Slippery thermals and the cumulus entrainment paradox Sherwood, Steven en_US Hernandez-Deckers, Daniel en_US Robinson, F en_US Colin, M en_US 2021-11-25T12:29:59Z 2021-11-25T12:29:59Z 2013 en_US
dc.description.abstract In numerical simulations of growing congestus clouds, the maximum upward velocities w typically occur in compact toroidal vortices or thermals. These maxima were tracked, and the momentum budget was analyzed within spherical regions centered on them with objectively determined radii approximately enclosing the vortex ring or pair. Such regions are proposed as an advantageous prototype for rising air parcels due to their prolonged identity as evident in laboratory flows. Buoyancy and other forces are generally less than 0.02 m s(-2) (0.7 K). In particular, resolved mixing between thermals and their environment fails to produce the drag normally anticipated, often producing even a slight upward force, indicating that parcel models should allow for significantly different dilution rates for momentum than for material properties. A conceptual model is proposed to explain this as a result of the thermals' internal circulation and detrainment characteristics.The implications of momentum dilution for cumulus development are explored using a simple model of a heterogeneous entraining parcel. Without friction, parcels reach the upper troposphere even at a high entrainment rate [similar to(2 km)(-1)] if the environment is sufficiently humid, whereas with standard momentum dilution, a much lower entrainment rate is required. Peak condensed water amounts and sensitivities of cloud amount and height to ambient humidity are significantly more realistic in the high-entrainment case. This suggests that revised treatments of friction and momentum could help address the entrainment paradox whereby entrainment rates implied by detailed cloud studies are higher than those typically preferred for parcel-based calculations. en_US
dc.identifier.issn 0022-4928 en_US
dc.language English
dc.language.iso EN en_US
dc.rights CC BY-NC-ND 3.0 en_US
dc.rights.uri en_US
dc.source Legacy MARC en_US
dc.title Slippery thermals and the cumulus entrainment paradox en_US
dc.type Journal Article en
dcterms.accessRights open access
dspace.entity.type Publication en_US
unsw.description.publisherStatement © Copyright (2013) American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at ( or from the AMS at 617-227-2425 or en_US
unsw.identifier.doiPublisher en_US
unsw.relation.FunderRefNo DYN078550 en_US
unsw.relation.faculty Science
unsw.relation.fundingScheme NSF Physical and Dynamical Meteorology program en_US
unsw.relation.ispartofissue 8 en_US
unsw.relation.ispartofjournal Journal of the Atmospheric Sciences en_US
unsw.relation.ispartofpagefrompageto 2426-2442 en_US
unsw.relation.ispartofvolume 70 en_US
unsw.relation.originalPublicationAffiliation Sherwood, Steven, Climate Change Research Centre (CCRC), Faculty of Science, UNSW en_US
unsw.relation.originalPublicationAffiliation Hernandez-Deckers, Daniel, Climate Change Research Centre (CCRC), Faculty of Science, UNSW en_US
unsw.relation.originalPublicationAffiliation Robinson, F en_US
unsw.relation.originalPublicationAffiliation Colin, M, Climate Change Research Centre (CCRC), Faculty of Science, UNSW en_US School of Biological, Earth & Environmental Sciences *
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