Droplet accretion during rime growth and the formation of secondary ice crystals

Advances in Laboratory Cloud Physics 1987–1990

“…This result casts doubt on the validity of a critical supersaturation concept for defining nucleation scavenging of such particles. The supersaturation dependence of CCN/CN ratios were in agreement with Hallett et al [1989] for soot produced from burning acetylene: 0.46 at 1.3% and 0.93 at 2.1%.…”

“…Carbonaceous aerosols which form in combustion processes can be active in cloud processes and can have effects over a wide range of processes, such as the formation of cirrus cloud particles, radiative properties of clouds, the global radiation balance, and anthropogenic effects on scales from local to global. Hallett et al [1989] and Rogers et al [1990] studied the condensation nuclei (CN) and CCN properties of carbonaceous aerosols produced by burning acetylene, jet fuel, or wood in oxygen‐rich or oxygen‐poor flames. Measurement of CN and CCN (1% supersaturation) were made with continuous flow counters.…”

“…Dong and Hallett [1988; 1989] performed experiments to evaluate the shell shatter theory, where individual drops rime onto an ice target. Using microphotographs of rime grown in a temperature controlled horizontal wind tunnel, they determined that accreted droplets spread during freezing in the −3 to −8°C regime of the “Hallett‐Mossop” mechanism.…”

The Geometry of Rimed Aggregate Snowflakes: A Modeling Study

“…The lowest densities occur for low temperatures around −20 °C and low impact velocities typical for the collisions between snowflakes and cloud droplets ( v i ≤ 1 m/s). Although the LDR simulations give rise to a random loose packing of rime with a very low density, the so‐called feather rime , as it is observed at very cold conditions below −20°C, can have even lower densities around 150 kg/m 3 (Dong & Hallett, ; Macklin, ; Williams & Zhang, ). That rime is not necessarily a solid mass is also shown by the electron microscopy images of Rango et al (), which clearly show an open network of branches within the rime structures (their Figures 17, 19, and 20).…”

Research in Cloud and Precipitation Physics: Review of U. S. Theoretical and Observational Studies, 1987–1990

“…However, the mechanism behind the Hallett‐Mossop process remains controversial. Dong and Hallett [1989] argued that the Griggs and Choularton [1983, 1986a,b] model of splinter ejection following freezing of a shell around accreted droplets was not consistent with their new laboratory observations. They proposed a new mechanism in which thermal stress in the accreting drop causes it to fracture when part is frozen near 0° C and then cools to the substrate temperature.…”