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ASSC 239 Meteorology Spring, 2007

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Title: ASSC 239 Meteorology Spring, 2007


1
ASSC 239MeteorologySpring, 2007
  • Part 1. Energy and Mass
  • Chapter 1.
  • Composition and Structure of the Atmosphere

2
Introduction
  • The Atmosphere
  • Mixture of gas molecules, microscopically small
    suspended particles of solid and liquid, and
    falling precipitation
  • Nitrogen 78 , Oxygen 21 , all other gasses
    about 1
  • Permanent gases (N2 O2) very little with time
    whereas variable gases such as water and CO2
    change with time and location
  • Meteorology
  • Study of the atmosphere and processes that cause
    what we refer to as weather

3
The Thickness of the Atmosphere
  • The atmosphere is held in place by gravity
  • Density decreases rapidly with height. Top of
    atmosphere undefined
  • Majority of mass contained in thin layer near the
    surface (compared to the earth it is like the
    skin compared to the apple)
  • Still contains sum of mass (5.14 x 1015 kg)

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6
Water Vapor
  • The most abundant variable gasabout ¼ of 1 on
    average
  • Added or removed from atmosphere through
    evaporation and condensation in the hydrologic
    cycleresidence time only about 10 days
  • Concentrations exist from nearly 0 over desert
    and polar regions to nearly 4 near tropics
  • Major contributor to Earths energy balance and
    most important atmospheric processes

7
Carbon Dioxide
  • A widely distributed trace gas accounting for
    only 0.036 of total atmospheric mass
  • Important as a greenhouse gas to Earths energy
    balance
  • Added through biologic respiration, volcanic
    activity, decay, and natural and human-related
    combustion removed through photosynthesis

The steady increase of atmospheric CO2 due to
human activities. Seasonal variation related
to rates of photosynthesis, respiration, and
organic decay.
8
Ozone
  • Tri-atomic form of oxygen
  • Near the surface, a pollutant.
  • In the stratosphere, an essential absorber of
    ultraviolet radiation
  • Formed when atomic oxygen (O) bonds with O2
  • Chlorofluorocarbons (CFCs) react with O3 in
    stratosphere. Produces chlorine monoxide.
  • Chlorine unaffected but oxygen is affected
    thereby destroying ozone.

9
Methane
  • Variable gas in small but increasing
    concentrations
  • Released through fossil fuel activities,
    livestock digestion, and agriculture cultivation
    (esp. rice)
  • Very effective absorber of terrestrial radiation.
    Plays an active role in near surface warming

Annual increases in atmospheric methane
10
Aerosols
  • Solid or liquid particle, other than water, which
    exists in atmosphere
  • Synonymous with particulate
  • Both natural (sea spray, dust, combustion) and
    human (combustion) products
  • Easily remain in suspension for long periods
  • Contribute to precipitation and cloud formation
    processes as condensation nuclei
  • Removed by the process of precipitation

11
Density
  • Mass (kg) per unit volume (m3)
  • Due to compressibility, near surface air is more
    dense than that above
  • May be expressed in terms of the mean free path,
    or average distance a molecule travels before
    colliding with another molecule.

12
Due to compressibility, atmospheric
mass gradually thins out with height
13
Thermal Layers of the Atmosphere
  • Four layers of atmosphere emerge from temperature
    characteristics with height

14
Troposphere
  • Lowest layer, promotes atmospheric overturning
  • Layer of virtually all weather processes, steady
    temperature decrease with height
  • decrease 6.5oC/km (3.6oF/1000ft)
  • Thinnest layer but contains 80 of mass of
    atmosphere

15
Troposphere
  • Due to thermal expansion it is thicker (10 mi)
    over the tropics) and only 1/2 that (5 mi) at the
    poles
  • Temperature profile implies atmosphere
    transparent to solar radiation and heated from
    terrestrial radiation absorption or from bottom
    up
  • When the temperature profile is reversed
    (temperature inversion) the warm air acts as a
    lid and holds pollutants near the surface

16
Most clouds exist in the troposphere.
Occasionally, violent updrafts push cloud tops
into the stratosphere. The flattened top of this
cumulonimbus cloud is in the stratosphere.
17
The Stratosphere
  • Area of little weather
  • Layer of inverted temperature after an initial
    layer of constant temperature with height
  • Warms with height to the freezing point of water
    near stratopause
  • Inversion caused by the absorption of ultraviolet
    radiation by ozone
  • Ozone layer exists through an altitude between
    12-18 mi, actual concentration of ozone as low as
    10 ppm

18
The Stratosphere
  • The stratosphere has low moisture content which
    inhibits precipitation
  • Aerosols are trapped in this layer and
    distributed globally by strong winds
  • After the eruption of Mt Pinatubo in 1991, the
    Northern Hemisphere experienced spectacular
    sunsets for months

19
Mesosphere and Thermosphere
  • Combined, two layers account for only 0.1 of
    total atmospheric mass
  • Mesosphere, extends to about 50 mi characterized
    by decreasing temperatures, coldest atmospheric
    layer
  • Thermosphere slowly merges with space,
    characterized by increasing temperatures
  • Temperatures approach 1500oC, however, only
    measures molecular kinetic energy, sparse amount
    of mass precludes actual heat content

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21
The Ionosphere
  • Located within the meso- and thermospheres,
    replete with ions, electrically charged
    particles
  • Subdivided into the D-, E-, and F-layers
  • D and E layers diminish at night allowing the F
    layer to reflect radio waves Interactions between
    the ionosphere and subatomic particles emitted
    from the Sun cause the aurora borealis (northern
    lights) and the aurora australis (southern
    lights)

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23
ROTATION OF EARTH
  • SPEED--once/24 hr, 15o/hr, 1040 mph at the
    equator
  • DIRECTION--W. to E, counter-clock.
  • INCLINATION--23 1/2o of axis
  • RESULTS--day and night

24
REVOLUTION OF THE EARTH
  • DIRECTION--Counter-clockwise
  • SPEED--66,600 mph, 1 revolution/yr
  • PATH--elliptical
  • Closest to the sun in January
  • Farthest from the sun in July
  • Energy varies inversely with the square of the
    distance from the sun

25
SEASONS
  • CAUSES
  • Inclination of the Earth's axis
  • Parallelism of suns rays and axis orientation
  • Revolution of the Earth around the sun
  • SUMMER SOLSTICE, 1st day sum.
  • June 21, longest day of the year (here)
  • Sun over the tropic of cancer
  • WINTER SOLSTICE, 1st day winter
  • December 22, shortest day of the year
  • Sun over the tropic of Capricorn

26
SEASONS
  • EQUINOXES
  • VERNAL
  • March 21, 12 hours sunrise to sun set
  • Sun over the equator, 1st day of spring
  • AUTUMNAL
  • September 21, 1st day of fall
  • Sun over equator, 12 hour day
  • Above the artic circle the sun is either always
    up or always down

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