User:PaulMcGlynn/sandbox

Ice particle growth can best be modeled through an electrostatic analogy. Much like the rate of transport of charge is related to gradients in the electric field, the rate of transport of vapor is related to gradients in the vapor field surrounding the particle. Larger (smaller) gradients in the vapor field correspond to stronger (weaker) flow. From this analogy one can associate the particle to a certain ‘capacitance’ with respect to water vapor. This capacitance controls the rate at which vapor is modeled to deposit onto the surface of the particle. Where the vapor is deposited on the particle is dependent on the energy of the surface which is regulated by temperature and the local gradients in vapor field. The particle grows as a hexagonal prism due to the lattice structure of water molecules in ice, therefore vapor is incorporated onto the two basal or six prism faces. If vapor is deposited preferential to a basal face, the particle grows as a column or ‘needle’. If vapor is deposited preferential to the prism face, the particle grows as a plate. These two different shapes are known as primary habits. Due to the complexity of these shapes, the capacitance models the particle primary habit as an Oblate or Prolate spheroid. Where columns correspond to prolate spheroids and plates correspond to oblate spheroids. Columns grow in temperatures ranging from -5 to -10 °C and plates grow in temperatures ranging 0 to -5 °C and -10 to -40°C. At -10°C vapor is deposited roughly equally across basal and prism faces. A secondary habit can also develop depending on cloud supersaturation. Greater supersaturation tends to create more complex shapes such as dendrites.