Hallet-Mossop Process as a
Mechanism for Ice Multiplication
Steven Brown
Atmospheric Sciences
5/16/2011
Outline
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Role of Ice Particles in precipitation
Evidence for Ice Multiplication
What is the Hallet-Mossop Process?
Initial Experiment
Additional Parameterizations
Conclusion
Motivation
• ICE is complicated:
diverse morphologies,
shapes and sizes
• Influences: radiation
feedback, cloud
formation, precipitation,
etc.
• Better understanding of
ice in atmosphere >better understanding of
dynamics of atmsphere
Ice Formation
• Ice formed via
▫ Homogeneous nucleation
 No nuclei present
 At temperatures <-34°C
▫ Heterogeneous nucleation
 Nuclei are present
 Best nuclei: size, in-soluble,
similar lattice structure
Heterogeneous nucleation of
supercooled liquid water
drops
http://youtu.be/O0uwGlgkgfY
Evidence for Ice Multiplication
Fletcher-Ice Nuclei Curve
𝑙𝑛𝑁 = 𝑎(𝑇1 − 𝑇)
Meyes –Ice Nuclei Curve
𝑁 = exp[𝑎 + 𝑏[100 ∗ (𝑆𝑖 -1)]]
Hobbs, V. P. (1968). Ice Multiplication in
Clouds. Journal of the Atmospheric
Sciences, 315-318.
• No one-to-one relation between ice nuclei and
ice particle concentration
• Must be secondary process for ice crystal
formation
• -Ice Multiplication
Hallet Mossop Process
Hallett, J., & Mossop, S. C. (1974, May 3).
Production of secondary ice particles
during the riming process. Nature, 249,
26-28.
Hallet Mossop Process
Hallet-Mossop Process
Parameterization
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Environmental Temperature range -3°C to -9°C
Droplets radius >20𝜇m
Rimer Temperature range -3°C to -9°C
Estimated 300 splinters ejected per cm^3 rime
accreated
Conclusions
• Hallet-Mossop process best candidate for Ice
Multiplication Mechanism
• More work to be done:
▫ Correlate with droplet size, fall speed, rimer size
▫ Develop theoretical explanation of mechanism
• Better understanding of process->better
understanding of microphysical properties of
clouds
Bibliography
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Supercooled Water Droplets. (2011, January 11). Retrieved May 8, 2011, from SkyLibary:
http://www.skybrary.aero/index.php/Supercooled_Water_Droplets
Barrel, J. A. (n.d.).
Choularton, T. W. (1978, August 24). A Possible Mechanism of Ice Splinter Production During Riming. Nature, 274, 791-792.
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