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单词 precipitation
释义
precipitation

Physics
  • Any of the particles of water that fall from the atmosphere and reach the ground, e.g. rain and snow. Rain is an example of liquid precipitation, while snow is an example of solid precipitation. Precipitation is distinguished from other forms of hydrometeor, such as dew, fog, and hoarfrost, since they do not involve the water particles falling to the ground.


Chemistry
  • 1. All liquid and solid forms of water that are deposited from the atmosphere; it includes rain, drizzle, snow, hail, dew, and hoar frost.

    2. The formation of a precipitate.


Chemical Engineering
  • The formation of a suspension of solid particles, known as a precipitate, as the result of a chemical reaction or a physical change such as through the reduction in the solubility of the dissolved material in the solvent. Solid materials can be formed in a solution by the addition of compound, which causes a reaction in the solution that converts the material to be separated into an insoluble state. The solid material can then be separated by centrifugation or filtration. Liquid materials can also be precipitated as a condensate from a gas. Precipitation is used to separate metals from aqueous solutions, and also be used to separate impurities and contaminants from biochemical processes. A precipitator is a vessel used to carry out the process of precipitation.


Geology and Earth Sciences
  • 1. In meteorology, all the forms in which water (H2O) falls to the ground as rain, sleet, snow, hail, drizzle, or other more specialized forms, and also the amounts measured. Sometimes precipitation seen falling from clouds evaporates before reaching the ground. The term also includes dew, frost, clear ice, fog, and other forms in which atmospheric moisture is precipitated as water but without falling from clouds.

    2. The process of depositing dust or other substances (pollution) from the air.

    3. The deposition of solid particles out of a supersaturated solution.


Geography
  • In meteorology, the deposition of moisture from the atmosphere onto the Earth’s surface in the form of rain, hail, frost, fog, sleet, or snow. Initially, cloud droplets grow around nuclei through condensation and diffusion. In warmer clouds the larger droplets then grow by collision and coalescence with the smaller ones. In colder clouds the Bergeron–Findeisen mechanism is thought to operate, probably in conjunction with the growth of ice crystals: through accretion, as supercooled water droplets freeze on impact with the ice; and aggregation, as smaller ice crystals stick to larger ones. Much precipitation begins in the form of ice crystals, but melts as it falls, to become rain. Variations in the intensity, amount, timing, duration, and frequency of precipitation, whether frozen or liquid, have important implications on the physical, chemical, and biological processes on Earth. See Zhang et al. (2007) Nature 448 on anthropogenic precipitation; Holmer (2007) Geograf. Annal. 89, 4 on rainfall change; Halfon and Kutiel (2007) Eur. Geosci. Union 9 on precipitation mapping; and Malby et al. (2007) Hydrol. Scis J. 52, 2 on long-term variations in orographic rainfall.


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