What is geography?
It is the study of MAN (human beings) and his environment and how he uses the environment to earn a living (get development).
Origin of Geography?
Geography = Geo = Greek word = Earth
Graphy = Greek word = Description
Geography is as old as man himself.
Man found himself in the environment.
The environment was hostile (not friendly) because it did not provide basic equipment of man without struggle. The man had no food, no clothes, and no shelter. Man had to struggle to obtain his basic requirements from the environment. He started to locate things in the environment and that is learning geography.
What are the components of man’s environment?
The environment has 4 spheres:-
Why do we learn Geography?
We learn Geography:
Branches of Geography
There are 3 main branches.
How can one acquire Geographical knowledge?
We can learn Geography in the following ways:-
The Solar System
Solar – Sun
What is solar system?
Solar system is the arrangement of the planets and other heavenly bodies that go around the sun.
Members of the solar system:
The planets are traveling around the sun in anti-clockwise direction. The path the planets take is called its orbit. The orbit is oval shape or elliptical.
The sun is the central body in the solar system.
It is the only body which generates its own heat and light
The sun is a star and like many other stars we see in the sky.
The sun seems to be bigger than other stars because it is closer to the earth than the other stars.
Features about the sun
The volume is 10 million times than that of the earth.
It’s diameter is 1.4 million kms.
The sun is not solid, it is gaseous. There are 3 main components:
The sun is very hot.
The surface temperature is almost 6000 degrees Celsius.
The temperature increases towards the centre of where it is about 14 million degrees Celsius.
It is the main source of heat and light for the planets and other heavenly bodies.
What is energy?
It is power to generate heat and make things move or change the energy.
Energy from the sun is called solar energy.
Uses of solar energy:
– No rainfall without solar energy.
For Tanzania, solar energy is the most appropriate alteration source energy because:-
Disadvantages of Solar Energy
What is a planet?
It is a heavenly body that revolves around the sun.
What are the characteristics of a planet?
Pluto does not qualify to be called a planet because its orbit overlaps that of Neptune.
There are 8 planets. Their relative distance from the sun as follows:
1) Mercury 5) Jupiter
2) Venus 6) Saturn
3) Earth 7) Uranus
4) Mars 8) Neptune
Between Mars and Jupiter there are many heavenly bodies known as asteroids.
Note: The larger the distance a planet is from the sun, the colder it becomes.
Other heavenly bodies in the solar system
These are heavenly bodies which revolve around the planets. Not all planets have satellites and the number of satellites varies from planet to planet.
These are heavenly bodies which go around the sun.
They are mostly found between Mars and Jupiter.
They are small and can only be seen through telescopes.
They are solid objects with leading heads and a long tail. These can only be seen when their orbit overlaps that of the earth.
These are pieces of hard matter falling from outer space.
They are visible only when they come near earth.
If they reach the atmosphere the friction effect makes them hot and they break up. If some pieces reach the surface they are called METEORITES. They are made up of nickel + iron.
Meteorites have been seen in various parts of earth.
It is a natural satellite of the earth.
Shape – Is spherical in shape like other heavenly bodies.
Size – Diameter – 3456 km which is about ¼ of the earth’s diameter.
– Mass 1/8 of the earths.
Nature – It is solid and reflects light.
Revolves around the earth and complete one revolution in 29 ¼ days
It also spins along its own axis. The time taken to complete one rotation is the same as that of the revolution.
The moon shows different shapes in a month
Circle (full moon)
It is the planet in which we live.
Origin of the Earth?
– Big bang.
– Created by God.
– The sun – Broken material from the sun started to whirl around the sun. With time it cooled and solidified and formed the planets and other heavenly bodies which revolve around the sun. Our earth is one of them.
The shape of the earth.
They thought the earth was flat. This is wrong. Today we know the earth is spherical in shape. It is not a perfect sphere but oblate spherical or GEOID.
Why along the equator it bulges and at the poles it is slightly flattened. This can be proved by the measurements below:-
Proofs of the spherical shape of the earth
When observing a ship approaching a harbor you don’t see the whole ship at once. You first see the flag post then the whole ship. If the earth were flat then the whole ship would be seen all the time.
The earth is rotating along its own axis from the south place on the east, experience sunrise earlier than places in the west because of the spherical shape of the earth.
If one starts from point O and travels straight to the east, then comes back to point O from the west.
These are photographs taken from space by satellites.
These photographs show the curvature of the earth (curve part of the earth).
This occurs when the earth is between the moon and the sun.
The shadow of the earth which falls on the moon is circular in shape. Only spherical bodies can give round shadows.
All planets are spherical in shape. The earth is a planet. Therefore, it must be spherical in shape.
The movement of earth
The earth is in motion all the time.
Why don’t we see the objects in motion?
We are also in the same motion.
Types of earth’s motions:-
It is the spinning or movement of a body along its axis.
The earth rotates along its axis.
What is the earth’s axis?
It is an imaginary line from North Pole to South Pole through the centre of the earth.
The axis of the earth is not perpendicular to the plane of its orbit. It is inclined at the angle of 66 ½ degrees or 23 1/5degrees from the north perpendicular.
The earth completes one rotation in 24 hours or 1 day.
The Earth’s axis
The rotation of the earth along its own axis is from west to east.
Observation to prove that the earth rotates from west to east:-
A) Effects of Earth’s Rotation
1) Day and Night
The shape of the earth is spherical, so as it rotates along to its axis the side which faces the sun is daytime while the opposite side is night.
Twice a day the level of the sea rises and twice a day the level of the sea falls. This is the result of the earth’s rotation.
Winds are deflected to the right in the northern hemisphere and to the southern hemisphere.
1) What is revolution?
Is a motion of one body around the other.
The earth moves around the sun and completes one orbit in 365 ¼ days.
The orbit of the earth is elliptical in shape, therefore the distance of the earth from the sun varies from place to place.
This is the farthest distance of the earth from the sun which is 152 million kms. This occurs every year on 4th July.
This is when the earth is closest to the sun when it is about 147.3 million kms. This occurs on 3rd January.
The speed of Revolution
The earth takes 365 ¼ days for one revolution. The speed is about 29.6km/sec. ¼ a day is difficult to record one year is either 365 days or 366 days.
After every 4 years we add 1 day. We say that is in a LEAP year where the number of days is 366. The day is added in February.
They result from the earth on its orbit around the sun
There are four seasons
2.The variation of the length of day and night
Places along the equator experience equal day and night
3.The changing position of midday sun at different times of the year
A)Equinox – Twice a year the sun is overhead along the equator. This appears on 21st march and 23 September .This is called equinox and day and night are equal throughout the world.
b) Solstice – On 21st June the midday sun is over headed along the tropic of cancer .This is called summer solstice in the northern hemisphere , in the southern hemisphere it is winter solstice.
On 22nd December, the sun is over head on tropic of Capricorn. It is summer solstice in the southern hemisphere and, and winter solstice in northern hemisphere
It occurs when one heavenly body in space moves between two others, one of them being source of light.
There are 2 types of Eclipse
1) Eclipse of moon (Lunar)
2) Eclipse of sun (solar)
1) Eclipse of moon (lunar)
Occurs when earth frames between the moon and sun and projects the shadow of earth on moon.
2) Eclipse of the sun
Occurs when moon passes between sun and earth and costs shadow on earth.
1) Eclipse can be partial only part of heavenly body is observed.
2) Penumbra – refers to part of the shadow which results when source of high is partially obstructed.
3) Umbra – Refers to part of the shadow in which the light source is totally blocked.
Location of places on earth’s surface
They are imaginary lines on maps from west to east.
These are angular distances north and south of the equator measured from center of earth.
It is the half way between north and South Pole.
The line divides the earth to northern and southern hemisphere latitudes are expressed in degrees, minutes and seconds.
Parallels of latitudes
Are lines drawn north or south of equator parallel to it are called parallel of latitudes.
Are imaginary lines which run from North Pole to South Pole.
They measure angular distances east and west of the prime meridian. Longitudes run from North Pole to South Pole.
Greenwich meridian is chosen as prime meridian and given the value of 0° longitude. In England it passes though Greenwich observatory station and in Africa it passes through Accra in Ghana .
Greenwich meridian divides earth into Western and Eastern hemisphere longitudes measure E or W of this line 0°-180°e.0°-180°w therefore 180°w and 180°e are one and the same longitude.
Importance of latitude and longitudes
Latitudes and longitudes can be used to locate position of places on earth.
NB: When locating positions of places start with latitudes then longitudes.
A great circle is any circle around the earth whose radius is the center of earth.
Any other circle whose radius is not the center of the earth makes a small circle.
The equator is the only line of latitude which is great circle. All parallel latitudes make small circles all longitudes make great circles.
Longitudes and time
Local time : Time recorded along the some meridian is called local time .
NB: When it is midday along a certain meridian: places on the east have afternoon (P.M) and places on the west of the meridian have meaning (A.M)
The prime meridian is the starting point of the time zones. Time is recorded along Greenwich meridian, is called Greenwich Meridian Time (G.M.T.).
The International Date Line (I.D.L)
This is the line of longitude where the calendar day begins Nations have agreed to change dates.
I.D.L – follows the meridian 180
IDL : is not straight it is zigzag .When you cross the IDL west wards you lose a day and when you cross the IDL east wards you add a day.
Globe is the model of the earth, showing the surface of the earth. The surface of earth is made up of two parts. They are:
1) The continents
2) The oceans
It is a large landmark rising from the ocean floor which includes adjacent islands. Continents are surrounded by oceans.
Origins of continent
Originally there was a large land mark called PANGEA.
Pangaea broke into two large land masses which were LAURASIA and GONDWANALAND, These were separated by a thin sea called TETHYS. Later the two large continents broke into several continents which started to drift apart to their present position relative to one another.
Number of Continents
There are 7 continents, they are:
3) North America
4) South America
There are 5 oceans
1) Pacific ocean
2) Atlantic ocean
3) Indian ocean
4) Arctic ocean
5) Southern ocean
NB: There is more land marks in the northern hemisphere and more water bodies in the southern hemisphere.
Location and sizes of Continents
Area: 422mill km
Latitude extended from 0° to 67° north of equator.
Longitudes extend from 100° to 30°.
Borders: North- Arctic Ocean
South – Indian Ocean
East – Pacific Ocean
West –Ural Mountains
NB: Area is separated from Africa by a narrow isthmus of Suez where the Suez canal was dug.
Area: 303mil. Km
Location: Mostly centrally placed among the continents. It is crossed by the equator, the two troops of Cancer and Capricorn and the prime meridian.
Latitudes Extends from 35°S to 37°N
Longitude extends from 150°W to 50°E
Borders: North – Mediterranean sea
South – No border
West – Atlantic Ocean
East – Indian Ocean
3) North America
Size: Third largest continent
Location: Latitude from 10° to 65° north and the ocean
Longitude from 60° to 160° west
Borders: North – Arctic ocean
East – Atlantic Ocean
South – No borders
West – Pacific Ocean
NB: In the south, North America is connected to South America by a narrow step of land called Isthmus of Panama where the Panama Canal was dug.
4) South American
Size : Fourth largest continent
Area – it is about 17.4mil. km2
Location: Latitudes from 40N to 50S and the ocean
Longitude from 35W to 80E
Borders:North: No Borders
South: No borders
West: Pacific Ocean
Size: Fifth largest continent
Location: It is within the Antarctic Circle which is 650S
It is surrounded by the southern ocean
It is only uninhabited continent.
Size: Sixth largest continent
Location: Latitude from 40°N to 40°S
Longitude from 10°E to 60°W
Borders: North – Arctic ocean
East – No Borders
South – Mediterranean Sea
West – Atlantic Ocean
Size: Smallest continent
Location: Latitude from 40°N to 10°S north and the ocean
Longitude from 115°E to 150°W
Borders: North – Indian ocean
East – Pacific Ocean
South – Southern ocean
West – Indian Ocean
Relief Features on Continent
The surface of continent is not flat.
There are many Relief features: Mountains,plains, valleys,hills and plateaus.
Extensive highland with more flat top.
They have steep sides.
How are plateaus formed?
In areas of faulting compressional forces can uplift the land between fault lines.
Lava-flow fissure eruptions give lava plateaus.
Are extensive flat lowland. Low elevation 0-220km above sea level.
How are they formed? By down pushing of earth’s crust.
3) Mountains and Hills
Mountains are high and large .Hills are small and short.
A mountain is a land form which has high relief of more than 300m above the surrounding
Types of Mountains
1) Volcanic Mountains
2) Residual Mountains
3) Block Mountains
4) Fold Mountains
1) Fold Mountains
They are formed by wrinkling of the earth’s rock layers.
When rock layers are subjected to compression they form series of folds.
The up fold form series of Fold Mountains. Fold Mountains are extensive, covering thousands of kms across continents.
Example:- Africa – Atlas – South Africa
They are raised lands above the surroundings with flat top with steep sides. They are formed in areas of faulting.
They are fold by compression or tension.
(a) Rocks layers subjected to compression.
(b) Parallel faults develop.
(c) The middle block between the parallel faults is squeezed to form a horst.
Block Mountains by Tension ( )
(a) Rocks layers subjected to tensional force.
(b) Parallel faults develop.
(c) The side blocks sink leaving the middle block between parallel faults higher on Block Mountains.
Examples of Block mountains:- Europe = Vorges, Black forest
This is trough like depression with steep sides and flat bottom which is found in areas of faulting.
How is it formed? It can be formed by: (i) Compression (ii) Tension
(i) By Compression
(a) Rocks layers subjected to compression.
(b) Development of parallel faults.
(c) The side block moves upward. The middle block remains stable.
(ii) By Tension
(a) Rocks layers subjected to tensional force.
(b) Parallel faults develop.
(c) The middle block sinks creating a rift valley.
Example of Rift Valley:- The Great African Rift Valley.
It is part of the Great Rift Valley which starts from the Middle East and moves southwards to river Zambezi. When it comes to East Africa, it splits into 2 branches:-
(i) The Eastern Branch
When the eastern branch enters Kenya, it is marked by the position of (a) Lk. Turkana (b) L. Naivasha (c) Lk. Magadi
In Tanzania:- (a) Lk. Natron (b) Lk. Manyara (c) Lk. Eyasi (d) Lk. Nyasa
(ii) The Western Branch
From Lk. Nyasa the western branch begins. This is marked by the following lakes:-
(a) Lk. Tanganyika (b) Lk. Kivu (c) Lk. Albert (d) Lk. Edward
The western branch disappears in northern Uganda.
Note: Lake Victoria and Lake Kyoga are not rift valley lakes.
They are formed by piling of lava around a vent.
Volcanic mountains can be put into 3 groups:
(i) Active Volcano – Recently erupted. E.g. Oldonyo Lengai (Serengeti, Arusha)
(ii) Dormant Volcano – It has erupted in historical times but has remained inactive for a long time. E.g. Mt. Vesuvius (Naples, Italy)
(iii) Extinct Volcano – It has not erupted in historical times and does not show signs of erupting again. E.g. Mount Elgon (Uganda)
Basins and Drainage of Continents
Drainage is the removal of water from land.
Basins refer to the forms of natural or artificial depression varying in size in the Earth’s surface.
Basins sometimes can be occupied by water. Therefore, they form river, lakes and ocean basins.
Some depressions or hollows do not contain water e.g.the basins in the mining area.
The rain water land surface area can be removed by various ways:
(i) Some water evaporates into the air.
(ii) Some water flows on the ground surface.
Define the following:-
River is a mass of water flowing in a natural channel over the earth’s surface. All rivers flow from highlands to lowlands.
All the tributaries, the main river and distributaries together form river system.
A place where the river makes its first appearance.
This can be high in mountains. E.g. River Rufiji – Southern highlands
Rivers which start from lakes. E.g. River Nile – Lake Victoria
Rivers can even start from springs.
Place where a river ends. This can be sea or ocean etc. E.g. Rufiji.
Inland Drainage Basins
Basins which collect water but have no outlets. In such basins the water will be salty. E.g. The Great Rift Valley.
Some lakes have outlets e.g. Lake Kyoga, Lake Victoria.
Big Rivers of the world
|1||Nile||Lake Victoria||Mediterranean Sea|
|2||Congo||Chambesi River||Atlantic Ocean|
|4||Zambezi||Victoria falls||Atlantic Ocean|
|7||Brahmaputra||Southwest Tibet||Bay of Bengal|
|8||Mississippi||Lake Michigan||Gulf of Mexico|
|9||Amazon||Apacheta Cliff||Atlantic Ocean|
|10||Rhine||Swiss Alps||Rotter Dam|
|11||Huang ho||Bayan Har Mts||Bohaisea|
|12||Yang Tse Kiang||Ngari||Mt. Damjak Kabub|
Ocean is a large body of water surrounding lands.
Major oceans of the world:-
(i) Pacific Ocean – 165.3 million km2
(ii) Atlantic Ocean – 82.2 million km2
(iii) Indian Ocean – 73.4 million km2
Note: Oceans have no uniform distribution on the earth’s surface. There are more natural bodies in the S. Hemisphere than in the N. Hemisphere.
Nature of Ocean Water
Ocean water is salty, it contains mineral salts. Major salts in the ocean water are:-
(a) Sodium Chloride
(b) Calcium Carbonate
(c) Magnesium Sulphate
(d) Other potassium
What is the origin of salts in oceans?
Rivers from continent empties its water into the oceans.
Evaporation takes place leaving behind the salts.
Seas/Oceans do not have outlets. Therefore, long term accommodation of salts in oceans causes the salinity of ocean water. Salinity is the number of solid material in grams which is left when 1000g or 1 litre of sea is evaporated. Salinity is expressed in gms per thousand.
Salt concentration in ocean is not uniform. It varies from ocean to ocean and within one ocean.
Tropical regions have highest concentration because of excessive evaporation. Equatorial regions salinity is less. Towards the poles salinity decreases.
Temperature of ocean water is not uniform. Normally temperature decreases towards the poles. Example: Around the equator temperature can be 25 degrees Celsius and at the pole it can drop to 2 degrees Celsius.
Ocean water is constantly in motion. The two types of movement:-
(i) Horizontal Movement = Ocean currents and tides.
(ii) Vertical Movements = Surface water sinks and subsurface water rises.
This is caused by temperature and density of water.
Horizontal movement of surface water in the oceans.
They are mainly caused by wind. We refer to dominant wind:- Polar winds, Westernlies, Trade winds.
The direction of movement of ocean currents is influenced by three factors:-
(i) Direction of dominant winds.
(ii) Rotation of the earth – deflection of ocean currents to the right in the northern hemisphere and to the left in the southern hemisphere.
(iii) The shape of the continent – When the current meet a large land mass they split and change direction.
Note: The circulation in the northern hemisphere is clockwise and in the southern hemisphere it’s anticlockwise.
Types of Ocean Currents
Originate from warm climate and flow polewards. E.g. Agulhas, Brazil.
Originate from cold regions and flow towards the equator. E.g. Benguela, Peru.
The rising and falling of the level of water in oceans. Twice a day the level of the ocean rises known as high tides. Twice a day the sea level falls which is called low tides.
Causes of tides
Gravitational pull of the sun and the moon. The pulling force is not the same all times.
Spring Tides – When the sun, the moon and the earth are in a straight line, the pulling force is maximum therefore we have the greatest high tide called spring tide.
Neap Tides – When the three bodies are in right angle, the pulling force is less so we have neap tides.
These are surface disturbances.
Causes of waves
Most ocean waves are caused by wind. That is why when it is calm, the waves are little, and when it is windy the waves are great.
A wave has got the following features:
(a) Crest – The highest part of a wave.
(b) Trough – The lowest part of a wave.
(c) Length – The horizontal distance from the crest to the next.
(d) Height – The vertical distance from the crest to the trough.
(e) Period of wave length – The time taken by wave to complete one wave length.
Nature of Ocean Floor
The ocean floor is not flat like a classroom floor. It has got various relief features like plain, valleys, hills etc.
Features on the Ocean Floor
A gentle slopping margin of a continent. It is a shallow water extending from the coast to about 200m towards the sea. The continental shelf floor provides excellent conditions for breeding of sea organisms like fish.
This is a steep slope from the edge of continental shelf to deep ocean plains.
A fairly even extensive plains which have depth between 2000m to 3000m. The plains are mostly covered by mud.
These are saved parts of the ocean floor. Example mud ocean ridges. Some raised parts make plateaus.
Note: If the raised part reaches above water level it forms oceanic island.
If an island rises from continental shelf it forms continental island e.g. Zanzibar.
These are narrow and deep depressions on the deep ocean plains. Some trenches are very deep to over 10,000m. E.g. Mariana Trench is 11,035m.
It is the condition of the atmosphere at a particular place observed over a short period of time. Time can be an hour, a day or a week.
Elements of Weather
Weather of a place is obtained by measuring the elements of weather. There are 7 examples of weather. They are:-
(a) Temperature (d) Rainfall (g) Cloud Cover
(b) Humidity (e) Sunshine
(c) Pressure (f) Wind
Measuring the Elements of Weather
It is a place where weather elements are measured and recorded. Weather measuring instruments are kept at a weather station. These include:
|Sunshine||Campbell Sunshine Recorder|
|Wind||Anemometer/ Wind vane|
It is the average weather condition of a particular place observed over a long period of time. The time can be over 30 years.
Note: The elements of climate are the same as those of weather.
What is temperature?
Is the degree of heat in a body?
How do we measure temperature?
By using thermometer – it is expressed in degrees Centigrade or Fahrenheit.
Types of Thermometer
|Wet bulb Thermometer|
|Dry bulb Thermometer|
It is a wooden box where thermometers are kept. It has 4 sides which are built to allow circulation of air. The box is painted white to improve insulation. It has a double roof to prevent direct sun rays
The instruments kept in Stevenson Screen are:-
(a) Minimum Thermometer
(b) Maximum Thermometer
(c) Dry bulb Thermometer
(d) Wet bulb Thermometer
Used to measure the lowest temperature in a day. (24 hrs)
Minimum Thermometer is made up of a glass rod with a bulb at one end which contains alcohol in it. Alcohol is used because it has a low boiling point.
How it works
When temperature falls the alcohol contracts and the meniscus pulls the metal index down along the tube. When temperature rises, alcohol expands and rises but the metal index remains at the lowest temperature point. Readings are taken on the part of the metal index nearest to the meniscus.
Maximum Thermometer is made up of a glass tube with a bulb at one end containing mercury and has a metal index.
How it works
When temperature rises, mercury expands and the length of mercury column increases and pushes the metal index up the glass tube. When temperature falls, the mercury column contracts leaving the metal index up in the glass tube. Maximum temperature is obtained by reading the scale from the side of the metal index nearest to the mercury.
Note: After reading is done the metal index is returned to the mercury by a magnet.
It is used to measure maximum and minimum temperatures of a day at the same time. It is made up of a U-shaped glass tube. It has mercury, alcohol and metal index inside.
How it works
When temperature rises the alcohol in the left hand limb expands and pushes mercury column down the left hand limb and up the right hand limb.
Uses of Maximum and Minimum Temperature figures
Max and Min temperatures of a day can be used for the following:
Is the average of maximum and minimum temperature of the day.
Mean Daily Temp = Min+Max
2. Daily Range Temperature
This is the difference between the maximum and minimum temperature.
Daily Range = Max – Min
3. Mean Monthly Temperature
This is the sum of the Daily Mean Temperature for one month divide by number of days in a month.
Mean Monthly Temperature = Add all Mean Daily Temperature in a month
No. of days in a month
4. Mean Monthly Range
Is the difference between the highest Mean Daily Temperature and the lowest Mean Daily Temperature.
Mean Monthly Range = Highest Mean Daily Temperature – Lowest Mean Daily Temperature
5. Mean Annual Temperature = Sum of Mean Monthly Temp
6. Annual Range of Temperature = Highest Mean Daily Temp – Lowest Mean Monthly Temp
The mean temperature of DSM for January can be obtained by adding all January Mean Temperature for a period of 30 years and divide by the number of years of observation.
Mean Monthly Temp = y1 + y2 + y3 +…….y30
Mean Monthly Temp for a certain month i.e. January for different places can be shown on a map. Lines joining places with the same temperature are called ISOTHERMS.
Mean Monthly Temperature for a particular month e.g. January for different stations can be plotted on a map.
y1 + y2 + y3 +…….y30
All points with the same temperature are joined with a line. This line is called ISOTHERM.
Isotherm is a line which joins all places with the same Mean Monthly Temp.
There are two common scales:
– Fahrenheit Scale (°F)
It is based on the boiling point of water which is 212° and freezing point which is 32°.
– Centigrade (Celsius) Scale
It is based on boiling point of water which is 100° and freezing point which is 0°.
Factors Affecting Temperature
It is the height of a place above mean sea level.
Temperature decreases with increase in altitude.
The rate of change is 0.6° for every 100mts rise, or 3.6° for 1000m rise.
Temperature decreases with increase in latitude. From the equator temperature decreases polewards.
Rays A and B are equal rays falling on different latitudes on the earth’s surface.
Ray A is received on the earth’s surface at a high angle. It is spread over a small area therefore higher temperature.
Ray B falls on a surface at low angle and is spread over a large area therefore low temperature.
Secondly, Ray A has traveled a shorter distance through the atmosphere and less insulation is lost therefore more heat along the equator which rises the temperature.
Ray B has traveled a longer distance through the atmosphere therefore more insulation is lost and so less heat at high altitude and low temperature.
They influence the temperature of the coastal areas.
How: Two types of Ocean Currents:
(i) Warm Ocean Currents
(ii) Cold Ocean Currents
Winds blowing over warm ocean currents transport the temperature of ocean current to adjacent coastal land. E.g. Along East Africa, warm Mozambique currents raise the temperature of the coastal areas. While in South Africa, cold Banguela currents lower the temperature of coastal areas.
Places which are far away from seas or ocean show great range of temperature because they do not have the moderating effects of oceans/seas.
It is the moisture content in the atmosphere. It is in form of water vapour which is in gas state which makes it colourless like other gases.
Sources of moisture:-
(i) Evaporation (ii) Evapo-transpiration
Humidity is measured with an instrument called Hygrometer. It has two ordinary thermometers. One is wrapped in muslin cloth which is dipped in distilled water and the second is not treated in the same way.
How it works
When the air is not saturated, evaporation from the muslin cloth takes place and cools the wet bulb thermometers where the mercury contracts. The two thermometers will record different temperature readings:-
How to express Humidity
It is expressed in grammes/metre2 i.e. the actual amount of water vapour present in a certain volume of air at a given temperature.
Is the amount of water vapour present in a mass of air expressed in percentage of the total amount of vapour that would be present when the air is saturated at the temperature.
Note: Saturated air cannot take additional water molecules at that temperature.
Formula: Relative Humidity = ___Vapour Pressure x 100
Saturated Vapour Pressure
It refers to the fall of moisture from the atmosphere to the earth’s surface. It includes dew, frost, snow, mist, fog, hail, sleet and rain.
– Is formed when small droplets combine together to form large drops.
– When the drops are too heavy to remain in the atmosphere, it falls to the earth as rain.
– Three main processes that make up rainfall:-
(a) Evaporation – Is a process in which water is converted to water vapour.
(b) Condensation – Is a process where water vapour is converted into tiny droplets of water.
– It occurs when water vapour is cooled.
(c) Precipitation – Is the process by which condensed water vapour falls to the ground in various forms such as snowfall.
Are lines on a map joining places with the same precipitation.
Types of Rainfall
– Common in areas with intense heat during day time.
– When heated the moisture is formed and water vapour rises as convectional currents.
– The water vapour condenses into cumulonimbus cloud where finally it falls down as rain.
– This type of rainfall is accompanied by thunder and lightning.
– Is a type of rain formed when large masses of air with different characteristics meet.
– Warm air tends to rise, over cooled air pressure decreases and air expands and cools.
– At high altitude the warm air cools and water vapour condenses to form clouds where it finally rains.
– In tropical regions, two air masses with similar physical properties meet to form tropical cyclone over oceans between latitudes 8°N and 8°S.
– It usually brings heavy rainfall associated with thunderstorm, lightning and very fast moving winds.
Tropical cyclones are known by different names in different areas. E.g. China – Typhoon.
When on shore moist winds are forced to rise up by the presence of a hill or mountain. As the moist air rises, it cools and condenses to form water droplets which fall on to the ground as rain.
The side of the mountain facing the direction of the wind is called WINDWARDSIDE. This side gets plenty of rain. The side of the mountain facing away from the wind is called JEEWARD. This side has less or no rain.
Occurrence –Relief rainfall can occur at any place where mountains or hills are available.
Measurement of Rainfall
The instrument used is Rain gauge.
This consists of:
a) Cylindrical copper container about 12.8cm in diameter.
b) A copper receiver (jar).
c) A funnel which fills the top.
d) A graduated measuring cylinder.
Setting in a rain gauge.
It is set in a weather station where there is open level ground with short grass. It is partly sunk into the ground to reduce evaporation. The other part is about 30cm above the ground to avoid splash.
Reading is taken in a specific time everyday.
What do we do with rainfall data?
To calculate Mean Monthly Temperature for a particular month.
How: Add all temperatures of the month
Number of Days
Rainfall graphs are represented by using bars (Histogram).