Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
Hwa Chong Institution (High School)
Term 1 - 2010
Sec 4 Geography
Revision Notes
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Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
Content page
Lighthouse of this note
Section I: Terms and conditions
Section A: Atmosphere, Weather and Climate
Section B: Elements of weather and climate
Section C: Humidity and precipitation
Section D: Planetary Wind and pressure
TERM AND CONDITIONS
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Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
Section A: Atmosphere, Weather and Climate
The more original a discovery, the more obvious it seems afterwards.
STRUCTURE OF EARTH’S ATMOSPHERE
� Atmosphere
� An envelope of transparent, odorless gases
� It is held in place by the pull of Earth’s gravitational forces
� Earth’s gravity is strongest nearer to the surface, therefore, most of the atmosphere is
found near the surface.
� Consists mostly of:
� Nitrogen (78%)
� Oxygen (21%)
� Water vapor
� Dust particles
STRUCTURE AND COMPOSITION OF ATMOSPHERE
� Using temperature, atmosphere can be divided into 4 distinct layers:
1. Troposphere
2. Stratosphere
3. Mesosphere
4. Thermosphere
TROPOSPHERE
� Approximately 0 to 14 km above sea level
� Temperature decreases by 6.4 degrees for every 1000m increase in altitude
� Temp is due to solar radiation which keeps earth warm
� Falls in pressure due to the decreasing effect of gravity
� The most unstable layer
� Topped by an isothermal layer
STRATOSPHERE
� Steady rise in temp caused by ozone
� Pressure continues to fall
� Dry air; little or no weather
� Acts as a protective shield against meteorite which usually burns out as it enters earth’s
gravitational field
MESOSPHERE
� Temperature falls rapidly due to no water vapor, cloud or dust or ozone to absorb incoming
radiation
� Lowest temperature – 90 degrees
� Strongest winds – 3000km/hr
THERMOSPHERE
� Temperature rise rapidly with height to reach 1500 degrees
� Due to atomic oxygen which has the same function as ozone.
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
ENERGY IN THE ATMOSPHERE
� 3 ways in which solar radiation is treated by atmosphere:
� Absorption: mainly my ozone, dust, water vapour and carbon dioxide, greenhouse
gases
� Reflection: reflection radiation back into space
� Scattering: Incoming radiation is diverted by molecules of gas and becomes diffused
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
IMPORTANCE OF THE ATMOSPHERE
� Helps sustain life
� Protects the Earth
WEATHER VS CLIMATE
� Weather
� When this happens, we experience a change
in weather
� Meteorologists define ‘weather’ as the condition
of the atmosphere at a particular place over a short period of time
� Climate
� Weather pattern of a place over a long period of time, usually 30 years
� The basic elements of weather and climate:
� Sunshine
� Temperature
� Humidity
� Clouds
� Rainfall
� Air pressure
� Wind
HOW WEATHER AND CLIMATE AFFECT PEOPLE
� Weather affects our daily life
� Climate affects how people live generally
� Where people choose to live
� Types of houses people live in
� Climate affects food and water supply
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
Section B: Elements of Weather climate
We have, I fear, confused power with greatness.
DEFINITION OF TEMPERATURE
� Temperature is the degree of heat or cold in the atmosphere
� It is measured in ºC or ºF
WARMING OF AIR
Convection Hot air, being lighter than cold air, rises as a
convection current
Conduction Air receives heat from the ground it is in
contact with
Radiation Heat energy from the ground is sent back to
space. This form of heat energy can travel in a
vacuum
Factor
influencing
Temperature
Description
Latitude � Places near the Equator are hotter than places near the poles due to
the angle at which sun’s ray strike the Earth
� Amount of heat received by Earth’s surfaces decreases with latitude
due to the decreasing angle of incidence Angle at which sun’s ray hits
earth of the sun’s ray
� Earth’s axis is tilted at an angle of 23.5º from the vertical
� From June to Aug, there is a higher intensity of the sun’s ray in the
northern hemisphere
� The higher latitudes in the northern hemisphere experience higher
temperature in summer while the higher latitudes in the southern
hemisphere experience low temp in winter.
Altitude � Temperature falls by 6.4ºC for every 1000m increase in height.
� This fall in temperature is called the normal lapse rate.
� Air is warmed by the heat radiated from the ground due to conduction
and convection. It is much warmer as there is larger land
� Most of Earth's surface gases are also concentrated at the Earth’s
surface.
� Temperature sometimes rise with altitude in the troposphere due to:
� Rapid outgoing terrestrial radiation on a cloudless night.
� Cold air rolling down slope displacing the Warmer air
� Warm air rises over cold air at a warm front
� Cold air undercutting warm air at a cold front
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
Distance from
the sea
� Sea heats up and loses heat more slowly than land
� Coastal area temperature is influenced.
� In temperate latitudes, coastal areas have a smaller temperature range
between summer and winter
� Inland areas far from the sea are not affected by the ocean thus having
a larger annual temperature range.
Ocean
currents
� Change in temperature is due to ocean currents in the area
� Ocean current are set in motion by prevailing winds blowing over the
surface
� 2 types of ocean currents:
� Warm – Originates from equator
� Cold – Originates from higher latitudes
Aspect � Refers to the direction of the slope of the land relative to the sun
� More obvious in temperate regions rather than tropical regions
� In northern hemisphere, south facing slope have higher temp than
north facing slope
Humidity � Humidity is the state of the atmosphere with respect to its amount of
water vapour
� The higher the humidity, the more clouds there will be as clouds are
formed by condensation of water vapour.
� Thick cloud cover prevents solar radiation from entering in the day and
outgoing terrestrial radiation escaping in the night.
� Therefore, equatorial areas which have high humidity and thick cloud
cover have low diurnal temp range.
Land surface � An area with vegetation is much cooler than an area of concrete.
� Vegetation reduces the incoming radiation and prevents absorption of
heat into the ground.
� Concrete surfaces absorb heat quickly in the day and releases heat
lowly at night.
SIX’S THERMOMETER
� Maximum temperature is measured by the maximum thermometer
� It consists of a glass tube containing mercury and a metal index
� When temperature rises, the mercury expands and pushes the metal index upwards
� When temperature falls and the mercury contracts,
the metal index stays in place
� The minimum thermometer works in the same way, but contains alcohol instead of mercury.
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
Section C: Humidity and precipitation
The shortest distance between two points is always under construction.
HUMIDITY
� The state of atmosphere with respect to its water vapor content
� Warm air can hold more water vapour than cold air
� Water vapour comes from the evaporation of water from ponds, lakes, rivers, seas and
oceans.
� Saturation point is reached when air contains all the water vapour it is able to hold at a
particular temperature
RELATIVE HUMIDITY
� The ratio of the actual amount of water vapour in the air at a particular temperature to the
maximum quantity of water vapor the air can hold at that temperature
� Usually measured as a %
SATURATION POINT
� when the air reaches the maximum capacity to hold water vapor
DEW POINT TEMPERATURE
� The temperature at which Saturation Point is reached;
Name of the cloud Description
Cirrus
Thin and wispy
Cumulus
Round and wooly
Stratus
Flattish low clouds,
occurs in layers
Cumulonimbus Huge, towering
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
TYPE OF PRECIPITATION
Type of
precipitation
Description
Rainfall � The air rises or is lifted
� The air that has risen or has been lifted cools
� The cool air becomes saturated at dew point ie, it is holding all the water
vapour it can hold at a particular temp.
� When air is cooled further, it continues to rise, the water vapour in it
condenses into water droplets around atmospheric particles
� The water droplets forms clouds
� When the water droplets in clouds are too heavy to be suspended in air rain
falls
Snow � Forms under similar conditions to rain
� Except that as dew points temperatures are under 0ºC, then water vapour
condenses directly into solid (Sublimation)
Sleet � Is a mixture of ice and snow formed when the upper air temperature is
below freezing, allowing snowflakes to form and lower air temperature is
around 2 to 4ºC which allows them to melt partially
Hail � Made up of frozen raindrops which exceeds 5mm in diameter
� It usually forms in cumulonimbus clouds resulting from the uplift of air by
convection currents or at a cold front.
� More common in summer areas where more heat triggers off the uplifting
of air.
THEORY OF PRECIPITATION
� Minute water droplets (less than 0.05mm in diameter) or ice crystals (if dew point
temperature is below freezing) are produced from condensation
� Very tiny and weigh very little
� Constantly kept buoyant by the same rising air currents that produce them
� Water droplets and ice crystals need to become sufficiently large to overcome this uplift
COLLISION & COALESCENCe
� ‘warm’ clouds (containing no ice crystals) are found in tropics contain numerous water
droplets of differing sizes
� different-sized droplets swept upwards at varying velocities – collide with other droplets
� the larger the droplet, the greater the chance of collision and coalescence with smaller
droplets
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
� when coalescing droplets reach a radius of 3mm, their motion causes them to disintegrate
to form a fresh supply of droplets
� thicker clouds provide more time for droplets to grow, with them falling faster (thundery
showers)
TYPE OF RAINFALL
Type of
rainfall
Description
Convectional � On a hot day, the air in contact with the warm ground is warmed by
conduction.
� The warm air with higher temperature than the surrounding air rises
and is said to be unstable.
� This unstable warm air which holds a lot of moisture rises in a
convection current.
� As it rises to great height, it cools.
� Further cooling after it reaches dew point causes water vapor to
condense into water droplets around particles such as dust and smoke.
� The water droplets form towering cumulonimbus clouds.
� When the water droplets are too heavy to be suspended, conventional
rain falls.
Relief � Orographic rain occurs when near-saturated, warm maritime air is
forced to rise when confronted by a coastal mountain barrier.
� As air rises, it cools.
� Air becomes saturated when dew point is reached at the level of
condensation.
� Condensation occurs upon further cooling, forming water droplets that
coalesce to form clouds.
� When the water droplets become too heavy, they fall as relief rain on
the windward slop.
� The leeward side of the mountain forms a rain shadow area.
� After crossing the mountain, descending dry air is warmer.
� Forms warm dry wind on the leeward slope and it brings very little
moisture
Frontal � Lighter warm air rises gently over heavier cold air which remains close
to the ground.
� Warm air rises, cools and water vapor condenses to form low to
mid-level clouds like nimbostratus/altocumulus clouds.
� Light rain over wide area for several hours
� Heavy cold air slips under lighter warm air.
� Warm air rises aggressively.
� Cumulonimbus clouds form with heavy rain over a small area with a
short duration.
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
Section D: Planetary pressure system
Life being what it is, one dreams of revenge.
WINDS
� moving air- caused by difference in air pressure
� Wind always moves from area of high pressure to area of low pressure
� Air pressure is measured using a mercury barometer
PLANETARY PRESSURE SYSTEM
1. Equatorial low pressure belt/doldrums (from 5°N to 5°S)
2. Polar high pressure belts (around 90°N to 90°S)
3. Sub-tropical high pressure belts/horse latitudes (around 30°N to 30°S)
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
4. Sub-polar low pressure belts (around 60°N to 60°S)
CORIOLIS
� Due to rotation of the earth and the unequal distribution of land and sea surfaces, winds do
not blow directly from areas of high pressure to low pressure.
� Moving air appears to be deflected to the right in the northern hemisphere and left in the
southern hemisphere.
MAJOR PLANETARY WINDS
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
� Trade winds (Both northeast and southeast)
� Blow from sub-tropical high pressure belts (horse latitudes) to the equatorial
low-pressure belt (doldrum).
� Zone of convergence: ITCZ
� Westerlies
� Blow from sub-tropical high pressure belts to sub-polar low pressure belts.
� Generally warm and dry
� Easterlies
� Blow from polar high-pressure belts to sub-polar low pressure belts.
MONSOON IN SEA & HURRICANE KATRINA
� Regional winds which influence the climate of huge land masses. They are seasonal by
nature and are caused by changes in pressure during the changing seasons between
summer and winter
LOCAL WIND
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes
Prepared by Cao Yu 2010 ©Copyright Reserved 2010/2/19 Last Edited
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