ATMOSPHERIC  STABILITY

 The key to atmospheric stability is the environmental lapse rate (ELR), the rate at which the
 temperature drops with increasing altitude.  The more rapid the temperature drop with
 increasing altitude, the greater the degree of instability.  The ELR is quite variable.

ELR value
 (listed in order of
increasing stability)

Atmospheric State

Comments

ELR > DAR > MAR

Absolute Instability

All parcels are unstable.  This is an unusual condition except in thin layers near the surface.

DAR > ELR > MAR

Conditional instability

Dry parcels are stable, moist parcels are unstable. The degree of instability is variable.  The closer the ELR is to the DAR, the more unstable is the atmosphere.

DAR > MAR > ELR > 0

Absolute stability, no inversion

Both dry and moist parcels are stable.  The smaller the ELR, the greater the stability.

DAR > MAR > 0 > ELR

Absolute stability,  inversion

Inverted layers are extremely stable, e.g., the stratosphere

Dry adiabatic rate º DAR » 10°C/km » 5.5°F/1000 ft (nearly constant in value).

Moist adiabatic rate º MAR » 6°C/km » 3.3°F/1000 ft (decreases with increasing T).

Standard (~average) environmental lapse rate º ELRSTANDARD » 6.5°C/km » 3.6°F/1000 ft.
(The actual ELR is highly variable with time and layer.)

The dew point lapse rate º DPLR » 2°C/km » 1°F/1000 ft