ESCI 2410 Stability

A comprehensive overview of the concepts related to stability in atmospheric science.

What defines stable equilibrium in atmospheric terms?

A state where, when pushed from its resting place, it returns to its starting position.

What happens in unstable equilibrium?

When pushed from its resting place, it continues to move further away from its starting position.

What is a parcel of air?

A small volume of air that does not mix with the surrounding air and can expand, contract, and move but cannot exchange mass or energy.

What characterizes an adiabatic process?

A process in which no energy is gained or lost to the surroundings.

What is the dry adiabatic lapse rate?

The rate at which a dry parcel of air cools with height.

What distinguishes moist adiabatic lapse rate from dry adiabatic lapse rate?

Moist adiabatic lapse rate refers to the rate at which a saturated parcel of air cools with height.

What is the environmental lapse rate?

The observed temperature change with height, typically about 10°C/km or 5.5°F/1000ft.

How does pressure change with height according to thermodynamics?

Pressure decreases with height, plotted logarithmically.

What do the lines on a thermodynamics chart represent?

Black lines represent constant temperature, red lines indicate dry adiabats, blue lines indicate moist adiabats, and green lines indicate mixing ratios.

What indicates absolute stability?

The environmental lapse rate is less than the dry and moist lapse rates, causing lifted parcels to be cooler than the environment.

What occurs in stable air conditions?

Conditions where surface air is cooling, often related to high pressure systems and subsidence inversions.

What defines absolute instability?

The environmental lapse rate is greater than the dry lapse rate, resulting in lifted parcels becoming warmer and continuing to rise.

What conditions define conditional stability?

When the environmental lapse rate is greater than the wet lapse rate but less than the dry lapse rate, dependent on air saturation.

What is convective instability?

Lifting a layer of air that is wet at the bottom and dry at the top, causing instability.

What is the effect of non-uniform heating in convection process?

It allows thermals to break free from the surface, rising as they mix with surrounding air.

What is the lifting condensation level (LCL)?

The level at which rising air meets its dew point, following mixing ratio lines.

What happens to air pushed over a mountain?

It forms a cloud at the LCL, resulting in upslope precipitation.

What occurs to air on the leeward side of a mountain?

It becomes drier and warmer than the air on the windward side due to sinking.