Mechanistic limitations to the release of latent heat during the natural and artificial glaciation of deep convective clouds

Abstract

S U M M A R YThe 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. Present affiliation: Joseph Oat Cow.. Camden. NJ 08104, USA.

Aerosol control on depth of warm rain in convective clouds

“…Initiation of precipitation may also be triggered by cold processes [e.g., Lamb et al , 1981], but here we limit our study to the warm rain process where precipitation was initiated as raindrops, even when T* < 0°C, where rain initiates as supercooled water. We investigated here relationship between the N CCN at 0.4% SS (N 0.4% ) below the cloud base and N c above cloud base.…”

Factors controlling secondary ice production in cumulus clouds

“…It is well known that supercooled raindrops play an important role in the ice process (e.g. Koenig, ; Lamb et al , ; Phillips et al , ). The model results herein are consistent with those of Chisnell and Latham () and Blyth and Latham ().…”

“…Results of calculations performed by Chisnell and Latham () showed that supercooled raindrops can play an important role in the glaciation of clouds by the HM rime‐splinter mechanism because instant rimers are produced when the raindrops freeze. Later modelling studies by, for example, Koenig (), Lamb et al (), Phillips et al (), Sun et al () and Crawford et al () further illustrated the importance of supercooled raindrops in the HM multiplication process. In addition, Chisnell and Latham () found that the rate of glaciation may be substantially enhanced if the raindrops themselves produced splinters as they froze.…”

Aerosol Effects on Microstructure and Intensity of Tropical Cyclones

“…It is now understood that the amount of supercooled water in the TCs is too small to expect much of a seeding effect upon freezing, and this small amount of water freezes naturally quickly above the 0°C level. As shown in several modeling studies (Cotton 1972;Koenig and Murray 1976;Scott and Hobbs 1977), the presence of these large drops enhances the rapidity of glaciation of clouds and also produces greater concentrations of ice particles by the rime-splinter ice multiplication process (Hallett and Mossop 1974;Koenig 1977;Lamb et al 1981). Much of the rain precipitates without ever freezing (e.g., Khain et al 2008a;).…”