Atmospheric Stability Flashcards
What happens to a parcel of air as its temperature increases?
As temperature increases its density will decrease, and it surronded by colder, denser air, the warmer parcel of air will tend to rise.
What does adiabatic mean?
A process in which heat energy does not enter or leave a system, but the temperature may change.
How does the adiabatic process work in the atmosphere?
Pressure decreases with height, thus any air rising will expand and cool adiabatically while descending air will be heated adiabatically by compression.
During such changes in temperature, no heat energy is exchanged because air is a poor conductor.
What is a change of temperature with height known as?
Lapse Rate
What are three significant lapse rates?
Dry Adiabatic Lapse Rate (DALR)
Saturated Adiabatic Lapse Rate (SALR)
Environmental Adiabatic Lapse Rate (ELR)
What is the Dry Adiabatic Lapse Rate (DALR)?
When unsaturated air rises, it cools at a constant rate due to the adiabatic process. This rate is referred to as the DALR and its value is 3°/1000ft
When air sinks, it is compressed and the process is reversed, so unsaturated air is warmed at the DALR, 3°/1000ft.
What is the Saturated Adiabatic Lapse Rate (SALR)?
When rising air is cooling, it will eventually become saturated.
Further lifting and cooling will result in condensation. Condensation releases heat, warming the air and reducing the rate at which it cools. While condensation takes place in a parcel of rising air, it cools at the SALR.
SALR is typically 1.5° to 2°/1000ft.
It is not constant and depends on the amount of water and pressure in the air. SALR is lower when the humidity and pressure are high and it generally increases slightly with altitude.
What is the Environmental Adiabatic Lapse Rate (ELR)?
The rate at which air cools with altitude at any given time and location is the ELR. The ELR is normally less than the DALR, but can take almost any value. It can even exhibit a temperature increase with height, known as a temperature inversion.
Define atmospheric stability in laymens terms
Air is said to be unstable if it rises and stable if it does not. Sinking air is stable.
Why does air rise?
Whether or not air rises depends upon its temperature in comparison with the surrounding air.
What is the average lapse rate?
1.98°/1000ft
If the ELR is less than both the SALR and DALR, what is the layer described as?
Absolutely unstable
If the ELR is less than the SALR but more than the DALR, what is the layer described as?
Conditionally stable
If the ELR is less than both the SALR and the DALR, what is the layer described as?
Absolutely unstable
What value is the SALR?
1.5°/1000ft
