Stability and Cloud Formation Flashcards
What are the 3 key risks associated with cloud development?
Risk of icing
Risk of turbulence
Risk of precipitation
What are the 5 initial causes of an air parcels vertical motion?
Convection Turbulence in the friction layer Orographic lift Convergence Frontal lift
What is the ELR?
Environmental lapse rate, rate at which temperature changes with height
What is the ISA ELR?
-2 degrees per 1000ft/-6.5 degrees per 1km
How is the ELR measured?
Radiosonde
What is adiabatic cooling?
As a parcel of air rises it enters low pressure
The parcel of air will expand resulting in a loss of temperature
What is adiabatic warming?
When a parcel of air sinks it enters high pressure
The parcel of air compresses resulting in an increase in temperature
What is the DALR?
Dry Adiabatic Lapse Rate
-3 degrees per 1000ft/-1 degree per 100m
What happens when a parcel of air reaches 100% RH?
Condensation occurs, latent heat is released which effects the rate of cooling
What is the SALR?
Saturated Adiabatic Lapse Rate
-1.8 degrees per 1000ft/-0.6 degrees per 100m
Why is the SALR less than the DALR?
Due to latent heat released during condensation
When do you get an absolutely stable atmosphere?
When the DALR>SALR>ELR
Air does not rise buoyantly
What is the strength of turbulence in absolute stability?
Nil/light
What is the strength of icing in absolute stability?
Light to moderate rime ice
What is the visibility in absolute stability?
Poor
What is the strength of convection in absolute stability?
None
What type of clouds are found in absolute stability?
Stratus
Nimbostratus
Altostratus
When do you get absolute instability?
ELR>DALR>SALR
Air rises buoyantly
What kind of precipitation do you get in absolute instability?
Storms, showers, potential microburst, hail
What strength of turbulence do you get in absolute instability?
Moderate to severe
What is the visibility in absolute instability?
Good, reducing in showers
What is the strength of icing in absolute instability?
Severe clear ice, mixed ice and rime ice in higher cloud
What type of clouds are found in absolute instability?
Cumulus Towering cumulus (congestus) Cumulonimbus Stratocumulus Altocumulus
What is conditional instability?
DALR>ELR>SALR
Unsaturated air does not rise buoyantly
Saturated air rises buoyantly
What are the 4 causes of cloud dispersal?
- Warming through subsidence (adiabatic warming)
- Warming through absorbing solar or terrestrial radiation
- Reduced convective activity (reduced buoyancy)
- Mixing unsaturated air outside of cloud
