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Chapter07a - Precipitation I RECAP Moisturein theair(diffe...

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Precipitation I
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RECAP Moisture in the air (different types of humidity). Condensation and evaporation in the air (dew point). Stability of theatmosphere: determines thetypeof clouds Cloud formation: moist air rises up in theatmospherewhereit expands adiabatically, cools down, saturates and forms clouds. Chapter 7: precipitation. Any form of water (liquid or solid) that falls from a cloud and reaches theground.
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From droplets to raindrops Typical sizes (diameter) Condensation nuclei: 0.2 μ m Cloud droplet: 20 μ m Raindrop: 2000 μ m The cloud droplets need to grow in order to become raindrops! Growth is determined by the balance of condensation (C) and evaporation (E) C>E the droplet grows C<E the droplet gets smaller C=E the droplet stays thesame (in equilibrium), hence: Saturation (equilibrium) vapor pressure
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The growth of cloud droplets Curvature effect: Thesaturation water vapor pressuredepends on the curvature of thewater surface. The larger thecurvaturetheeasier it is for thewater molecules to leave the surface of theliquid water. The saturation vapor pressure for small droplets is higher thereforethey require morevapor to keep their size Bottom line: thesmaller thedroplet, the more difficult it is to grow. Small droplets don’t makeit as raindrops.
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