Chapter 7 - Precipitation Flashcards
Would the collision-coalescence process work better at producing rain in (a) a warm, thick nimbostratus cloud or (b) a warm, towering cumulus congestus cloud? Explain.
a warm towering cumulus congestus cloud because rising air currents slow the rate at which droplets fall which will allow them to grow in size
When the temperature in a cloud is -30°C, are larger cloud droplets more likely to freeze than small cloud droplets?
Yes. Freezing of pure water (spontaneous/homogeneous) freezing occur when enough molecules within the water droplet join together in a rigid pattern to form a tiny ice structure (ice embryo). Larger droplets are theremore more likely to freeze.
How cold does it have to be for a cloud droplet of the size 25 µm to freeze spontaneously?
-40°C
How does the ice-crystal (Bergeron) process produce precipitation? What is the main premise describing this process?
If we suppose that the cloud droplet and ice crystal are saturated and in equilibrium. The saturation vapor pressure is greater over the water droplet than the ice crystal. This causes water vapor molecules to move from the water droplet to the ice crystal. This causes more water vapor to evaporate and move continuously to the ice crystal that grows in size.
List the advantages and disadvantages of heavy snowfall.
advatages: snow is a good insulator, protects crops, and the melting snow in spring and summer is of great economic value in that it supplies streams and reservoirs with much-needed water. disadvatages: avalanches, harder to drive on roads.
List and describe three ways in which ice crystals can form in a cloud.
- Vapor deposition(Diffusional growth) – The vapor pressure over an ice crystal is
much lower than that over a liquid droplet. - Accretion – As ice particles fall through the cloud at a higher velocity than cloud
droplets, it collides and collects the supercooled droplets, which freeze upon contact
with the crystal, producing graupel (snow pellets). - Aggregation – Ice crystals falling through the cloud can collide with each other and
stick together, producing snow flakes.
What atmospheric conditions are necessary for snow to fall when the air temperature is considerable above freezing?
The air must be unsaturated, and the wet-bulb temperature must be at freezing or below (the lowest temp. that can be attained by evaporating water in to the air).
Why is hail more common in summer than in winter?
There are more violent thunderstorms in summer. The hailstones grow large enough to reach the surface before melting.
Clouds that form over water are usually more efficient in producing precipitation than clouds that form over land. Why?
Precipitation occurs when the water droplets become too large and heavy and can no longer be supported by the atmosphere and fall out of the cloud. Over water there will be a more continuous supply of water to evaporate, and hence a build up of the droplets in the cloud occurs. This will cause more rain to happen.
