Download - The Ozone ‘Hole’
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The Ozone ‘Hole’
The Heat Balance
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What is the purpose of ozone?
• Located in stratosphere 25-30km a.s.l.• Acts as protective shield against ultra-
violet (UV) radiation from the sun
What damage can UV radiation cause?
- Sunburn – skin cancer – snow blindness – cataracts – eye damage – ageing of skin – wrinkling of skin – 1997 suggested link to blood cancer
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What is the ozone ‘hole’?• Depletion 1st observed by British Antarctic
Survey in 1977
• First ‘hole’ noted in 1985
• There is no actual hole in the layer of gases, they have just been depleted by over 50%
• Each spring (Sept-Nov) over Antarctic the very low temperatures cause ozone to be destroyed in chemical reaction with chlorine
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Where does the chlorine come from?
• Chloroflorocarbons – aerosols, refridgerator coolant, manufacture of foam packaging (long term)
• Major volcanic eruptions – (short term)
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How bad is the problem?
• 1993 Antarctic - over an area the size of the USA ozone was reduced to between half or two thirds of its 1970 levels
• Over the Arctic ozone ‘hole’ first notes in 1989, ozone decreased 10% in 1990s
• In Britain increase in UV rays 6.8% per decade since 1979
• 1% less ozone = 5% increase in skin cancer
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Can ozone appear else where?
• Car exhausts generate ozone close to the earth’s surface
• Damages plants & causes health problems eg. asthma (London 1994, Paris 1995)
• Ground level ozone increases during warm, sunny, anticyclonic conditions
• Nitrogen oxides from exhausts can react with Volatile Organic Compounds (VOCs) in sunlight to produce petrochemical smog under extreme conditions
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How is the troposphere heated?• The earth’s atmosphere is not directly heated by the
sun.• The rays from the sun are mainly short-wave light rays
(insolation).• SW rays are absorbed by the earth’s surface,
converted into heat and returned to the atmosphere as long-wave heat rays by:
a) Radiation – transfer of heat by electromagnetic wavesb) Conduction – transfer by contact eg. poker in a firec) Convection – mass movement of a gas or liquid
These LW heat rays are trapped by the water vapour in the atmosphere – this is called the Greenhouse Effect.
Therefore, the atmosphere is heated from below and temperature decreases with altitude in the troposphere
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The Heat Budget• The earth’s temp. remains
fairly constant • Due to balance between SW
(incoming) and LW outgoing radiation
• Net gain every where on earth’s surface except polar areas (high latitude & albedo) – curve A
• Net loss throughout atmosphere – curve B
• Net surplus between 35OS – 40ON (positive heat balance)
• Net deficit at high latitudes (polar regions) and high altitudes
(negative heat balance)
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So how is the heat surplus between 40oN&S transferred to other areas?
2 major heat transfers take place to stop tropical areas overheating.
1.Horizontal Heat Transfers from equator to poles
80% by winds20% by ocean currents
• 2. Vertical Heat Transfers• Conduction• Convection• Radiation• Latent heat – the amount of
heat energy needed to change the state of a substance without affecting its temperature.
• Heat is used up in melting & evaporation
• Heat is released by condensation & freezing (warming the atmosphere)
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Heat Transfers
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Global factors affecting insolation(Long term)
• 1. height above sea level (altitude)
• Why does temp decrease with height?
• Decreased area of land surface from which to heat the air
• Density or pressure of air decreases – air not as able to hold heat (molecules fewer and more widely spaced)
• 2. Altitude of the sun• As move towards pole
land area to be heated by each ray increases due to angle
• & depth of atmosphere to pass through increases (more chance for scattering, absorption, reflection)
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Global factors affecting insolation(Long term)
• 3. Land and sea• Diff. abilities to absorb,
transfer & radiate heat energy
• Sea absorbs heat to 10m depth
• Sea transfers heat to greater depths via waves & currents
• Oceans act as thermal reservoirs in winter
• Sea has greater specific heat capacity
• SHC is the amount of energy required to raise the temp of 1kg of a substance by 1oC
• SHC of water 1 kilocalorie• SHC of land 0.5 kc• SHC of sand 0.2 kc
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Mean annual range in temperature oCCoastal areas have a smaller annual range of temp. than locations at
centre of continents
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Global factors affecting insolation(Long term)
• 4. prevailing winds• Temp determined by area of origin and the surface over
which it has blown
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Global factors affecting insolation(Long term)
• 5. ocean currents• Horizontal transfer of heat energy• Warm currents head towards poles• Cold currents from poles to equator
Circular currents:
Clockwise in N
Anticlockwise in S
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Temperature Anomaly = this term is used to describe temperature differences from a meanEg. Stornoway has a mean Jan temp 20oC higher than the aver for other places at 58oNNE Siberia 24oC colder than the mean at its latitude. WHY?
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Controls on temperature at global level:
• Latitude – angle of the sun
• Revolution – earth revolves around the sun in 365 and a quarter days
• Rotation – earth takes 24 hours to rotate on its own axis
• Tilt – earth is tilted at 66.5o to the horizontal path of the earth’s travel
Seasonal changes:
• Solstices – June 21st is the summer (sun at 54o and 17.5 hrs sunlight) – winter is December 22nd (sun at 12o and 6.5 hrs sunlight)
• Equinoxes – March 21st & September 22nd – sun overhead at the equator and all places have equal day and night
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Local influences on insolation
• Aspect • Cloud cover- Clouds reduce day time temps- Provide insulating layer to
retain heat at night- World’s greatest diurnal temp
range found in tropical deserts
• Urbanisation- Affects the albedo- Creates urban ‘heat islands’
South facing - ubac
North facing - adret