Summary
Grade 11 Geography (entire year summary)
- Course
- Geography
- Institution
- St Stithians College (Stithian)
Summary of grade 11 Geography including: - climatology - geomorphology (South Africa) - development - economic development
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Content preview
GEOGRAPHYATMOSPHERE :
The Earth’s Energy Balance :
- Insolation is absorbed by the crust and the Earth’s surface then heats up the overlying atmosphere
through transfer of sensible heat (conduction and convection), latent heat and the release of long-wave
terrestrial radiation.
- Insolation is received unequally across the Earth’s surface :
1. The Earth’s crust is made of different substances, land and water which heat and cool at
different rates
2. The latitudes are spread across the earth’s spherical shape
3. The Earth rotates on its own axis causing day and night time heating and cooling as well as
creating seasons
4. The earth revolves around the sun causing different parts of the earth to experience different
seasons at a time
5. Cloud cover varies across the earth, higher cloud cover results in more insolation being
reflected back to space and less insolation reaching the surface
- Temperature changes with latitude. It is generally higher near the equator and decreases toward the
poles.
- Temperature changes throughout the year with the change in season.
- In January, the southern hemisphere has summer and is warm, while the northern hemisphere has
winter and is cold. The opposite occurs in July.
- Places in the lower latitudes do not have a large difference in temperature from January to July.
- Places in the higher latitudes have a large difference in temperature from January to July.
Latitudinal Influence :
More surface area to heat up Less direct insolation, rays more oblique
Rays have to pass through more atmosphere
therefore more insolation is lost
Sun
More direct and perpendicular rays
Less surface area to heat up
Less area of atmosphere to pass through
,Seasonal Influence :
1. The Earth’s Axis
- tilted at 23.5 to the North-South pole axis
- it rotates once every 24 hours
- atmospheric temperatures are thus influenced
2. The Revolution Around the Sun
- earth takes 365.5 days to orbit around the sun
- amount of light the planet receives varies
- the angle of the earth’s axis does not change
Therefore the amount (day vs night) and type (direct vs oblique) of insolation changes = seasons
The Radiation Balance :
The Earth’s energy balance describes how the incoming energy from the sun is used and returned to
space.
To achieve a balance between incoming radiation and outgoing radiation on the Earth, the same
amount of radiation that is received must be lost.
Annual Radiation Budget : - Some places receive more insolation than they lose = net radiation
surplus (0-30 N&S)
- Some places receive less radiation than they lose = net radiation
deficit (40-90 N&S)
These differences in the energy gain and energy loss mean there is an energy imbalance in the
radiation budgets at the tropics and the poles.
Winds and Ocean Currents :
1. Vertical Transfer
- radiation
- conduction
- convection
- latent heat release
2. Horizontal Transfer
- surface winds (80%)
- ocean currents (20%)
Ocean Currents : - help the atmosphere distribute the Earth’s uneven insolation
- ocean circulation moves heat that is stored in the water from lower to higher
latitudes
Wind : - uneven heating of the Earth creates pressure differences in the atmosphere
- this difference creates a pressure gradient force and causes wind to blow from regions of high
pressure to low pressure
- a belt of low pressure forms in the equatorial regions
, Global Air Circulation :
LOW PRESSURES (cyclones)
Terrestrial radiation heats up the surface air =
o Air will converge along the surface
o Air is warm, moist and less dense
o Air rises up in a clockwise direction
= low pressure on the surface
Unstable : Cloudy conditions and rain (RCCCR)
HIGH PRESSURES (anticyclones)
Air has risen and lost its heat =
o Air is cool, dry and dense
o It sinks in an anticlockwise direction
o Air will converge along the surface
= high pressure on the surface
Stable : Clear, fine conditions
Pressure Gradient Force :
- Differences in atmospheric pressure cause a pressure gradient (PG) to be set up
- The gradient creates a force causing air to move from a HP to a LP
- The force is stronger when the PG is steeper creating a stronger wind
- Gentle gradients cause a weaker force and weaker wind
- If the only force influencing the winds was PGF than they would flow directly straight
Close isobars = steep PG
Spaced isobars = gentle PG
The Coriolis Force :
- The Earth’s rotation on its axis causes surface winds to deflect off their north/south direction
- The force is not found between 0-5 N&S
- The force strengthens when wind is blowing faster
- Ferrel’s Law dictates the direction air will be deflected in
Northern Hemisphere = deflected to the right
Southern Hemisphere = deflected to the left
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