Chapter 2B: Heat Transfer

Question 1

What is conduction?

Answer 1

Conduction is the molecular transfer of heat from warm to cold regions.

Question 2

Is air a good heat conductor (i.e. is it good at conduction?)

Answer 2

No, air is a poor conductor → This means that most of the heat transfer in the atmosphere is NOT through conduction.

Question 3

What is convection?

Answer 3

Convection is the transfer of heat by mass movement within a fluid. (collective mvt of larger portions of a fluid, not just single molecules)

Question 4

What is advection?

Answer 4

Advection is transfer by bulk air motion; mostly horizontal transport by the wind.

Question 5

What is “atmospheric” convection?

Answer 5

“Atmospheric” convection is the turbulent vertical circulations driven by buoyancy (density) differences of air parcels.

Question 6

Define an air parcel.

Answer 6

An air parcel is a coherent sample of air that moves freely but does not exchange heat with its surroundings. It maintains the same pressure (but not temperature or density) as its surroundings at the same height.

Question 7

Do warmer air parcels sink or rise?

Answer 7

They rise; warmer air parcels are less dense (or positively buoyant) in comparison to colder surrounding air parcels, which let them rise.

Question 8

Do colder air parcels sink or rise?

Answer 8

They sink; air parcels colder than the air in their surroundings are more dense (or negatively buoyant) which makes them sink.

Question 9

An air parcel is less dense that the surrounding air. Is it warmer or colder than its surroundings?

Answer 9

The air parcel is warmer than its surroundings.

Question 10

An air parcel is more dense that the surrounding air. Is it warmer or colder than its surroundings?

Answer 10

The air parcel is colder than its surroundings.

Question 11

What is a thermal?

Answer 11

A thermal is a rising bubble of air that carries sensible heat upward by convection.

Question 12

Explain what happens in response to daytime solar heating / convection circulation.

Answer 12

• The air near the surface warms by conduction and expands slightly (its gets less dense)
• The hottest air parcels are the least dense and most buoyant; they rise as thermals.
• Cooler and denser air sinks in response to take the hottest air parcels place at the surface

Question 13

What is an adiabatic process?

Answer 13

An adiabatic process is a process with no heat exchange. Ex for an air parcel; there would be no heat exchange between the parcel and its surroundings.

Question 14

Why do rising branches of thermal cells cool?

Answer 14

• Air parcels in rising branches move into lower pressure areas (higher alitutdes)
• To equilibrate pressure with their surroundings they must expand
• This takes work which, from conservation of energy, causes a loss of internal energy and results in cooling.

Question 15

When an air parcel rises 1km adiabatically, how much is its temperature expected to change?

Answer 15

Its temperature will decrease by about 10 K.

Question 16

Why do sinking branches of thermal cells warm?

Answer 16

• Air parcels move into a higher pressure area (lower altitude)
• The atmosphere does work on the parcel to compress it, so the temperature of the parcel increases.

Question 17

When is there warm advection?

Answer 17

When air moves from warm air to cold air;

There is a component of the mean wind down the temperature gradient.

Question 18

When is there cold advection?

Answer 18

When air moves from cold air to warm air;

There is a component of the mean wind up the temperature gradient.

Question 19

What is wind chill?

Answer 19

Wind chill is the increased heat loss due to the presence of wind.