1

Energy Receipt and LatitudeRecap

Tasks:

1. Study figure 2.3 (page 7) describe the areas of energy surplus and deficit.

2. Using page 6 give 3 reasons why there is a net gain of energy in the low tropics.

3. Find 3 reasons why the poles are an area of energy deficit.

2

Exam Question - 2002With the aid of an annotated diagram of the earth,

describe and explain the latitudinal variation of the Earth’s energy balance?

Use Figure 2.3 on page 7 to help

What is this question asking?

1. DESCRIBE the variation in solar energy at different latitudes – notably the tropics and polar regions

2. EXPLAIN why this variation occurs – i.e. why does what you are saying to the first part of the question actually happen

3

Global Transfer of Energy

1. What is the global transfer of energy?

2. How does this happen? • Single cell model of atmospheric circulation• Three cell Ferrel model

‘Tropical latitudes receive more solar energy than Polar latitudes. The atmosphere and oceans help to redistribute

this energy to maintain a global energy balance.’Source: Question 1, Higher Geography Paper 1 - 2004

4

In theory an imbalance in energy receipt could result in lower latitudes becoming warmer and higher latitudes becoming even colder.

In reality energy is transferred from lower latitudes (areas of surplus) to higher latitudes (areas of deficit).

How?1. Atmospheric circulation (80% of

heat transfer).2. Ocean Currents.

5

Global Transfer of EnergyWhy do we have transfer of energy?

• Areas above 38° latitude receive less solar energy than those between these latitudes.

• At higher latitudes more energy is emitted from the surface than is absorbed.

• Deficit in energy above 38°.• Surplus between 38° North and South.• If this were too remain the tropics would become

much hotter and higher latitudes much colder.• This does not occur as energy is moved from areas of

surplus to areas of deficit.• This process is known as atmospheric circulation.

6

0º Equator

90º Pole

SURPLUS

DEFICIT

1. ATMOSPHERIC CIRCULATION

2. OCEAN CURRENTS

7

0º Equator 90º Pole

surplus deficit

8

0º Equator 90º Pole

TRANSFER of ENERGY by ATMOSPHERIC CIRCULATION

9

TRANSFER of ENERGY by OCEAN CURRENTS

0º Equator

90º Pole

10

11

0º Equator 90º PoleLP HP

At the Equator the atmosphere is heated Air becomes less dense and rises. Rising air creates low pressure at the equator. Air cools as it rises because of the lapse rate. Air spreads. As air mass cools it increases in density and descends. Descending air creates high pressure at the Poles. Surface winds blow from HP to LP.

SINGLE CELL MODEL

12

warm air is less dense therefore lighter air rises in the Tropics this creates a zone of LOW PRESSURE air spreads N and S of the Equator air cools and sinks over the Poles this is a zone of HIGH PRESSURE air returns as surface WINDS to the Tropics air moves from areas of low pressure to high

13

This was later improved and a three cell modelwas developed.

The single cell model of atmospheric circulation was developed to explain the transfer of energy from the Tropics to the Poles.

Single Cell Model

Today the three cell model is also considered to be

an oversimplification of reality.

14

0º Equator 90º Pole30º 60ºLP HP LP HP

Hadley Cell

Polar Cell

Ferrel Cell

THREE CELL MODEL

BBC Clip - Global Circulation

15

ITCZ = Inter-tropical convergence Zone (Low Pressure)

STH = Sub-tropical High (High Pressure)

Hadley Cell ITCZ

16

Warm air rises at the Equator - Inter-Tropical Convergence Zone (ITCZ). Equatorial air flows to ~30º N then sinks to the surface and returns as a surface flow to the tropics. This is the Hadley cell.

Cold air sinks at the North Pole. It flows S at the surface and is warmed by contact with land/ocean, by 60º N it rises into the atmosphere. This the Polar cell.

Between 60º N and 30º N there is another circulation cell. This is the Ferrel cell.

The Hadley cell and the Polar cell are thermally direct cells.The Ferrel cell is a thermally indirect cell.

Energy Transfer

17

ENERGY TRANSFER

Hadley Cell

Polar Cell

Ferrel Cell

Heat energy is transferred from the Hadley Cell to the Ferrel Cell and from the Ferrel Cell to the Polar Cell.

In this way heat is transferred from the Equator where there is an energy surplus to the Poles where there is an energy deficit.

18

Task:Answer questions 3 and 4 on page 32

Under the heading ‘Energy Transfer and the Atmosphere’

Answers can be found on pages 8 10

19

Global Heat BudgetAtmospheric Circulation: Exam Style Question

Describe the role of atmospheric circulation in the redistribution of energy over the globe.Or Explain how the circulation cells assist in the redistribution of energy over the Earth.

PLAN:Name the cellsDescribe where they start / stopExplain why they operateExplain how air rises, falls Describe the movement of airLearn the concluding sentence – link back to the question.

20

Global Heat BudgetAtmospheric Circulation: Exam Style QuestionEnergy is redistributed across the globe by 3 atmospheric cells – the Hadley, Ferrel and Polar cells.

The Hadley cell is a thermally direct cell that moves energy polewards. Air rises at the equator as it is an area of energy surplus. Air is heated, becomes less dense and begins to rise. As it cools it spreads North and South from the equator. At approximately 30degrees N&S air cools and sinks to the ground. Some of the air is returned as surface winds towards the equator for reheating.

The Polar cell is also thermally direct. Cold, dense air sinks at the poles and moves towards the mid-latitudes as surface winds. At this point it meets air coming upwards from the equator – this creates a zone of convergence and forces air to rise at appox 60degrees. Some of this air returns to the Poles to complete the Polar cell. Some moves to the

equator.

The Ferrel cell is thermally indirect and is driven by movement in the other two cells. It allows warm air from the equator to move polewards and cold air from the Polar cell to move towards the equator. It is in this way that the cells move energy from an area of surplus to an area of deficit and redistribute energy across the globe.