Hallet-Mossop Process as a Mechanism for Ice MultiplicationSteven BrownAtmospheric Sciences 5/16/2011

Outline•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 dropshttp://youtu.be/O0uwGlgkgfY

Evidence for Ice Multiplication

-1)]]

𝑙𝑛𝑁=𝑎(𝑇1−𝑇 )Fletcher-Ice Nuclei Curve

Meyes –Ice Nuclei Curve

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•Environmental Temperature range -3°C to

-9°C•Droplets radius >20m•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

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