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Laboratory simulations show diabatic heating drives cumulus-cloud evolution and entrainment

Narasimha, Roddam and Diwan, Sourabh Suhas and Duvvuri, Subrahmanyam and Sreenivasan, K. R. and Bhat, G. S. (2011) Laboratory simulations show diabatic heating drives cumulus-cloud evolution and entrainment. Proceedings of the National Academy of Sciences of the United States of America, 108 (39). pp. 16164-16169. ISSN 0027-8424. PMCID PMC3182732.

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Clouds are the largest source of uncertainty in climate science, and remain a weak link in modeling tropical circulation. A major challenge is to establish connections between particulate microphysics and macroscale turbulent dynamics in cumulus clouds. Here we address the issue from the latter standpoint. First we show how to create bench-scale flows that reproduce a variety of cumulus-cloud forms (including two genera and three species), and track complete cloud life cycles—e.g., from a “cauliflower” congestus to a dissipating fractus. The flow model used is a transient plume with volumetric diabatic heating scaled dynamically to simulate latent-heat release from phase changes in clouds. Laser-based diagnostics of steady plumes reveal Riehl–Malkus type protected cores. They also show that, unlike the constancy implied by early self-similar plume models, the diabatic heating raises the Taylor entrainment coefficient just above cloud base, depressing it at higher levels. This behavior is consistent with cloud-dilution rates found in recent numerical simulations of steady deep convection, and with aircraft-based observations of homogeneous mixing in clouds. In-cloud diabatic heating thus emerges as the key driver in cloud development, and could well provide a major link between microphysics and cloud-scale dynamics.

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Duvvuri, Subrahmanyam0000-0001-8082-1658
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Additional Information:Copyright © 2015 National Academy of Sciences. We thank Professor M. R. S. Rao, President of Jawaharlal Nehru Centre for Advanced Scientific Research for a grant toward this project, and many students in the Fluid Dynamics Lab for their help during the experiments. We acknowledge useful discussions with Dr. S. R. Rajagopalan and Dr. L. Venkatakrishnan of National Aerospace Laboratories, Bangalore and with Prof. O. N. Ramesh of Deparment of Aerospace Engineering, Indian Institute of Science, Bangalore. R.N. thanks the Centre for Atmospheric and Oceanic Sciences, IISc for their continued hospitality. Author contributions: R.N., S.D., K.R.S., and G.S.B. designed research; R.N., S.S.D., S.D., and G.S.B. performed research; S.S.D. and K.R.S. contributed new reagents/analytic tools; R.N., S.S.D., and K.R.S. analyzed data; and R.N., S.S.D., K.R.S., and G.S.B. wrote the paper. The authors declare no conflict of interest. This article contains supporting information online at
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Jawaharlal Nehru Centre for Advanced Scientific ResearchUNSPECIFIED
Subject Keywords:cloud fluid dynamics; off-source heating; anomalous entrainment; turbulent mixing
Issue or Number:39
PubMed Central ID:PMC3182732
Record Number:CaltechAUTHORS:20150402-092452262
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Official Citation:Roddam Narasimha, Sourabh Suhas Diwan, Subrahmanyam Duvvuri, K. R. Sreenivas, and G. S. Bhat Laboratory simulations show diabatic heating drives cumulus-cloud evolution and entrainment PNAS 2011 108 (39) 16164-16169; published ahead of print September 14, 2011, doi:10.1073/pnas.1112281108
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56305
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Deposited On:02 Apr 2015 20:43
Last Modified:02 Jun 2020 20:45

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