Chapter 5-Condensation Flashcards
What conditions are necessary for dew to form?
Dew forms when the temperature of objects cools below the dew point, typically on clear nights due to increased radiative cooling.
How does frost differ from frozen dew?
Frost forms when the temperature drops below the frost point, causing water vapor to deposit directly as ice crystals. Frozen dew occurs when liquid dew forms and later freezes as temperatures drop.
Where does dew or frost typically form first, and why?
Dew or frost forms first on surfaces that transpire moisture (twigs, grass) and surfaces that store little heat (like metal and windshields) because they cool faster.
What are the factors that control the formation of dew and frost?
-Clouds trap heat and limit cooling, reducing dew formation.
-Water vapor increases the dew point, enhancing dew/frost potential, but also limits heat loss.
-Winds mix warmer air from above, reducing the potential for dew/frost formation.
What is the difference between hoarfrost and black ice?
Hoarfrost forms delicate ice crystals through water vapor deposition, while black ice forms from frozen dew on roadways.
What are condensation nuclei (CN) and why are they important for condensation?
CN are particles suspended in the air upon which water vapor condenses, acting as surfaces that facilitate condensation, particularly for cloud droplet formation (CCN).
What is the difference between hygroscopic and hydrophobic CN?
Hygroscopic CN attract water even at RH < 100% (e.g., sea salt), while hydrophobic CN repel water unless RH > 100%.
What is the Kelvin effect and how does it relate to cloud droplets?
The Kelvin effect describes how smaller droplets (< 10 μm) require higher supersaturation to prevent evaporation due to their curved surfaces. This effect diminishes for larger droplets (> 20 μm).
What causes haze to form, and what is the difference between dry and wet haze?
Haze forms when small particles scatter sunlight. Dry haze scatters sunlight at low RH (Rayleigh scattering), while wet haze occurs at higher RH (>75%), with larger wet particles scattering light (Mie scattering).
What are the main types of fog and how do they form?
Radiation Fog: Forms by radiative cooling at the surface, often in valleys.
Advection Fog: Forms when warm, moist air moves over a cooler surface.
Upslope Fog: Forms when air cools as it rises along a slope.
Evaporation Fog: Forms from water evaporating into cooler air, includes steam and frontal fog.
Mixing Fog: Forms when unsaturated air parcels of different temperatures mix, leading to condensation.
How do radiation fog and advection fog differ?
Radiation fog forms by cooling at the surface on clear nights, while advection fog forms when warm, moist air passes over a cooler surface and cools to saturation.
What is the difference between mist and fog in terms of visibility?
Mist has higher visibility (0.8 km to 10 km), while fog has lower visibility (< 0.8 km).
What role do CCN (cloud condensation nuclei) play in cloud formation?
CCN provide surfaces for water vapor to condense, facilitating the formation of cloud droplets and helping overcome the “curvature effect” associated with small droplets.
What is the relationship between fog and clouds?
Fog is essentially a cloud that forms at the ground level when air cools to below its dew point, resulting in visible condensation near the surface.
What are the main factors used to classify clouds?
Clouds are classified by altitude (low, middle, high, or vertical development) and appearance (shape, density, color).
