stability and cooling/heating

How is the troposphere heated

The troposphere is heated from the Earth by terrestrial radiation and conduction.

What is terrestrial radiation

The Earth absorbs the sun’s rays, heats up, and emits its own radiation.

Which gases absorb terrestrial radiation

CO₂ and H₂O vapour.

Does terrestrial heating increase or decrease with altitude

It decreases as radiation energy lessens.

Which heats faster: land or water

Land heats quicker.

Which cools faster: land or water

Land cools quicker.

What is conduction

Heat transfer through direct contact.

How does conduction heat the air

Air in contact with the surface heats or cools depending on the surface temperature.

How deep into the troposphere does conduction affect

The first 4000 feet.

How is heat distributed vertically through the troposphere

By convection, turbulent mixing, release of latent heat, compression, and advection.

What is convection

Air warmed by radiation or conduction becomes less dense and rises.

What causes air to stop rising in convection

When it cools, becomes denser, and sinks.

Does convection occur on small scales, large scales, or both

Both.

What is turbulent mixing

Wind blowing over rough terrain produces eddies that mix air vertically.

What is an eddy

A circular motion of air moving contrary to the main flow.

What causes latent heat release

Condensation occurring after water vapour reaches its dewpoint.

What does evaporation require

Heat absorption.

What does condensation release

Latent heat into the atmosphere.

How is heat transported upward by latent heat

Water vapour carries heat aloft before releasing it during condensation.

What is compression in the atmosphere

Subsiding air enters higher pressure and warms as it compresses.

What is subsidence

Descending air from higher altitudes.

Why does compressional heating occur

Same amount of air molecules in less space increases temperature.

What is advection

Horizontal transport of atmospheric properties such as air and moisture.

When does advectional warming occur

When cool air moves over a warmer surface.

How is the atmosphere cooled

Temperature decreases with height; nighttime radiational cooling; conduction cooling the lower 4000 feet.

What is the Environmental Lapse Rate (ELR)

The actual temperature decrease with altitude at a given time and place.

What is the average ELR

1.98°C per 1000 feet.

Why does the atmosphere cool at night

More radiation is emitted than absorbed.

What is expansional cooling

As air rises, pressure drops, air expands, and temperature decreases.

Why does rising air expand

Air pressure decreases with altitude.

Define adiabatic. Occurring without gain or loss of heat.

What happens to a gas compressed adiabatically

Its pressure and temperature increase without heat exchange.

What happens to a gas expanded adiabatically

Its pressure and temperature decrease without heat exchange.

What is adiabatic heating

Heating due to compression of descending air.

What is adiabatic cooling

Cooling due to expansion of rising air.

What is the Dry Adiabatic Lapse Rate (DALR)

3°C per 1000 feet.

When does air cool at the DALR

When it is unsaturated.

What happens when rising air reaches dewpoint

Condensation begins.

What effect does condensation have on temperature

Releases latent heat, reducing the rate of cooling.

What is the Saturated Adiabatic Lapse Rate (SALR)

1.5°C per 1000 feet.

Why is SALR lower than DALR

Latent heat released during condensation warms the air.

Name the six adiabatic cooling methods. Orographic lift, upslope lift, frontal lift, mechanical turbulence, convection, convergence.

What is orographic lift

Air forced upward over a mountain.

What is upslope lift

Air cools as it is lifted up gradually rising terrain.

What is frontal lift

Warm air being forced upward along a front.

How does warm air rise along a warm front

It slides up over retreating cold air.

How does warm air rise along a cold front

Cold advancing air undercuts warm air, forcing it upward.

How does mechanical turbulence cause cooling

Air is pushed upward by surface friction and expands/cools.

Why does convection cause cooling

Warmer surface areas cause buoyant rising air that expands/cools.

What is convergence

Surface winds flowing inward toward a low pressure center and rising.

What is stability

The tendency of an object to return to its original position if displaced.

What is stable air

Air that resists vertical motion.

What is unstable air

Air that promotes vertical motion.

What is neutral air

Air that neither resists nor promotes vertical motion.

What determines whether air rises or sinks

Its buoyancy compared to the surrounding air.

When is air more buoyant

When it is warmer (less dense) than the surrounding air.

When does unstable air stop rising

When it becomes the same temperature as surrounding air.

How do you determine atmospheric stability

Compare the lapse rate of rising air to the lapse rate of surrounding air.

What is the surrounding (non-rising) air lapse rate

2°C per 1000 feet (ICAO standard lapse rate).

What lapse rates must be compared for stability

ELR vs DALR or SALR.

If ELR is greater than DALR, is the air stable or unstable

Unstable. (Slide does not answer; aviation rule provided.)

If ELR is less than SALR, is the air stable or unstable

Stable. (Aviation answer added.)

If ELR is between DALR and SALR, what type of stability

Conditionally unstable. (Added question.)

What is the albedo effect

Darker surfaces absorb more solar radiation.

What type of surface has highest albedo

Fresh snow.

What type of surface has lowest albedo

Asphalt or dark soil.

What happens when winds converge at the center of a low

Air is forced upward, cools, and expands.

Which cooling method is responsible for most cloud formation

Adiabatic cooling.

Which lifting method is most common on windy days over rough terrain

Mechanical turbulence.

Which lifting method generates lenticular clouds

Orographic lift. (Added aviation knowledge)

What does convection typically create

Cumulus clouds.

Why does rising air cool

Decreasing pressure causes expansion.

Why does descending air warm

Increasing pressure causes compression.

What determines cloud base height

Temperature–dewpoint spread. (Added aviation knowledge)