Cloud Formation & Cloud Types
It's all about water and altitude
Cloud formation
A cloud is born
To understand how clouds form remember this...
1) when air is compressed it heats up
2) when air expands it cools
3) as air rises, it will expand due to decreased air pressure SO air cools as it rises
4) when air reaches its dew point, it is saturated with water and condensation occurs
5) when rising air reaches its dew point a cloud will form
- adiabatic temperature changes: a temperature change that happens even though heat isn't added or taken away, but happen because air either expands or is compressed
- dry adiabatic rate: rate at which unsaturated air heats or cools as its altitude changes; air will cool 10 degrees Celsius for every 1000m it goes up, and will heat 10 degrees Celsius for every 1000m it descends
- wet adiabatic rate: rate at which saturated air heats or cools as its altitude changes; this rate is generally between 5 and 9 degrees Celsius for every 1000m the air changes in height
Getting air to rise
1) orographic lifting: occurs when air hits elevated terrains (such as mountains) and is forced upwards
2) frontal wedging: occurs when warm and cold fronts collide; the warmer air is forced up over the colder, denser air
3) convergence: occurs when lower level air flows together and is pushed upwards
4) localized convective lifting: occurs when there is unequal heating of the Earth's surface, such as the difference between a parking lot and the wooded park beside it
Stable vs Unstable
- occurs when there is a gradual decrease in air temperature as altitude increases
- a temperature inversion occurs when air temperature increases as altitude increases, this creates the most stable air
Unstable air tends to rise = clouds
- occurs when air is warmer (less dense) than the surrounding air
- the warm air will continue to rise until its temperature matches the air around it
How does this impact the weather?
- relatively thin, widespread clouds are formed
- light to moderate precipitation if any
- dreary, overcast day with light rain = stable air rising
When unstable air rises...
- thick, towering clouds
- potentially heavy precipitation, thunderstorms, possible tornadoes
- bubbly, cauliflower-shaped clouds = unstable air rising
Knowledge Check
Types of Clouds
Clouds are classified based on their form and height...
1) cirrus - high, white, thin clouds with a veil-like or feather-like appearance
2) cumulus - rounded, cauliflower shaped, individual clouds usually with a flat base
3) stratus - sheets or layers of clouds that cover most if not all of the sky
- all clouds reflect one of these three forms or are combinations or modifications of them
There are three levels of cloud heights
1) high: cloud bases are above 6000m
- cirrus, cirrostratus and cirrocumulus clouds are found at this level; these cloud types are not precipitation producers
2) middle: cloud bases are often 2000m to 6000m
- altocumulus and altostratus clouds are found at this level; these cloud types may produce infrequent, light precipitation
3) low: cloud bases are below 2000m
- stratus, stratocumulus and nimbostratus clouds are found at this level; these cloud types may produce light precipitation, however, nimbostratus clouds are one of the main rain producers
- fog occurs when the base of a cloud is on or very near the ground; can be caused by cooling air or by evaporation