Precipitation Flashcards
Relative Humidity
Relates the amount of water vapour in the air to the maximum that could be held in the air at the current temperature
Can more water vapour exist in warm or cold air?
Warm air - as the air temperature increases, more water vapour can exist and the ratio of the amount of water vapour in the air relative to saturation decreases
terminal velocity
the constant velocity which depends on size
what is the average raindrop size vs average cloud droplet size vs average condensation nucleus size?
2mm
0.02mm
0.0002mm
water droplets are attracted to _____ as adiabatic cooling occurs
condensation nuclei (CN)
How do you classify a warm cloud?
temperatures above 0 degrees C throughout the cloud
what is the most important mechanism for cloud droplet formation in warm clouds?
Collision-coalescence process
what happens uf a collector drop becomes larger than the drops around it?
The collector drop will become larger, compressing the air beneath it and pushes smaller droplet out of its path, preventing it from becoming lager and collision efficiency will be low.
Coalescence
When a collector drop and a smaller drop collide to create a larger droplet
coalescence efficiency
the percentage of colliding droplets that join together - often near 100%
Cool cloud classification
0 to -4 degrees C, but do can contain supercooled water that can exist up to -40C if no CN are present
Saturated Vapour Pressure (SVP)
the amount of pressure in the air needed to keep the amount of water in equillibrium at that temperature
Bergeron ice crystal process
- based on SVP of ice being lower than the SVP of supercooled water at the same temperature
- more difficult for water vapour to leave an ice surface than a liquid surface
- results in more deposition onto the ice crystal than there is sublimation from it
- rather bind to a snow flake or ice than water droplet
Accretion
Occurs when supercooled water droplets collide and coalesce with ice crystals
Aggregation
Occurs when 2 ice crystals join to form a larger ice crystal - more effective at milder temperatures
how does snow form
results from the growth of ice crystals through deposition, accretion, and aggregation
what are the different snow flakes
- stellar dendrites: most common
- sectored plates: very flat (plate-like) and fill spaced between compared to dentrites
- hollow columns:
- Needles:
- Spatial dentrites:
- Capped columns: same as hollow columns that melt, enter a new moisture zone and get capped
- Rimed crystals
- Irregulars
How many types of snowflake families are there?
6
What is the lake effect snow?
cold air moves over a warmer body of water, as the cold air passes over, it picks up heat and moisture.
the warm, moist air rises and cools, leading to cloud formation
The clouds move over the downwind shores, where it snows
episodic precipitation from rapidly developing cumuliform clouds are called ___?
Showers - can occur as rain or snow showers
cumuliform clouds
- how do they form?
- how do the droplets come down?
- have vertical development
- form as a result of convection, which is more vigorous during warmer months
- larger droplets fall first, then smaller ones as higher terminal velocity and less chance to evaporate
Are raindrops spherical or round?
initially spherical but flatten out on the bottom as they fall
as they flatten, the greater surface area on the bottom causes greater resistance and further flattening, evnentually breaking apart
Graupel
occurs when an ice crystal takes on additional mass by accretion and contains very small air bubbles that give it a spongy texture and milky white appearance
- graupel can remain in a cloud and act as condensation nuclei (CN) for hail formation
what type of process are thunderheads?
convenctive - large thermal expansions of air masses with a high relative humidity
