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HIGHER GEOGRAPHY

PHYSICAL CORE

ATMOSPHEREATMOSPHERE

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GMTs

describe and interpret climate maps, diagrams and graphs

construct and analyse climate graphs

describe and explain climate graphs

comment on the accuracy of statements which describe climate patternsshown on maps etc.

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By the end of this topic you should be able to:

explain with the aid of an annotated diagram, why Tropical latitudes receive more of thesun’s energy than Polar regions

explain why there is a net gain of solar region in the Tropical latitudes and a net loss towards the poles

describe the role of atmospheric circulation in the redistribution of energy over the globe

describe and explain the earth’s energy exchanges shown on a diagram

describe the factors which affect the amount of sunlight reflected from the earth’s surface

describe and account for the generalised pattern of atmospheric circulation and globalwinds, or ocean currents shown on a world map

describe the variations in world temperature for the last 100 years (shown eg. on a graph)and suggest both physical and human reasons for these variations

describe and explain the origin, nature and weather characteristics of Tropical Maritime (mT)and Tropical Continental (cT) air masses which affect West Africa

with reference to the Inter-Tropical Convergence Zone and the movement of air masses,describe and account for the variations in West African rainfall.

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0º Equator 90º Pole

LP 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

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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

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This was later improved and a three cell modelwas developed.

The single cell model of atmospheric circulationwas 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 bean oversimplification of reality.

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ITCZ = Inter-tropical convergence Zone (Low Pressure)

STH = Sub-tropical High (High Pressure)

HADLEY CELL ITCZ

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0º Equator 90º Pole30º 60º

LP HP LP HP

Hadley Cell

Polar Cell

Ferrel Cell

THREE CELL MODEL

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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

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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.

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0º Equator 90º Pole30º 60º

LP HP LP HP

conv

erge

nce

dive

rgen

ce

conv

erge

nce

dive

rgen

ce

winds blow from high pressure zones to low pressure zones

WINDS

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CONVERGENCE and …………DIVERGENCE

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