Stability and Instability Flashcards
What is a stable parcel of air vs an unstable one?
- An exampled of an unstable parcel of air would be a balloon filled with 20oC air rising up into colder air and then continuing to rise because it is warmer than the air surrounding it.
- An example of stable air would be a 20oC parcel of air rising but the air aloft is warmer, so the parcel can no longer rise and sinks back down to where it was.
- Unstable: air keeps rising and expanding
- Stable: air goes back to where it was
What is an adiabatic process?
A parcel of air that does not interact with the air around it. Very rare, but this is the best way to think of it
What kind of effects can you expect in stable air?
Stable air isn’t moving much or at all. This results in:
- Smooth flying
- Poor visibility
- Steady precip
- Layer cloud
- Fog
- Shallow environmental lapse rate
- Inversion
- Warm air moving over cold air
How does air become more stable?
- Surface cooling (radiation at night/advection). If the parcel of air at the surface is already cold, it wont me able to rise into the even colder, denser air above it. This makes the atmosphere more stable.
- Warming at high altitude. If warm air moves above colder air it will have the same result as above. Colder air below will not be able to rise even tho it itself was not warmed. This makes the atmosphere more stable.
What is subsidence inversions?
An area of descending air that warms as it descends due to the increase in atmospheric pressure (compression) at lower altitudes.
The sinking air rarely goes right to the ground and instead hangs around in a layer that is warmer than the air below it.
Exampple: Was common in YYC in the winter. -30 on the ground and close to 0 a few thousand feet up.
What are the characteristics of unstable air?
- Bumpy flying
- Good visibility
- Showry precip
- Cumulus cloud
- Ultimately - Thurnderstorms
- Steep lapse rate
- High temp/dew point spread
What are the characteristics of unstable air?
- Bumpy flying
- Good visibility
- Showry precip
- Cumulus cloud
- Ultimately - Thurnderstorms
- Steep lapse rate
- High temp/dew point spread
How do we create unstable air?
Warmer air aloft creates a stable atmosphere by making sure colder, denser air cannot rise and cause problems.
So colder air aloft is the key to an unstable atmosphere. This lets air rise and rise and mix and tumble etc etc
What are the four types of lapse rates?
- Steep (unstable air)
- Shallow (conditionally unstable air)
- Inversion (air is stable)
- Isothermal layer (air is stable)
An environtmental lapse rate that is ____ than the DALR or the SALR will produce very _____ air.
- less
- stable
What are ways to cause surface heating an therefore instability.
- Radiation
- Conduction
- Advection
- convection
What is absolute and conditional stability?
- Absolute Stability: A parcel of rising air, or air that is trying to rise, would always be cooler than the air surrounding it. Another way of saying this is the DALR and SALR are steeper than the ELR. So colder air has nothing to ‘grab on to’ to climb through the warmer air because it is denser. This is true whether the air is saturated or not.
- Conditional Stability: Stability depends on whether the air is saturated or not when it started to rise. We could also say that the DALR is steeper than the ELR but that the ELR is steeper than the SALR.
What is absolute and potential instability?
- Absolute Instability: The ELR is steeper than both the SALR and DALR. The parcelt of air, once started, will just rise and rise.
- Potential Instability: Depends on some kind of trigger such as lift. Mirrors conditional stability
What is subsidence?
Subsidence is when air sinks, which results in compression, which results in the air being warmed.
