Lecture 1/2 - Introduction & Structure to Ocean-Atmosphere System

Question 1

Heat is transferred by:

Answer 1

Conduction
Convection – free or forced
Advection - horizontal transport of heat by oceans and atmosphere

Question 2

What are the two types of heat?

Answer 2

Sensible – heat we can feel
Latent – heat absorbed/released in changing state. In evaporation lots of heat required to turn water into a vapour. This ‘latent heat’ is taken from the surface of the oceans.

Question 3

What is evaporation, and what is it governed by?

Answer 3

Evaporation is the method by which the atmosphere takes up moisture.

Governed by:

1. ) Amount of moisture in the air
2. ) Availability of moisture
3. ) Availability of heat energy
4. ) Wind – refreshes air supply and allows more evaporation

Question 4

What is vapour pressure (e)?

Answer 4

Vapour pressure (e) represents the actual amount of vapour in the air at any given time

Question 5

What is the saturated vapour pressure (es)?

Answer 5

Saturated vapour pressure (es) represents the maximum amount of water vapour that a parcel of air can possibly hold.

Question 6

The higher the temperature, the higher the saturated vapour pressure (es). What does this mean?

Answer 6

This means that warm air can hold more moisture than cold air. Therefore warm airstreams are usually moist and cold ones usually dry (contain little moisture). Water will continue to evaporate until e = es, until ‘saturated’.

Question 7

What is relative humidity?

Answer 7

Relative humidity RH is the ratio of actual moisture to the maximum moisture content. Given by e/es x 100%

Question 8

When does condensation occur?

Answer 8

Condensation occurs when the air is saturated ie e = es and the RH = 100%.

Question 9

What is the Dew Point Temperature (Td)?

Answer 9

The ground temperature at which condensation occurs. Warm, moist airstreams have high dew point temperatures and cool dry airstreams have lower dew point temperatures.

Question 10

What ways can condensation occur?

Answer 10

Condensation can occur by:

1. ) Cooling at constant pressure
2. ) Cooling by lifting until condensation occurs
3. ) Adding more moisture to the air parcel – eg over the subtropical oceans where large bodies of air are near stationary.

Question 11

What is an adiabatic process?

Answer 11

An adiabatic process is a process that occurs without the transfer of heat or matter between a system and its surroundings.

Question 12

Whats different about cooling in an adiabatic process?

Answer 12

It is assumed that there is no exchange with surroundings. As it cools, the actual amount of moisture contained remains constant (e) but the maximum amount it can hold (es) decreases with decreasing temperature. Eventually e = es and condensation will occur.

Question 13

What is the Dry Adiabatic Lapse Rate (DALR)?

Answer 13

The rate at which dry (unsaturated) air cools with height is the dry adiabatic lapse rate
DALR = 9.8C/Km

Question 14

What is the SALR?

Answer 14

The saturated adiabatic lapse rate.
Once the air is saturated it releases latent heat which slows the rate of cooling such that the SALR varies with moisture content bust, that is usually assumed to be around 2C/Km.

Question 15

What is the Environmental Lapse Rate?

Answer 15

The actual rate at which the atmosphere cools is the (ELR). Measured by a satellite and represents the true state of the atmosphere at a given time.

Question 16

By comparing the rate of cooling of an air parcel to the ELR we can establish whether the atmosphere is stable or unstable. What results show stable and unstable?

Answer 16

If DALR>ELR the air is stable (an air parcel is cooling more quickly than the air around it)

If DALR<ELR the air is unstable (an air parcel is cooling less quickly than the air around it)

Question 17

In what instance can air become stable/unstable?

Answer 17

Air can become unstable if it is heated from below, and stable if it is cooled from below.
Air can also become unstable if the air is cooled from above.

Question 18

When does conditional instability occur?

Answer 18

Conditional instability occurs when an air parcel is stable when dry but unstable when saturated.

Question 19

What is the thermocline?

Answer 19

A thermocline is a thin but distinct layer (in a large body of water or in the atmosphere) in which temperature changes more rapidly with depth than it does in the layers above or below.