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Motivated by the need to understand the microphysics and improve the remote sensing of the melting layer of precipitation, we have developed a numerical 3-D model for the melting of single snowflakes. The model uses the smoothed particle hydrodynamics method and is forced by surface tension that controls the flow of meltwater on the ice surface. Heat transfer from the environment to the snowflake is simulated with a Monte Carlo scheme. In model experiments with snowflakes of various sizes and densities, we observed that the meltwater tends to initially gather in concave regions of the snowflake surface. These liquid water regions merge as they grow, and as meltwater is added, they form a shell of liquid around an ice core. This eventually develops into a water drop. The observed features during melting are consistent with experimental findings from earlier research, which suggests that the model is adequate for exploring the physics of snowflake melting. The principal remaining uncertainties arise from the omission of aerodynamic forces from the model. The results suggest that the degree of riming has a significant influence on the melting process: During initial melting, liquid water is apparent on the surface of unrimed or lightly rimed particles, while rime provides a porous structure that can absorb a relatively large amount of meltwater. Riming also strengthens the connections between different parts of the snowflake, making rimed snowflakes less prone to breakup during melting, while unrimed ones break up rather easily.

Plain Language Summary Rain often starts as snow higher in the atmosphere, where it is colder. The snowflakes melt as they fall into above-freezing temperatures. The layer of melting snowflakes can, among other things, affect weather patterns, block radio signals, and be a hazard to aircraft. Our study was the first to simulate the melting of snowflakes in 3-D by reproducing the physical processes involved on a computer. The behavior of meltwater on the simulated snowflakes is very similar to that seen in observations of real ones. The simulation can help us better understand the details of the melting process and how the snowflake type affects it, as well as create better models for the interaction of melting snowflakes with radar and telecommunication signals.