Stability

What is an adiabatic process?

- A closed system

- Air changes temperature but not state

- No energy lost or gained to/from surrounding environment

What is the DALR?

3°C/1000ft

What is the SALR?

1.5°C/1000ft

What is the average ELR?

2°C/1000ft

What is difference between the DALR and SALR?

DALR is the rate at which dry air cools and SALR is the rate at which saturated air cools

Why is SALR lower than DALR?

As parcel rises and cools, water vapour condenses (can't hold as much moisture), it releases energy, reducing rate of cooling

Why is the SALR not constant with altitude?

It will eventually match the DALR as the atmosphere dries out with height, moisture is condensed and precipitated out

What is atmospheric stability?

- How a volume of air behaves after it's been disturbed (vertically)

- Compares temperature of vertically moving parcel with surrounding atmosphere

How does atmospheric stability affect average meteorological conditions?

- Unstable, will keep moving when disturbed, rain, turbulence and cumuliform

- Stable, doesn't want to keep moving, stratiform

When is there absolute stability?

- ELR < SALR

- Both cool faster than surrounding atmosphere

When is there absolute instability?

- ELR > DALR

- Environment cools faster than all air parcels

What is conditional stability?

- DALR > ELR > SALR

- Dry air stable but saturated is unstable

What is convective stability?

- Lower layer is dry

- Upper layer is wet

What is convective instability?

- Lower layer is wet

- Upper layer is dry

What is diurnal stability and instability?

- ELR changing over time

- Short term variations in stability in friction layer

- From gradual warming/cooling of atmosphere

- Unstable early mornings

- Stable evenings

What can surface temperature and dew point show?

Relative humidity and saturation level

What do cloud types indicate?

Unstable vs stable atmosphere

What does comparing freezing level and surface temperature show?

Approximate ELR

What is saturation?

- 100% RH

- Holds max amount of water vapour possible at a given temperature

- Rate of condensation = rate of evaporation

What is vapour pressure?

Actual contribution of water vapour to pressure in a given volume

What is saturation vapour pressure (SVP)?

Max potential contribution of water vapour to pressure in a volume at a temperature if the volume was saturated

How does temperature change saturation and SVP?

- Affects ability of air to become saturated

- Higher temperature, harder to saturate and increases SVP