Geography, Climatology, Climate, Weather. This entails the term one grade 12 guide on the concept of climatology

1. 2022
SUBJECT : GEOGRAHY revision manual
GRADE :12
Strand : Climate and weather
Written by: BB SHINGANGE

2. read this…
Noteworthy, this is not a textbook, however a guide which you can consult
with after studying your textbook for further comprehension. In other
words, this is just an additional resource for you to can use in attempting
to gain thorough understanding of some topics you might have found
confusing in your textbook. So, you are bound to study your textbook even
though you have this manual.

3. Important info
The required response for the following
Name
To name means to provide the required information in the form of single words or short sentences
that are preferably numbered.
Define
This requires giving the precise meaning of a concept. Very often definitions have to be
memorised verbatim (word for word).
Explain
An explanation requires that a certain outcome be made clear. Clarify or give reasons for
something, usually in your own words.
Describe
To describe is to say exactly what something is like; to give an account of the characteristics or
nature of something, to explain the way in which something works. No opinion or argument is
usually needed.
Discuss
To discuss is to comment on something in your own words. This often requires debating two
viewpoints or two separate possibilities.
Compare/Contrast
In this case point out the similarities and differences between objects, ideas or points of view.
When you compare two or more objects you should do so systematically – completing one aspect
at a time.
Distinguish
To distinguish means to point out the differences between objects, different ideas or points of
view. This usually implies the use of your own words.
Demonstrate
To demonstrate means to include and discuss examples. You have to prove that you understand
how a process works or how a concept is applied, by giving examples of real-life situations.
Analyse
Analysing means to identify parts or elements of a concept or statement provided and describing
each of the key points.
Criticise
This means that you should indicate whether you agree or disagree with a particular statement or
view. You should then describe what you agree/disagree, with, and give reasons for your view.

4. Glossary
Front The leading edge of an advancing air mass
Warm front The leading edge of an advancing warm air
Cold Front The leading edge of an advancing cold air
mass
Tropical cyclone is a low-pressure cell that develops over warm
oceans between the tropics
Midlatitude cyclone is a low-pressure system that forms when a
cool air mass (cP) collides with a warm, moist
air mass (mT).
Airmass is a distinctive body of air with a homogenous
mix (relatively same mixture) of temperature,
humidity, and stability, and it initially reflects
the characteristics of its source region
cP Stands for continental polar
mT Stands for maritime tropical
Cyclogenesis Is defined as the imbalance in energy between
Polar regions and Tropical regions.
hPa Stands for hectopascals
Storm surge is the seawater that is pushed inland during a
tropical cyclone.

5. Mid-latitude cyclones
I. What is a mid-latitude cyclone?
➢ A Mid-latitude cyclone is a system of low pressure associated with the meeting of warm
and cold airmasses
Or
➢ midlatitude cyclone is a low-pressure system that forms when a cool air mass (cP) collides
with a warm, moist air mass (mT).
NB: know at least one of the two
II. Characteristics of mid-latitude cyclone/s
➢ Also known as a wave cyclone or extratropical cyclone
➢ The two air masses do not mix because they have different temperature and density
➢ They are therefore separated by a zone called a front
➢ There are two fronts in a midlatitude cyclone namely, Warm front and Cold front
➢ Then, what is a front? A front is transition zone between airmasses of different temperature
and humidity
➢ A warm front occurs when warm air is advancing and forced to override (climb over) cold
air.
➢ A cold front occurs when advancing cold air undercuts (wedges in underneath) a body of
warm air.
➢ The diameter of midlatitude cyclones ranges from 1 000 km to 4 000 km
➢ Cyclogenesis is the imbalance in energy between Polar regions and Tropical regions.
Where do mid-latitude cyclones form
➢ Midlatitude cyclones occur between 30◦ and 60◦ north and south of the equator.
➢ They occur mainly over oceans and coastal areas.
➢ These cyclones affect regions between 35◦s and 70◦s in the South Africa.
➢ The southern tip is 37◦, so the cold front only crosses the southern cape.
➢ Cold fronts only reach the interior of South Africa in winter, because during this season all the
pressure belts move slightly north.
• Hence, this is the reason Western cape province have very cold winters.

6. III. Conditions necessary for the formation of Midlatitude cyclones
➢ Two large High-pressure systems in contact on the polar front.
➢ The warm subtropical High pressure contains warm, moist maritime air
➢ The polar high pressure contains cold, dry air mass
➢ The air flow converges from opposite direction on the two sides of the polar front
➢ Disturbances on the polar front result in an unstable situation creating a local low
pressure into which air will flow and around which air will circulate
➢ Stages of development (Midlatitude cyclones)
-Initial stage
-Development/ wave stage
-occluded stage
-Dissipating stage

7. IV. Weather conditions associated with cold front, warm front and occluded
fronts (NB: These are generally “weather conditions associated with mid-latitude cyclones
because all these fronts make up a midlatitude cyclone”)
a) Cold front conditions
A cold front is defined as the leading edge of a cold air mass
➢ Temperature decreases as the cold front passes over
➢ Pressure decreases as the cold front approaches then increases as the cold sector
arrives
➢ Humidity decreases
➢ Warm moist unstable air in the warm sector is lifted up and condensation occur to
form cumulonimbus clouds resulting in thunderstorm and rain
➢ Wind direction changes
This diagram above shows an idealized cold front
This photo shows a typical cold
front

8. b) Warm front conditions
A warm front is defined as the leading edge of a warm air mass
➢ Temperature increases as the warm front passes over
➢ Pressure decreases as the as the warm sector arrives
➢ Humidity increases
➢ Warm moist air is lifted up
➢ Cirrus cloud appears, the altostratus follows, later nimbostratus which brings soft soaking
rain.
The diagram above shows an idealized warm front

9. Tropical cyclones
➢ A Tropical cyclone is a low-pressure cell that develops over warm oceans between
the tropics
i. General characteristics of tropical cyclones
➢ Tropical cyclones are intense low-pressure systems
➢ They originate in late summer and/or Autumn
➢ They need Coriolis force to form
➢ They move westwards 40km- 200km per day, then turn to curve back at (20◦-30◦)
north and south eastwards 500-700 km/day
➢ The rotation is clockwise in the southern hemisphere and anti-clockwise in the
northern hemisphere
➢ Feeding of air at the surfaces is nearly equal to the air leaving the cyclone system
in the upper troposphere
➢ They are accompanied by heavy rains, storm surges and high winds
Where do tropical cyclones form
➢ Tropical cyclones occur between 30◦N and 30◦s
➢ They do not occur between the equator (0◦) and 5◦ because there is no Coriolis force between
0◦-5◦ North and South. (In other words, tropical cyclones occur anywhere between 5◦ -30◦ N
and 5◦ -30◦ South.
➢ They usually occur in the eastern parts of countries because warm ocean currents warm the
eastern sides of countries
➢ In different parts of the world, they are known by different names.

10. ➢ In the Gulf of Mexico, they are known as Hurricanes
➢ In Japan and Eastern China, they are known as Typhoons
➢ In South Africa, they are known as tropical Cyclones
➢ In Australia, they are known as Willy willies/ Tropical cyclones
Conditions necessary for tropical cyclones to form
-warm oceans
-High humidity in the air
-unstable air
-little surface friction
-light variable winds
-low air pressure with closed isobars
-divergence of air in the upper level
Stages of development (Tropical cyclones)
-formative stage
-immature stage
-mature stage

11. -degeneration stage
1. Formative stage
➢ Pressure is still above 1000 hPa
➢ High sea/air temperature
➢ Cirrus, cumulus cloud and light rain
➢ Winds reach gale force—(60km/h)
➢ Small area is influenced (about 20 km from the eye)
2. Immature stage
➢ Air pressure in the eye (centre of the cyclone) fall below 1000 hPa and
still decreasing
➢ The vortex contract and the storm intensify as more evaporation and
condensation occur
➢ Cumulonimbus clouds surround the eye to a height of 12 km up
because the vortex is pushing the clouds
➢ Hurricane wind speed (120km/h) within 50 km from the eye and gale
force winds within 500 km from the eye.
➢ In this stage, a large area is influenced. About 600 km in diameter
3. Mature stage
➢ Air pressure of about 900-940 hPa
➢ Warm moist air still converges, unstable air rises around the centre, air sinks
into the centre at the upper level of the system
➢ Heavy rain from cumulonimbus, 160km from the eye
➢ Hurricane winds (177) extended to 300km from the eye
➢ Worse weather in the active quadrant
➢ This stage can last up to seven days
4. Degenerating stage
➢ at this stage the tropical cyclone reaches the land

12. ➢ Pressure in the eye rises when the land is reached
➢ temperature decreases
➢ less moisture is fed into the system
➢ The wind speed decreases
➢ the area affected shrinks (get reduced drastically)
➢ This is the stage where tropical cyclones die when they reach land (this is due
to friction force posed by trees, building and mountains altogether with the
rough Earth’s surface.
Associated weather conditions
➢ Tropical cyclones cover an area of 500km in diameter
➢ the central part of a tropical cyclone is named or known as the “Eye”, so the sides of the
eye are known as the eye walls
➢ In the eye there is hot, humid, calm weather conditions
➢ In the eyewalls there is rapid uplift of air, which lead to the development of thick
cumulonimbus clouds of over 15 km in height,
➢ This results in heavy rain and thunderstorms.
Shows the eye at the centre of this system and eye walls at the
surrounding of the eye.

13. ➢ beyond the eyewall there is dense cirrus, altostratus and cumulus extends several hundreds
of km, this result in steady rains.
Impacts of tropical cyclones on human activities
➢ flooding wipes away crops
➢ flooding kills livestock
➢
Impacts of tropical cyclones on people
➢ Flooding can destroy homes, leaving thousands of people homeless.
➢ people can drown to death due to flooding
➢ high winds can destroy buildings and cars killing hundreds of people
➢ the hurricane winds can leave hundreds of people injured.
➢
➢
➢
Impacts of tropical cyclones on farming
Negative impacts

14. ➢ flooding can wipe away crops
➢ flooding can wipe away the top fertile soil needed for cultivation
➢ cut off chemical pipes carried away together with water can damage the crops
➢ high pollution of rivers by chemicals poses a threat to the water available for
irrigation
Positive impacts
➢ high amount of rain refills dams or streams for irrigation
➢ enough rain irrigates naturally the crops sowed, saving time.
➢
➢
➢
Impacts of tropical cyclones on farmers
Negative
➢ damaged crops by flooding in their farms will result in them making losses
➢ polluted nearby streams where they used to get water will result in increased
costs for fetching water for irrigation
➢ Small scale farmers will suffer from hunger because they often produce for
self/family consumption
➢ wiped top fertile soil increase financial strain on farmers if they are to continue
farming as they will need to buy tons of manure and it is costly.
➢

15. ➢
➢
➢
Positive impacts
➢ high amount of rain refills their dams or streams for irrigation reducing
farmers’ expenses.
➢ Rain makes it easy for farmers by saving their time for irrigating.
➢ flooding can dump the alluvium from riverbeds on floodplains making
it possible for them to increase production. Note, alluvium boost
fertility.
➢
➢
➢
➢
Impacts of tropical cyclones on infrastructure
➢ high speed (gale force or hurricane) winds can destroy powerlines
➢ Water pipelines can be cut off
➢ High volume of water can destroy bridges
➢
➢
➢
➢

16. Strategies to help prepare for and manage the effect/negative impacts of
tropical cyclones
Strategies to help prepare for a tropical cyclone
• provide the society with websites or other free platforms where they
would get natural disaster warnings or updates
• the civilians should listen to radio and watch Tv for latest updates of
the upcoming severe weather
•
Strategies/precautions/measures to be taken/implemented to help manage the
effect/negative impacts of tropical cyclones
➢ avoid crossing flooded rivers
➢ farmers should move pumps away from rivers
➢ people staying close to rivers should evacuate
➢ small to medium sized boats should remain at ports for few days after a tropical
cyclone
➢
➢
➢
➢

17. Tropical Cyclones: Synoptic weather maps
SUBTROPICAL ANTICYCLONES AND ASSOCIATED WEATHER
1
•Factors
influencing the
climate of SA
2
•SA Berg windy
•NB Line
thunderstorm is
purpusefully
ommited.

18. FACTORS THAT INFLUENCE THE CLIMATE OF SOUTH AFRICA
SOUTH AFRICAN BERG WIND
➢ Berg winds are warm, dry, gusty winds that blow from the SA plateau towards the coast in
winter.
➢ In winter, when there is a strong HP cell over the interior and a LP cell at the coast (coastal
LP), wind spirals downwards and outwards around the HP.
➢ As the wind descends from the plateau to the coast, it is heated by compression, arriving at
the coast as a hot, dry wind (sometimes over 35 ºC) and can last for two or three days.
➢ Berg winds precede Coastal Low Pressures

19. CAUSES OF URBAN HEAT ISLAND

20. EFFECTS OF URBAN HEAT ISLAND
Weather station Model
➢ Increase in air pollution
➢ Increase in greenhouse gasses
➢ Respiratory discomfort. Asthma
➢ Increased precipitation
➢ Reduced insolation (pollution)
➢ Human discomfort
➢ Heat stroke-deaths
➢ Reduced visibility (smog)
➢ Increased energy use
➢ Air conditioners

21. FEATURES ON A SOUTH AFRICAN SYNOPTIC WEATHER MAP