The rime-splintering hypothesis of cumulus glaciation examined using a field-of-flow cloud model

Abstract

A mathematical experiment was conducted to test the hypothesis that the occurrence of unexpectedly large concentrations of ice particles in certain clouds is caused by the production of small ice particles (‘splinters’) during the riming of mother ice particles. the experiment used an axially symmetric two-dimensional field-of-flow model incorporating parameterized liquid and ice microphysics. the behaviour of clouds, growing with either wide or narrow initial droplet size distributions, with and without splintering, was simulated. Splintering criteria were based on recent laboratory data. The rapidity of liquid to ice conversion was found to be a strong, direct function of the prior presence of large liquid drops. the dynamical properties of the clouds influenced both splinter production and also the over-all glaciating characteristics regardless of the presence or absence of an ‘ice multiplication’ mechanism. Cloud condensate at levels having strong updraughts and vigorous growth was more slowly converted to ice than condensate in regions of dissipating cloud. the simulations permitting ice generation by splintering more closely duplicated pertinent observations in nature than those without splinter production. Unexpectedly, the characteristics of the liquid phase exerted substantial influence on the dynamics of the simulated clouds.