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21 Cards in this Set
- Front
- Back
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Define nucleation process
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The action leading to the formation of the first new specks during a change of state at the boundary between two phases
301.1.1 |
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Describe natural condensation as a nucleation process
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- does not require condensation nuclei
- does require extremely high supersaturations 301.1.1 |
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Describe heterogeneous condensation as a nucleation process
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- impurities acting as embryos
- hygroscopic impurities can become impregnated with water even without air saturation - non-hygroscopic impurities require air supersaturation 301.1.1 |
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Define hygroscopic impurities
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- water soluble
- examples are sea spray salt, combustion particles 301.1.1 |
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Name the 3 types of condensation nuclei as distinguished by their dimensions
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- Aitken nuclei, less than 1/10 micrometer
- large nuclei, 0.1 to 1 micrometer - giant nuclei, 1 micrometer or more 301.1.1 |
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State the impact of the 3 types of condensation nuclei as distinguished by their size
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Aitken nuclei:
- too small - negligible role even in great concentration Large nuclei: - most active nuclei - concentration varies from 10-1000/cm3 Giant nuclei: - negligible role because of small number 301.1.1 |
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Describe the growth rate by condensation of a droplet
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- fast then slow
- 1-10 micrometers: 1 sec - 10-100 micrometers: 6 min - 100-1000 micrometers: 3 hrs - 1-3 mm: days 301.1.1 |
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Describe supercooling
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- water in a liquid state when temp is less than 0C
- is the process of cooling water droplets beyond the nominal freezing point 301.1.1 |
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Describe homogeneous solidification as a nucleation process
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- does not require nuclei
- requires extremely high supersaturation or very low temps 301.1.1 |
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Describe heterogeneous solidification as a nucleation process
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- particles acting as freezing nuclei
- freezing nuclei have property of starting solidification process for supercooled droplets - mixture of hygroscopic and solid substance creates condensation, then freezing - natural freezing nuclei area much rarer than condensation nuclei - ice crystals/fragments act as nuclei for new or larger crystals 301.1.1 |
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List the 4 factors that control the evolution of clouds
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- water vapor
- condensation and ice nuclei - stability - lift 301.1.2 |
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Explain the effect that water vapor has on the evolution of clouds
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- warms saturated air holds more vapor than cold saturated air
- cooling warm saturated air condenses more moisture than cooling cold saturated air - at sea level, saturated mixing ration apprx doubles for every 10C gain in temp 301.1.3 |
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Define: Saturated mixing ratio
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Theoretical max amount of water vapor that air can hold at a specific temp and pressure
301.1.3 |
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Explain the effect that condensation and ice nuclei have on the evolution of clouds
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- size and concentration of nuclei determine size and concentration of droplets/ice crystals
- ratio of ice crystals to supercooled droplets increase as temp decreases - higher in cloud, the more ice crystals and the less supercooled droplets 301.1.3 |
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Explain the effect that stability has on the evolution of clouds
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- stability or instability of air determines whether formed cloud is stratiform or cumuliform
- stability measured via tephigram analysis, using data from radiosonde 301.1.3 |
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Explain the effect that lift has on the evolution of clouds
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- most clouds form when moist air subjected to upward motion and cools to saturation point, called Lifting Condensation Level or LCL
- lift types are convection, mechanical turbulence, orographic lifting, large scale lift 301.1.3 |
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List the 4 types of vertical motion that assist in the formation of clouds
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- large scale lift
- convective lift - orographic lift - mechanical turbulence 301.2.1 |
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Explain the mechanism of convective lift as it assists in the formation of clouds
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- requires unequal heating
- certain parcels of air gain buoyancy over the surrounding air - two main processes that initiate convection: daytime heating and cold air advection 301.2.2 |
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Explain the mechanism of mechanical turbulence as it assists in the formation of clouds
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- eddying motion of the air caused by friction
- intensity and height of effect depends on: roughness of surface, strength of wind, and instability of air - always be inversion on top of mixed layer - frequently SC 301.2.2 |
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Explain the mechanism of orographic lift as it assists in the formation of clouds
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- extent and rate of ascent of air depends on slope and height of terrain and strength of wind
- extent of cloud depends on air moisture - type of cloud depends on stability - little or no cloud if air is dry - stratiform cloud from moist, stable air - convective cloud from moist, unstable air 301.2.2 |
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Explain the mechanism of large scale lift as it assists in the formation of clouds
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- slow air mass ascent or descent caused by convergence or divergence
- large region of horizontal convergence in boundary layer coupled with large region of horizontal divergence in upper troposphere - at least several hundred km - convergence into areas of low pressure/troughs and result in upward moving air currents - divergence at surface with ridges/high pressure systems create downward motion - general rate of ascent very slow 301.2.2 |
