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Science 30 April 2004:
Vol. 304. no. 5671, pp. 718 - 722
DOI: 10.1126/science.1094947
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Reports

Evidence for the Predominance of Mid-Tropospheric Aerosols as Subtropical Anvil Cloud Nuclei

Ann M. Fridlind,1* Andrew S. Ackerman,1 Eric J. Jensen,1 Andrew J. Heymsfield,2 Michael R. Poellot,3 David E. Stevens,4 Donghai Wang,5 Larry M. Miloshevich,2 Darrel Baumgardner,6 R. Paul Lawson,7 James C. Wilson,8 Richard C. Flagan,9 John H. Seinfeld,9 Haflidi H. Jonsson,10 Timothy M. VanReken,9 Varuntida Varutbangkul,9 Tracey A. Rissman9

NASA's recent Cirrus Regional Study of Tropical Anvils and Cirrus Layers–Florida Area Cirrus Experiment focused on anvil cirrus clouds, an important but poorly understood element of our climate system. The data obtained included the first comprehensive measurements of aerosols and cloud particles throughout the atmospheric column during the evolution of multiple deep convective storm systems. Coupling these new measurements with detailed cloud simulations that resolve the size distributions of aerosols and cloud particles, we found several lines of evidence indicating that most anvil crystals form on mid-tropospheric rather than boundary-layer aerosols. This result defies conventional wisdom and suggests that distant pollution sources may have a greater effect on anvil clouds than do local sources.

1 National Aeronautics and Space Administration (NASA) Ames Research Center, Moffett Field, CA 94035, USA.
2 National Center for Atmospheric Research, Boulder, CO 80307, USA.
3 Department of Atmospheric Sciences, University of North Dakota, Grand Forks, ND 58202, USA.
4 Lawrence Livermore National Laboratory, Livermore, CA 94552, USA.
5 Center for Atmospheric Sciences, Hampton University and NASA Langley Research Center, Hampton, VA 23681, USA.
6 Centro de Ciencias de la Atmosfera, Universidad Nacional Autonoma de Mexico, Mexico City, DF 04510, Mexico.
7 Stratton Park Engineering Company, Inc., Boulder, CO 80301, USA.
8 Department of Engineering, University of Denver, Denver, CO 80208, USA.
9 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA.
10 Center for Interdisciplinary Remotely-Piloted Aircraft Studies, Marina, CA 93933, USA.

* To whom correspondence should be addressed. E-mail: ann.fridlind{at}nasa.gov

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