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Summary Geography grade 11 notes
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ClimatologyChapter 1: Earths Energy Balance
Unit 1
Unequal heating of the atmosphere- latitudinal and seasonal
Temperature of atmosphere changes with seasons
o Seasonal changes in temperature tell us that there is unequal heating in the atmosphere
Temperature changes with latitude
o Highest near the equator
o Lowest near the poles
o Shows the atmosphere is unequally heated lattitudinally as well
Isotherm maps
o Show pattern of world temperatures
o Show heating of the atmosphere
o Isotherms: lines joining places of equal temperature
o Heat equator is an isotherm
Joining places that have the highest temperature at a particular time
o Show that
Temperatures change with latitude. Temperatures are generally highest near the equator, decreased
towards the poles
Temperature changes during the year, with the seasons
In January the southern hemisphere has summer and is hotter, while northern hemisphere has
winter and is cooler
In July the southern hemisphere has winter and is colder, while the northern hemisphere has
summer and is warmer
Places within about 20° North and south of the equator do not have marked temperature
differences from January to July- they have high temps all year
Heat equator shifts during the year. South in January and north in July
Unit 2
The significance of Earth’s axis and revolution around the sun
Radiation: transfer of energy by means of waves
Solar radiation: radiation from the sun
Terrestrial radiation: radiation from earth
1. Review processes that heat the atmosphere:
Source of energy for earth is the sun
Sun’s energy is transferred by waves- called radiation
Wavelength of radiation is related to the temperature of the radiating body
o Sun is a very hot radiating body- so its radiation will be shot length
Earth transfers its heat to the atmosphere in 4 ways:
o Radiation- earth is much cooler than the sun, so its radiation (terrestrial radiation) has a longer wavelength.
The atmosphere is better able to absorb this, so it is effectively warmed by it
o Convection- the transfer of heat as hot air near the surface expands and rises
o Conduction- the transfer of heat upwards by molecules of gas and dust in contact with each other
o Release of latent heat: by water vapor when it condenses in the atmosphere. Also known as hidden heat
2. Factors that affect the amount of solar radiation received at the Earth’s surface
Heat transferred from the surface of the earth is the main source of heat for the atmosphere
The more solar radiation earth’s surface received, the more it’s heated and therefore the atmosphere is heated
Two most important factors that affect how much solar radiation earth’s surface receives:
o Length of day and night: earth only received radiation from the sun during the day. (Longer the day, more
radiation will receive)
o The angle at which the sun’s rays strike the earth
Direct rays- heat is concentrated over a small area, travels through less atmosphere= higher
temperatures
Indirect rays- heat is distributed over a larger area, travels through more atmosphere = lower
temperatures
T.Hockly
,3. Earths revolution around the sun on its axis
Southern hemisphere
21 March- autumn equinox
o Neither hemisphere is tilted towards the sun
o Day is equal to night
o Noon angle of the sun is 90° at the equator, and lower everywhere else
21 June- Winter solstice
o Northern hemisphere is tilted towards the sun
o Day is shorter than the night
o Noon angle of the sun is 90° at the tropic of cancer, and lower everywhere else
21 September- Spring equinox
o Neither hemisphere is tilted towards the sun
o Day is equal to night
o Non angle of the sun is 90° at the equator, and lower everywhere else
21 December- Summer solstice
o Southern hemisphere is tilted towards the sun
o Night is shorter than the day
o Noon angle of the sun is 90° at the tropic of Capricorn, and lower everywhere else
Solstices- when one hemisphere is tilted toward the sun and has summer, while the other hemisphere is tilted away
from the sun and has winter
Equinoxes- when neither hemisphere is tilted towards or away from the sun
Parallelism of the axis- the constant alignment of the earth’s axis as it revolves
Unit 3
Transfer of energy and energy balance- role of ocean currents and winds
1. The energy balance for the whole earth
Earths energy balance: the balance between incoming solar radiation (INSOLATION) and outgoing long wave
(terrestrial) radiation
2. Latitudinal imbalances in incoming and outgoing radiation
Radiation surplus- more radiation is received than what leaves
Radiation deficit-more radiation leaves than is received
The areas of surplus are low latitudes (equator) and areas of deficit are high latitudes (poles)
The amount of surplus and deficit are equal when looking at the earth as a whole, therefore incoming and outgoing
radiation is balanced for earth as a whole
3. Poleward transfer of energy to bring about a global energy balance:
Low latitudes should be getting hotter and hotter and the high latitudes getting colder but this is not the case
Energy is transferred from paces of surplus to laces of deficit to bring about a global balance
4. Mechanisms responsible for the poleward transfer of energy:
Mechanisms responsible for the transfer of energy
o Winds 80%
o Ocean currents 20%
Importance of energy transfer by ocean currents:
o Without ocean currents, the water in parts of the ocean around Europe would freeze. Shipping and fishing
would be difficult
o Warm and cold currents can make paces more comfortable to live in
o Without energy transfer by wind, world climates would be different and people would be distributed
differently across the world
Energy transfer happens on two levels
o Deep ocean circulation:
Movement of deep ocean currents driven by differences in the density of the water
Colder, saltier water is denser than warmer less salty water
Cold currents are about 4000m below the surface
Warm currents are about 1000m below the surface
o Surface currents:
Flow in the upper 400m of water
Move in circular patterns called gyres- clockwise in NH and anticlockwise in SH
Carry warm water poleward and cold water towards the equator
Energy transfer by winds: wind is the horizontal movement of air
o Carry warm wind poleward and cold wind towards the equator
T.Hockly
,Chapter 2: Global Air circulation
Unit 1:
Global circulation as a response to unequal heating of the atmosphere
Global air circulation- the large scale movement of air across the globe
1. The unicellular model of global circulation:
Earth is not heated equally
At equator there is surplus and at the poles there is a deficit
Equator is hotter than the poles- heat budget
Warm air rises at equator- flows towards poles
Cold air sinks at poles
Buildup of air at poles- excess flows to equator- heated, then rises- flows back to poles
o Completing the convection system
Vertical and horizontal air movement:
Ascend- move upward
Subside- move downward
Converge- move towards the same place
Diverge- move away from one place in different directions
Movement of air happens at two levels
o Close to the surface
o In the upper air
Movement of air happens in two directions
o Vertically (upwards and downwards away from and towards the earth’s surface)
Ascending and subsiding air
Air ascends at equator and subsides at poles
Rising air cools, subsiding air warms
o Horizontally (parallel to earth’s surface)
Horizontal movement of air is wind
Converge and diverge
Equator to pole- upper atmosphere
Pole to equator- closer to surface of earth
o Horizontal and vertical movement of air are linked
When air subsides from above, it must spread out (diverge) or it would pile up
When surface air converges, it must rise up
In upper air, ascending air must diverge
These movements of air have an impact of weather
Rising air cools leading to cloud and rain formation
Descending air warms- dry conditions
Unit 2
World pressure patterns
1. Atmospheric pressure
Atmospheric pressure- the force per unit area exerted against a surface by the weight of a column of air above that
surface/ the force exerted by the weight of the atmosphere on a surface
There is a link between the height of the column of the air and the pressure it exerts on the surface
Pressure is not the same everywhere
o Sea level more pressure
o Higher altitudes less pressure
2. Reasons for horizontal variations in pressure
The relationship between temperature and pressure
Warm air exerts less pressure than the cooler air
o Warm air expands. Molecules of gas spread out and density decreases. The warm air will have less weight and
lower pressure
o Cold air contracts. Molecules of gas are packed closely together and density increases. The air will have more
weight and pressure will be high
The relationship between vertical air movement and pressure:
Where air rises above a surface, the surface pressure at the surface will be low
Where air subsides over a surface, the surface pressure at the surface will be high
The weight of the upper layers of the atmosphere compress the lower layers of the atmosphere
T.Hockly
, Factors that influence pressure across the earth’s surface:
Altitude:
o Pressure decreases with an increase in altitude
o Places close to the sea level have higher pressures
Water vapour
o Water vapour weighs less than dry air at the same temperature
o Air with high water content will be less dense and therefore rise
Temperature
o High temperatures cause air to expand and become less dense- and rise
o Cold temperature cause air to contract and become dense- and sink
Air movement
o Convergence of air causes it to rise and so a low pressure is found
o Divergence of air causes air to subside/sink and so a high pressure is found
Position over land/sea
o In summer lad masses are hot and a low pressure forms
o In w inter land masses are cold and a high pressure forms
Causes of pressure:
Thermal
o Low of high pressure caused by the temperature of air
Dynamic
o Low or high pressure caused by the movement of air
3. World pressure belts
Pressure is arranged in belts of high and low pressure
The pattern is the same in each hemisphere
Pressure belts are all associated with the latitudinal differences I’m temperature, and with patterns of ascending
and subsiding air
Equatorial lows 0
o Caused by warm air rising at the ITCZ (inter tropical convergence zone)
o Clouds and rain form in this region because of moist air rising, cooling and condensing
o The ITCZ shifts moth and south of the equator
o The ITCZ is not straight and parallel to the lines of latitude (there are bends and waves that occur due to
different heating characteristics of land and water)
Subtropical high pressure 30
o Air in upper atmosphere cools and sinks in the tropics causing areas of high pressure
o It causes clear skies and low rainfall with warm, dry conditions
o South Africa is in this belt
Sub polar low pressure 60 N/S
o Occurs where warm subtropical and cold polar air masses at the sub-polar low cause frontal uplift
o Mid latitude cyclones are formed here, at the polar front
Polar high 90
o Associated with cold, dense, sinking air
Unit 3
The tri-cellular model of global circulation: Hadley, Ferrel and Polar cells
Tri-cellular model of global air circulation- model of global air circulation featuring three cells of circulation in each
hemisphere
Intertropical convergence zone (ITCZ) - area where winds from the two cells converge, between the two Hadley cells of
the tri-cellular model of global air circulation.
Air mass- very large volume of air with particular characteristics
Front- the boundary between air masses that have different characteristics
Each cell has 4 components
o Two of horizontal movement
o Two of vertical movement
As air moves in these cells, it transports warm air poleward and cold air equator-ward
Doldrums: 0°-5°- no wind
T.Hockly
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