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Mechanistic limitations to the release of latent heat during the natural and artificial glaciation of deep convective clouds
Author(s) -
Lamb Dennis,
Hallett John,
Sax R. I.
Publication year - 1981
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49710745412
Subject(s) - ice nucleus , seeding , glacial period , supercooling , latent heat , nucleation , atmospheric sciences , geology , materials science , environmental science , meteorology , thermodynamics , physics , geomorphology
The latent heat thermodynamically available in the supercooled water of deep convective clouds is released at rates governed by the glaciation mechanism, presumed here to involve primary nucleation, capture nucleation of rain by small ice particles and secondary ice production (rime‐splintering hypothesis). A simple microphysical model of the glaciation shows the importance of regenerative feed‐back on the evolution of ice when the primary nucleation and regenerative processes proceed simultaneously, leading to insensitivity to the primary ice nucleus concentration. This allows rapid glaciation and heat release to occur naturally in clouds exhibiting a broad supercooled drop size spectrum. New observational data and model results of artificially induced glaciation are consistent with the idea that the primary microphysical role of seeding is the creation of many small ice particles which substitute for the secondary ice splinters of naturally induced glaciation. the aerodynamic capture of the splinters by the supercooled rain leads to the formation of new graupel particles and the rapid release of fusional heat, shown by calculation to dominate the heat release mechanisms. With a seeding agent acting in the contact mode the small (cloud drop) end of the spectrum is required, since Brownian scavenging of the nuclei by the few large rain drops is inefficient. the quantitative analysis of these glaciation concepts also demonstrates that realistic seeding under conditions conducive to ice multiplication could increase materially the rate of heat release and offer opportunities for artificially invigorating the dynamic structure of a cloud if glaciation is induced to occur within a relatively narrow ‘time window’ for seeding.