Diamond dust
Small falling ice crystals which are made by ※1sublimation of water vapor in the atmosphere are called diamond dust. The phenomenon of these crystals being hit by sun light and shining is called this ,too. You can watch diamond dust when it is sunny from downing to morning,there is no wind, temperatures are below -10 ℃ and visibility is more than 1km. Unlike diamond dust, ice crystals that float in the atmosphere are called ice fog. You can watch ice fog in a place where the atmosphere is stable and when temperatures are below -30 ℃ and visibility is less than 1km.
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※１ sublimation・・・The phenomenon of an element or compound changing to a solid from a gas, or changing to a gas from a solid.Here,I discuss the former.