Summary of the article on snow aging:

Snow Aging and Effective Grain Size

- Snow aging is represented by the evolution of the ice effective grain size (re), which is related to the specific surface area (SSA) of the snow.
- Dry snow metamorphism and liquid water-induced metamorphism drive changes in the effective grain size over time.
- The net change in effective grain size each time step is calculated as a sum of changes due to dry snow metamorphism, liquid water-induced metamorphism, refreezing of liquid water, and addition of freshly-fallen snow.
- Dry snow aging is based on a microphysical model that simulates diffusive vapor flux among ice crystals, with parameters retrieved from a lookup table based on snow temperature, temperature gradient, and density.
- Liquid water-induced metamorphism is represented using a parametric equation that depends on the mass liquid water fraction.
- When snow layers are combined or divided, the effective grain size is calculated as a mass-weighted mean of the two layers.
- The allowable range of effective grain size is 30-1500 μm, corresponding to the range over which Mie optical properties have been defined.