Polluting of winter convective clouds upon transition from ocean inland over central California: contrasting case studies
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Authors
Rosenfeld, Daniel
Chemke, Rei
Prather, Kimberly
Suski, Kaitlyn
Comstock, Jennifer M.
Schmid, Beat
Tomlinson, Jason
Jonsson, Haflidi
Subjects
Cloud-aerosol interactions
Precipitation suppression
Precipitation suppression
Advisors
Date of Issue
2014
Date
Publisher
Elsevier
Language
Abstract
In-situ aircraft measurements of aerosol chemical and cloud microphysical properties were conducted during the CalWater campaign in February and March 2011 over the Sierra Nevada Mountains and the coastal waters of central California. The main objective was to elucidate the impacts of aerosol properties on clouds and precipitation forming processes. In order to accomplish this, we compared contrasting cases of clouds that ingested aerosols from different sources. The results showed that clouds containing pristine oceanic air had low cloud drop concentrations and started to develop rain 500 m above their base. This occurred both over the ocean and over the Sierra Nevada, mainly in the early morning when the radiatively cooled stable continental boundary layer was decoupled from the cloud base. Supercooled rain dominated the precipitation that formed in growing convective clouds in the pristine air, up to the −21 °C isotherm level. A contrasting situation was documented in the afternoon over the foothills of the Sierra Nevada, when the clouds ingested high pollution aerosol concentrations produced in the Central Valley. This led to slow growth of the cloud drop effective radius with height and suppressed and even prevented the initiation of warm rain while contributing to the development of ice hydrometeors in the form of graupel. Our results show that cloud condensation and ice nuclei were the limiting factors that controlled warm rain and ice processes, respectively, while the unpolluted clouds in the same air mass produced precipitation quite efficiently. These findings provide the motivation for deeper investigations into the nature of the aerosols seeding clouds.
Type
Article
Description
The article of record as published may be found at: http://dx.doi.org/10.1016/j.atmosres.2013.09.006
Series/Report No
Department
Identifiers
NPS Report Number
Sponsors
Funder
Format
Citation
Atmospheric Research, v.135/136, 2014, pp. 112-127
Distribution Statement
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.