The Earths Atmosphere

1
The Earths Atmosphere

• Atmosphere envelope of gas surrounding the
  Earth, held to the surface by gravity
• Source of atmosphere volcanic outgassing and
  import via bolides
• Composition 78 N2, 21 O2, lt1 inert gases such
  as argon, neon, and helium
• Other important gases CO2 (0.03, 270ppm), CH4
  (methane), O3
• Also found in atmosphere water vapor, dust,
  pollen

2
Atmospheric Pressure

• Atmospheric gases held aloft by heat energy, held
  to surface by gravity
• Atmosphere densest at surface, thins with
  altitude
• Pressure exerted by atmosphere is barometric
  pressure measured with barometer
• Barometers measure displacement of liquid mercury
  in inches sea level barometric pressure is 30
  inches or 1 bar
• Aneroid barometers work without liquid mercury
  compression of chamber deflects pointer
• Altimeters are barometers scaled to altitude

3
Solar Radiation

• Sun emits electromagnetic energy (EM) in a wide
  variety of wavelengths and frequencies
• Wavelength distance between crests of a wave
• Frequency number of wave crests that pass a
  point in one second
• longer wavelength energy includes radar,
  microwaves, infrared short wavelengths include
  ultraviolet, x-rays, and cosmic rays
• visible light falls between infrared and
  ultraviolet
• all objects absorb and radiate EM, ex heated
  iron bar emits long wavelength energy glows
  red, heated further glows white hot

4
Solar Radiation

• EM is transmitted through vacuum of space without
  energy loss
• EM is transmitted directly through transparent
  objects without energy loss, i.e., light through
  a window or x-rays through skin and muscles
• non-transparent objects reflect some light and
  absorb and re-radiate some
• Earths surface absorbs solar uv EM and
  re-radiates it as longer wavelength infrared
  energy

5
Solar Radiation

• absorption of EM controlled by albedo, the
  proportional reflectance of an object
• mirrors reflect almost 100 of light, all objects
  reflect some light
• snow glaciers have high albedo (80-90 of
  sunlight is reflected), asphalt is low (10-15)
• Oceans have low albedo absorb solar energy and
  affect global radiation balance
• atmospheric particles scatter sunlight in all
  directions, causes the sky to be blue, unlike Moon

6
Radiation Balance

• 50 of the solar radiation striking Earths
  atmosphere is scattered, absorbed, or reflected
• 3 is reflected by the surface, 47 is absorbed
  to be re-radiated as infrared EM (heat)
• this re-radiated heat is trapped within the
  atmosphere, creating a warm, insulating surface
  blanket, this is called the greenhouse effect
• gases that absorb trap EM at surface are
  greenhouse gases most important are water vapor
  and CO2

7
Temperature changes with elevation

• The layer of atmosphere closest to Earth is the
  Troposhere -contains gases, water vapor, weather!
• Troposhere is warm near surface where gases
  absorb EM, cooler where thinner at altitude
• top of Troposhere is called Tropopause (17 km)
  marks boundary into thin, cold Stratosphere
• Stratosphere is very cold up to 35 km at this
  point O2 is broken down into free oxygen by solar
  EM and recombines to form ozone layer (O3) which
  absorbs uv and warms upper Stratosphere
• ozone layer protects life from uv which is
  damaging to living tissue

8
Temperature changes with elevation

• high in the Stratosphere, the ozone layer is
  thinner and temps decline rapidly, at 55 km is
  the boundary called the Stratopause, which marks
  the bottom of the Mesosphere, a layer of
  atmosphere that is extremely thin and cold
• the top of the Mesosphere (80 km) is the
  Mesopause, and marks the beginning of the
  outermost atmospheric layer, the Thermopause,
  which is actually warmer due to the direct
  exposure to high energy solar EM

9
Temp changes with Latitude and Season

• Temperature of the Earths surface varies with
  degree of solar insolation
• variations occur in relation to latitude and
  season
• latitudinal variations occur due to dispersion of
  Suns rays over a greater area due to angle of
  incidence
• seasonal variations are due to the tilt of the
  Earth on its axis (23.5o) No. hemisphere is
  closest to Sun during summer solstice (Jun 21)
  when sun is directly overhead at 23.5oN (Tropic
  of Cancer) no. hemisphere is furthest from the
  sun at winter solstice, when sun is directly
  overhead at 23.5oS (Tropic of Capricorn)
• equinoxes occur when Sun is directly over equator
  and mark beginning of Spring and Autumn (May 21,
  Sep 21)

10
Temperature changes due to heat transport and
storage

• Temperature distribution on the Earths surface
  is not constant with latitude - variations can be
  mapped as isotherms lines of same average temp
• displacement of isotherms from latitudinal lines
  is caused as heat is transported by wind and
  ocean currents, and by dissimilar heat absorption
  levels between land and sea
• heat can be transported by conduction, contact
  between atoms, or convection, transport of heat
  via currents in fluids (air water)

11
Temperature changes due to heat transport and
storage

• Currents in the ocean and atmosphere are the
  primary agents of heat distribution on the
  Earths surface
• vertical flow convection, which creates low
  pressure zones
• horizontal flow advection, caused as air moves
  toward zones of low pressure
• state changes in water affect storage and release
  of heat at the Earths surface latent or stored
  heat is released as water freezes or condenses,
  this heat is released as water melts or
  evaporates
• water absorbs and releases heat slower than land,
  thus proximity to oceans moderates heat
  fluctuations on the Earths surface