfeld for providing the powdered salt. We also appreciate the outstanding efforts of Tom Snowdon on the design and fabrication of the salt-powder dispensing system. We greatly appreciate the thoughtful comments provided by the reviewer Jorgen Jensen. Edited by: L. Zhang

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