Explosive ice multiplication by mechanical breakup in iceice collisions: A dynamical systembased study
Forskningsoutput: Tidskriftsbidrag › Artikel i vetenskaplig tidskrift
Abstract
Mechanical breakup in iceice collisions observed in the laboratory can lead to explosive ice multiplication. The possibility is examined in detail by constructing an idealized analytical singlepoint (zerodimension) model assuming spatial homogeneity within a cloud. The rate of generation of primary ice is fixed at a constant value over time, corresponding to a situation in which the relative humidity (at water saturation as for a mixedphase cloud) and updraught speed are fixed. This would further imply an infinite supply of vapour, if the crystal concentration were somehow infinite. Fixed times are assumed for the transformation of the generated primary ice into small graupel, which then grow into large graupel. Secondary ice particles produced by collisions between small and large graupel, in turn, potentially multiply explosively, because the secondary ice may eventually grow to become splintering graupel with a positive feedback. Two basic processes can lead to explosive ice multiplication. The first process is the generation of primary ice, which initiates ice multiplication only with a relatively low threshold (∼10^{4} m^{3} s^{1}) compared to typical observed values for deep convective clouds. Then the second process is induced by a sufficiently large initial number of ice crystals, which generate enough both small and large graupel particles, leading to explosive multiplication, even when the rate of generation of primary ice is below the threshold. These initial crystals at supercritical amounts may be from any source. Only a low number density of crystals of the order of 1 m^{3} (or 10^{3} l^{1}) is required initially. In both cases, the ice number literally explodes within a finite time, with a timescale from 30 to 200 min under the idealized singlepoint model studied. Importantly, in real clouds a typical number density of large graupel is above the threshold needed for explosive breakup.
Detaljer
Författare  

Enheter & grupper  
Externa organisationer 

Forskningsområden  Ämnesklassifikation (UKÄ) – OBLIGATORISK
Nyckelord 
Originalspråk  engelska 

Sidor (fråntill)  867879 
Antal sidor  13 
Tidskrift  Quarterly Journal of the Royal Meteorological Society 
Volym  142 
Utgåva nummer  695 
Status  Published  2016 jan 1 
Publikationskategori  Forskning 
Peer review utförd  Ja 