Crystals grow faster in warmer temperatures due to the liquid containing the dissolved material evaporating quickly. This is because the competitive nucleation of bcc and fcc crystals from non-equilibrium liquids is studied by simulating phase field crystals. Diffusion-controlled anisotropic growth of stable and metastable crystalline polymorphs in the phase-field crystal model is also observed. Deposition can produce crystals with a cloud size of around 1 mm, but it is generally not large enough to cause much precipitation on the surface. The habit or crystalline form of a growing ice crystal is determined by the temperature and the associated saturation vapor pressure difference between ice and supercooled water.
We can observe rapid wall-assisted crystallization until the growth front meets the small crystal nucleus caused by spinodal nucleation within the sample. At these temperatures, ice crystals grow at the expense of water droplets, as water vapor molecules migrate to crystals. In addition, we can see that the intrinsic mechanical instability of a disordered vitreous state attached to the crystal growth front allows rapid growth of domino-like crystals even at ultra-low temperatures. The crystals then fall through a molten (warm) layer that is deep or warm enough to completely melt the crystals into droplets of water. The liquid molecules on the outer surface of crystals serve to increase the bond between two colliding crystals.
Depending on temperatures and cloud saturation levels, ice crystals can grow in a variety of crystalline shapes or habits. For ice crystals to form in clouds, the water molecules that form the vaporous droplets of clouds need a substrate on which to begin the formation of a crystalline network of ice. At temperatures above -10 °C, there are not enough deposition nuclei present to form sufficient crystals for an efficient precipitation process to occur, although crystals can still form.
