Introduction to the Atmosphere

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Introduction to the Atmosphere

• Structure of the Atmosphere
• Radiation Budget
• Incoming Solar Radiation
• 6 Factor Day and 4 Factor Night
• www.wyckoffschools.org/.../earthatmosphere.htm

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What is the Atmosphere?

• The Atmosphere
• The Gasses
• The Liquids
• The Solids

• A layer of gasses, liquids and solids that is
  held around the Earth by gravity.
• Nitrogen 78, Oxygen 20.95, Water vapour, Argon,
  CO2 0.03, other as traces
• Water as droplets and polluted versions such as
  acid rain
• Ice, Dust, Pollen, Soot,

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The Different Layers of the Atmosphere

• Troposphere, 1st layer contains 70 of the air,
  including all Greenhouse gasses (Global W
• Tropopause has a temperature throughout of -52oC
• Stratophere, 2nd layer is home to Ozone layer and
  its holes

• www.wyckoffschools.org/.../earthatmosphere.htm
• Each layer is called a sphere
• The boundary are called pause, due to a pause in
  temperature change

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What does the atmosphere do for us?

• Allows us to live
• Provides oxygen for human respiration
• Provide CO2 for plant photosynthesis
• Provides the carbon from which Earths life forms
  are made
• Protects us (Ozone layer cuts out ultraviolet
  rays)
• Keeps us warm (The Greenhouse effect is a good
  thing)
• A place to dump our gas waste and toxic fumes
  (resulting in Acid rain)

• Distributes fresh water
• Spreads the suns heat energy away from the
  equator
• Gives us wind to power transport and electricity
  generation
• Gives us snow for skiing other leisure
  activities
• Makes places more suitable for holidays
• Produces destructive but impressive phenomena
  like Hurricanes
• Gives us something to talk about

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        Source NASA
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What is the Radiation (Energy) Budget

• In theory, all the Earths energy comes from the
  Sun. (Geothermal and tidal power makes a
  negligible contribution, so is left out of Budget
  calculations)
• As energy is neither created nor destroyed, all
  the energy that arrives in the Atmosphere must
  also leave, to maintain an equilibrium ie
  Balanced Budget
• If the balance is not achieved we experience
  Climate Change. Either cooling ie Ice Age or
  Global Warming
• The energy in the Atmosphere can be looked at as
  a system, with Inputs, Output and Processes

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How is the Atmosphere a System?

• Incoming Solar Radiation Insolation Shortwave
  radiation that is emitted from the sun and
  reaches the Earth as light, the suns rays /
  sunshine
• Reflected insolation (albedo)
• Terrestrial radiation Longwave radiation
  emitted from the Earths surface and particles in
  the atmosphere (clouds, dust etc) after the
  shortwave insolation has been absorbed

• Inputs
• Outputs

Mean annual Insolation at the top of Atmosphere
Mean annual Insolation at the Earths surface
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What affects how much Insolation reaches the top
of the Atmosphere?

• Solar Constant
• Orbit of the Earth

• Although relatively constant, varies slightly due
  to Sunspot activity
• The elliptical orbit of the Earth around the Sun
  varies. This cause a 6 variation between the
  most stretch (least radiation) and the roundest
  (most radiation) orbits

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What happens to the Insolation in the Atmosphere?
(The processes)

• Absorption (Input)
• Reflection (Output)
• Emission (Output)
• Scattering (Both)

• Energy is taken in by molecules, causing them to
  move more vigorously, resulting in a rise in
  temperature and/or expansion
• Energy is bounced off surfaces and back out of
  the Atmosphere
• Absorbed energy is given out as longwave
  radiation as particles cool
• Insolation is diverted in different directions by
  particles in the Atmosphere, some of which
  reaches the Earth as Diffuse Radiation

Absorption
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How does the Energy Budget Balance?
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Is Reflection or Emission more significant?

• The average albedo of the Earth is about 0.3,
  which means that 30 of the solar energy is
  reflected back to space, while 70 is absorbed by
  Earth then emitted later. The planet's albedo
  varies spatially ice sheets have a high albedo,
  while oceans, rainforest and tarmac are low.
• So 30 of the incident energy is reflected,
  consisting of
• 6 reflected from the atmosphere
• 20 reflected from clouds
• 4 reflected from the ground (including land,
  water and ice)
• The remaining 70 of the incident energy is
  absorbed
• 51 absorbed by land and water, then emerging in
  the following ways
• 23 transferred back into the atmosphere as
  latent heat by the evaporation of water 7
  transferred back into the atmosphere by heated
  rising air sensible heat 6 radiated directly
  into space 15 transferred into the atmosphere by
  terrestrial radiation, then emitted (reradiated)
  into space
• 19 absorbed by the atmosphere and clouds,
  including
• 16 emitted back to space - 3 transferred to
  clouds, then emitted back to space
• When the Earth is at thermal equilibrium, the
  same 70 that is absorbed is emitted 64 by the
  clouds and atmosphere and 6 by the ground

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When does the Atmosphere Heat and Cool?

• Only during Daylight hours does the Earth receive
  Insolation resulting in heating
• Daylight hours varies across the Earth according
  to latitude and seasonally due to the Earths
  orbit of the Sun
• The apparent movement of the sun overhead
  occurs during the year due to the tilt of the
  Earths axis

• At night time the majority of the energy is
  emitted as Terrestrial (Longwave) radiation
• This will also vary with latitude and time
  throughout the year
• To understand these variations we think about
  Surpluses and Deficits of (radiation) energy

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6 Factor Day Model of Energy Input

• Latent heat transfer during evaporation stores
  energy
• Sensible heat transfer (air, water vapour and
  dust, warm without changing state and move energy
  from the Earth to atmosphere)
• Incoming Solar Radiation (Insolation) absorbed by
  particles in the air (water vapour, CO2, dust)
  add energy
• Reflected Solar Radiation (Diffuse radiation)
• Absorbed energy into the surface and subsurface
  warm atmosphere through conduction and convection
  
• Terrestrial radiation (Longwave earth radiation)
  adds energy to the atmosphere as it travels
  through towards space)

• Mnemonic
• Love SITRA
• Remember, energy is being lost to space all day
  but not as much as arrives

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4 Factor Night Model of Energy Output

• Latent heat given out at dew formation
  (condensation) is released back to space or into
  Earth
• Absorbed energy in the atmosphere is reradiated
  to space or returned to Earth as it cools quicker
  due to rapid heat loss (heat capacity) in the
  form radiation emission
• Sensible heat transfer, warm air and vapour, with
  out changing state transfer heat towards Earth
  cooling the upper atmosphere (convection and
  conduction)
• Terrestrial radiation (Longwave radiation)
  emitted by the Earth as has relatively more than
  the atmosphere and Space around it.

• Mnemonic
• LAST
• Not all energy is lost or we would reach absolute
  zero!

• Terrestrial radiation intensity, from clouds,
  atmosphere and ground

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The Energy (Heat) Budget

• Energy (heat) distribution at Earth
• Energy (heat) Surplus and Deficit
• Vertical and horizontal Heat transfers
• Causes of Temperature Anomalies

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What affects the amount of Energy at different
Latitude?

• Length of Day and Night and Seasonal variation
• Height of the Sun in the Sky (CAT)
• Albedo ( of radiation reflected)

• Due to tilt of axis during orbit different
  amounts of insolation are received.
• Concentration of the suns rays, Angle of
  incident, Thickness of atmosphere
• This will compound the effects of CAT increases
  at the poles due to angle of incidence

Albedo
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Where has a Surplus and Deficit on the Energy
Budget

• Surplus
• Deficit
• Result

• Within the tropics
• North and south of the tropics
• Heat transfers towards space and the poles, this
  helps stop a continuous temperature rise within
  the tropics and continuous fall outside of them

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Major Global Heat Transfers

• Vertical
• Heat is transferred up through the Atmosphere by
  Radiation (Terrestrial Longwave), Convection
  (Thermals), Conduction and as Latent heat (water
  vapour).

• Horizontal
• Winds prevailing surface winds, upper atmosphere
  winds, Jet streams, Rossby Waves and weather
  systems such as Hurricane and Depressions
• Ocean currents at the surface and deep in the
  oceans eg Thermohaline Conveyor

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What leads to Temperature Anomalies at different
Latitudes? Global Scale Regional Scale

• Prevailing Winds
• Ocean currents
• Altitude
• Land and Sea
• Distance from the sea

• Warm winds from the Equatorial region carry
  energy towards the poles
• Warm surface currents transfer energy to the air
  above them, so influencing climatic conditions
• Higher areas eg Himalayan Plateau have cooler
  temperatures due to a low density of air so
  limited amounts of air particles absorbing
  energy. Also there is less land area to heat the
  air with Terrestrial radiation.
• Sea absorbs heat to a great depth (10m) and has a
  higher heat capacity, so takes longer to heat up
  but will emitted radiation for long
• During the summer coastal areas are cooled and in
  winter they are warmed due to the relative
  difference in energy between the sea and land.
  Continental interiors have great temperature
  range

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Anomalies continued Regional Scale Local Scale

• Frequent Cloud Cover
• Sporadic Cloud Cover
• Aspect
• Urbanisation

• Equatorial cloud belts due to convection and
  mid-latitude cloud belts due to fronts,
  noticeably reduces the insolation due to
  reflection and absorption
• Weather systems and air instability will also
  result in clouds
• In the northern hemisphere the south facing
  slopes (ubac) will receive more insolation,
  whereas the north facing slope (adret) is in
  shadow.
• This generates Urban Heat Islands due to use of
  fuels and bark surfaces with a lower albedo eg
  tarmac

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What is the role of Ocean Currents in Heat
transfers?

• Surface currents are the more significant on the
  atmosphere
• Influence temperature and moisture of maritime
  air masses and coastal areas and major component
  of horizontal heat transfers
• Combined influence with the difference between
  land and sea and prevailing winds considerable in
  generating temperature anomalies
• The North Atlantic Drift, South Westerly winds
  and ocean front location combine to give the UK
  its warm damp British climate.

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Atmospheric Circulation

• Linking Heat, Pressure and Wind
• Global Surface Wind Patterns
• Upper Atmosphere winds
• Local Wind variations

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How is Heat, Pressure and Wind Linked?
As air rises it cools becoming more dense
Convection Currents
As pressure increases temperature rises
Pressure gradients are the difference in pressure
which cause wind. Steeper the gradient stronger
the wind. Gradient shown by spacing of isobars
(like contours)
Heated air becomes less dense and rises. Low
pressure at ground level
Descending air causes High pressure at ground
level
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Heat Transfer and Global Winds

• Due to the Surplus heat at the Equator and
  Deficit at the poles the air rises at the Equator
  and descends at the poles.
• Theoretically this should set up one massive
  convection current in each hemisphere
• However, due to the distance, this is unrealistic
  and 3 convection cells are formed.
• The Tricellular Model was created to explain the
  direction of Prevailing Winds at the surface and
  upper Atmospheric winds such as the Jet streams
  and the Rossby Waves

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The Tri-Cellular Model

• Explains the theoretical wind and air pressure
  distribution pattern

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What forces act on the wind?

• Due to convection currents from high to low
  pressure
• Due to the spinning of the Earth, is most
  significant at the poles weakest at Equator
• Roughness of land slows wind causing deflection
  most by mountains (Ekmans spiral)
• Balance in mid-latitude weather systems so wind
  follows isobars (line that join points of equal
  pressure) and spins

• Pressure gradient force
• Coriolis force
• Friction
• Centripetal centrifugal force

                           In upper part of the
picture, the black object moves in a straight
line. However, the observer, red dot who is
rotating shown by the lower part of the picture,
sees the object as following a curved path.
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Why do the Global Winds blow in different
directions?

• Polar Easterlies
• South Westerlies are Geostrophic winds
• The Trade Winds are Pressure gradient winds

• Coriolis is stronger at poles so the winds are
  deflected further right in Northern hemisphere
• Mid-latitude winds that blow along isobars in the
  upper atmosphere as Pressure Gradient force
  Coriolis.
• At the surface friction works against Coriolis so
  winds are deflected slightly across isobars.
  Therefore filling a depression, anti-clockwise
  and leaving an Anti-cyclone, clockwise in the
  Northern hemisphere
• Pressure gradient gt Coriolis near the Equator so
  Trades are North Easterly in the Northern
  hemisphere

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Jet stream deflection and Rossby Waves

• Rossby Waves
• Usually 4-6 large-scale meanders of the PFJS
• Meanders draw cool polar air south and warm
  tropical air north, transferring heat
• When meander cuts off it forms areas of cool air
  that descend, Anti-cyclones and areas of warm air
  that rise, Depressions

• Jet streams
• Bands of extreme winds, 110 to 370km/h, found in
  upper atmosphere
• Discovered in war by pilots, used to bomb USA

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Rossby Wave and Mid-Latitude Systems

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Why do Wind Pressure patterns vary?

• Tri-cellular model links the pressure belts and
  major winds to latitude to give theoretical
  pattern
• The difference between Land and Sea, Distance
  from the sea, Ocean currents, Orographic barriers
  all cause spatial variations
• Apparent movement of Sun, seasonal changes in
  length of day and night, movement of the ITCZ,
  migration of the jet streams and Rossby waves and
  weather systems will all cause temporal
  variations

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How does the ITCZ cause variations

• Conditions
• Seasonal variations

• Radiation surplus latent heat mean high temps
• Strong convection currents cause rising air which
  result in permanent low pressure, Doldrums (areas
  of calm) and pull in the strong trade winds over
  warm oceans
• High moisture content, humidity and instability,
  create Cumulonimbus and daily convectional
  thunderstorms
• Apparent movement of the sun and presence of land
  and sea means ITCZ varies in thickness as well as
  location
• Evidence of movement include shifts in weather
  belts. The SE Asian Monsoons, presents of
  Savannah grasslands instead of Tropical
  Rainforest, El Nino and resulting droughts in the
  Sahel (Ethiopia) in early 70s and 80s

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What are the Meso-scale Winds?

• The Chinook (Rookies), Fohn (Alps), Berg (SA),
  Samoon (Iran), Zonda (Argentina) are seasonal /
  regional winds caused by pressure variations and
  the difference between adiabatic lapse rates due
  to the presents of mountains and planes.
• In the spring planes heat faster as lower albedo,
  so area of low pressure develops. Mountains with
  the snow and ice stay cool developing a pressure
  gradient.
• Rising air is saturated and therefore cool at the
  SALR (0.5oC/100m). At altitude the moisture is
  released as precipitation so the descending air
  warms at the DALR (1oC/100m) due to lack of
  latent heat.
• The warming of the descending air exaggerates the
  effect of the rain shadow that melts any
  remaining snow and can bring drought in extreme
  cases

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Local Winds

• Sea Breezes

• Valley Winds