Part 2 — Cloud Formation, Lapse Rates & Stability

What is a contrail?

A visible trail of ice crystals formed from aircraft exhaust moisture in cold air.

What does the absence of a contrail suggest?

The surrounding air is generally too dry for a persistent visible contrail.

What four lifting mechanisms are emphasized in the review?

Orographic lifting, frontal lifting, convective lifting, and convergence lifting.

What is convergence lifting?

Air flows together horizontally near the surface and is forced upward.

What is convective lifting?

Uneven surface heating makes warm, buoyant air rise.

What is frontal lifting?

Air is forced upward when a front pushes one air mass over another.

What is orographic lifting?

Air is forced upward when it encounters a mountain or elevated terrain.

Which lifting mechanism involves mountains?

Orographic lifting.

Which lifting mechanism involves surface heating?

Convective lifting.

Which lifting mechanism involves colliding airflows?

Convergence lifting.

Which lifting mechanism involves fronts?

Frontal lifting.

What is the dry adiabatic lapse rate?

Approximately 10°C/km; the cooling rate of rising unsaturated air.

What is the saturated adiabatic lapse rate?

Approximately 6°C/km; the cooling rate of rising saturated air.

What is the typical environmental lapse rate?

Approximately 6.5°C/km; the actual atmospheric temperature decrease with height.

Why does rising unsaturated air cool?

Pressure decreases with altitude, so the parcel expands and cools adiabatically.

Why does saturated air cool more slowly than dry air?

Condensation releases latent heat, partially offsetting expansion cooling.

Which is greater: dry or saturated adiabatic lapse rate?

Dry: about 10°C/km; saturated: about 6°C/km.

What happens to a dry air parcel's temperature as it rises?

It decreases by approximately 10°C for every kilometer of ascent.

What happens to a saturated parcel's temperature as it rises?

It decreases by approximately 6°C for every kilometer of ascent.

What is atmospheric stability?

The atmosphere's tendency to resist or encourage vertical air-parcel movement.