Midterm I Review

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Midterm I Review
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Topics we have discussed

• Atmospheric sciences at a glance
• Evolution of the atmosphere
• What cause the four seasons?
• What is the greenhouse effect?
• What set the atmosphere in motion?

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The mission of the atmospheric sciences is to
understand and predict weather, climate, and
related disasters
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Atmospheric sciences at a glance

• Atmosphere A mixture of gas molecules,
  microscopically small particles of solid and
  liquid, and falling precipitation
• Meteorology The study of the atmosphere and the
  processes that form weather
• Weather The state of the atmosphere at a given
  time and place
• Climate The statistical properties of the
  atmosphere. (i.e. averages and variability)
• Weather- and climate-related disasters tropical
  cyclones, tornados, floods, droughts, winter
  storms, extreme heat, extreme cold, lightning, El
  Nino, global warming

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Atmospheric sciences at a glance (cont)

• The modern climatology (meteorology) was born in
  the 1940s (a very young science!), but has been
  growing very fast! Now we have a global
  observational network with many satellites,
  ships, radars and surface stations, as well as
  very comprehensive prediction models running on
  the worlds largest computers.
• The current status of weather and climate
  predictions (1) weather prediction good to 10
  days, (2) tropical cyclone prediction good in
  track but not in intensity, (3) climate
  prediction good to two seasons, (4) climate
  change projections have a 3-fold difference in
  magnitude.
• The main reasons of the difficulties (1)
  Teleconnection problem, (2) Feedback problem, and
  (3) Subgrid-scale problem.

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Evolution of the atmosphere

• The standard units of measurements (SI)
• Earths three atmospheres
• 1st 4.6 billion years ago, H, He
• Transition formation of magnetic
  field, volcano activities
• 2nd 4 billion years ago, CO2, H2O, N2
• Transition emergence of life,
  formation of ocean
• 3rd 400 million years ago, O2
• Important event formation of seven
  continents
• What is the residence time? What is the
  difference between the permanent and variable
  gases? Name 3 of each. What are the most and
  second most abundant gases?
• Given that variable gases are so rare, why are
  they considered at all? How are CO2 and O3
  changing?

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Standard units of measurementSI (System
International)

• Quantity Name Units Symbol
• Length meter m m
• Mass kilogram kg kg
• Time second s s
• Temperature Kelvin K K
• Density kilogram kg/m3 kg/m3
• per cubic meter
• Speed meter per m/s m/s
• second
• Force newton m.kg/s2 N
• Pressure pascal N/m2 Pa
• Energy joule N.m J
• Power watt J/s W

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Evolution of the Sun and the Earth
The Earth was born 4.6 billion years ago.
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Permanent gases and variable gases

• Residence time The amount of time a gas is in
  the atmosphere
• The permanent gases gases having long residence
  times (N242,000,000 y, O25,000 y), 99.999 of
  total atmosphere mass
• The variable gases Gases generally having
  shorter residence times (H2O10 days, CO2150 y).

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Importance of the Variable Gases

• CO2 and water vapor are the major greenhouse
  gases
• Water can exist in all three states on Earth.
  Global water cycle is the process of water being
  cycled from the planet to the atmosphere and back
  again.
• O3 protects us against harmful ultraviolet
  radiation

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What cause the four seasons?

• What is energy? 3 methods of energy transfer
• The names of the 6 wavelength categories in the
  electromagnetic radiation spectrum
• The wavelength range of Sun (shortwave) and Earth
  (longwave) radition
• The two basic motions of the Earth
• What causes the seasons the Earths tilt and the
  3 ways it affects the solar insolation

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Methods of Energy Transfer

• Conduction
• Molecule to molecule transfer
• Heat flow warm to cold
• e.g. leather seats in a car
• Convection
• transferred by vertical movement
• physical mixing
• e.g. boiling water
• Radiation
• propagated without medium (i.e. vacuum)
• solar radiation provides nearly all energy
• The rest of this chapter deals with radiation

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The Electromagnetic Spectrum
Sun shortwave (0.4-0.7 µm) Peak 0.5 µm
(green)
The limitations of the human eye!
Earth longwave (4-100 µm) Peak 10 µm
(infrared)
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The Earths two basic motions revolution with a
period of 1 year, and rotation with a period of 1
day.The change of seasons is caused by the
Earths 23.5o tilt from the line perpendicular to
its orbit plane (toward the sun during summer),
which affects the receipt of solar insolation in
three ways

1. Length of Daylight period
2. Angle at which sunlight hits the surface (Beam
   Spreading)
3. Thickness of atmosphere through which sunlight
   must travel (Beam Depletion)

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What is the greenhouse effect?

• Earths energy balance at the top of the
  atmosphere and at the surface. What percentage of
  solar energy is absorbed by the surface?
• Atmospheric influences on radiation (3 ways)
• What cause the greenhouse effect? What are the
  major greenhouse gases? Why is methane important
  and what contributes most to methane production?
• The three types of atmospheric scattering. What
  causes the blue sky? Why causes the
  reddish-orange sunsets?
• Basic characteristics of global temperature
  distribution (T decreases poleward, isotherm
  shifts seasonally, T over land gt over ocean in
  summer).

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Earths energy budget (averaged over the whole
globe and over a long time
Yellow shortwave
Red longwave
Net Longwave 21
Sensible heat 7
Latent heat 23

• At the top of the atmosphere (3-way balance)
• Incoming shortwave Reflected Shortwave 
  Emitted longwave
• At the surface (5-way balance)
• Incoming shortwave Reflected shortwave
  Net emitted longwave (emitted - incoming)
• Latent
  heat flux sensible heat flux

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Atmospheric absorption - The Greenhouse Effect
Transparent to solar (shortwave) radiation
Opaque to earths (longwave) radiation
Major GH gases CO2, H20(v), CH4
The greenhouse effect helps to keep the earth
surface at a comfortable temperature. But when
its too strong, the temperature becomes too warm.
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The importance of methane (CH4)

• 23 times more powerful as a greenhouse gas than
  CO2
• The livestock sector is a major player, which
  accounts for 35-40 global anthropogenic
  emissions of methane (their burps!)
• The livestock sector is responsible for 18 of
  total greenhouse gas emissions, which is higher
  than transportation (cars, airplanes, etc)
• Therefore, consuming less meat is more efficient
  in reducing global warming than not driving cars.

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What set the atmosphere in motion?

• How thick is the atmosphere compared to the
  earths thickness?
• Four layers of the atmosphere, what separate
  them?
• Definition of pressure and its unit.
• Definition of pressure gradient. Pressure
  gradient sets the air in motion.
• Equation of state (Relationship between P, ?, and
  T)
• Vertical Pressure Distribution. How does pressure
  change with height? What is the hydrostatic
  equilibrium?

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What set the atmosphere in motion? (cont.)

• Know the 3 Forces that affect wind speed
  /direction
• Especially work on Coriolis force, as this is the
  hardest to understand. Which direction is air
  deflected to by Coriolis force?
• What is the geostrophic balance? At which level
  is it valid? Difference between upper level and
  surface winds
• Does cyclones correspond to high or low surface
  pressure? Is the air moving clockwise or
  counter-clockwise around them? How about
  anticyclones?

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Temperature Layers
The names of the 4 layers What separate them? The
approximate height of tropopause, stratopause and
mesopause
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The Equation of State
Pressure density x temperature x 287 J kg-1
K-1 p ?TR

• Describes relationships between pressure,
  temperature, and density (Start w/ molecular
  movement in sealed container ? Pressure
  proportional to rate of collisions between
  molecules and walls).
• At constant temperatures, an increase in air
  density will cause a pressure increase (Add more
  molecules ? increase density ? increase rate of
  collisions ? raise pressure)
• Under constant density, an increase in
  temperature will lead to an increase in pressure
  (Raise temperature ? increase speed of molecules
  ? increase rate of collisions ? raise pressure)

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Vertical Hydrostatic Equilibrium

• Explains why air doesnt continuously blow upward
  or get pulled downward
• The downward force of gravity (weight of parcel)
  is balanced by a strong vertical pressure
  gradient (VPG) ? creates hydrostatic equilibrium
• ?p/?z?g

?p/?z
Vertical Pressure Gradient
weight of parcel
?g
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Forces affecting the horizontal winds

• Horizontal pressure gradients responsible for
  wind generation
• Three forces affecting horizontal winds
• Pressure Gradient Force  (PGF)
• Coriolis Effect  (CE)
• Friction Force (FF)

• CE
• The Earths rotation deflects any moving object
  to the right of its moving direction in NH (left
  in SH). Like walking in a turning bus.
• CE increases poleward (greatest at the poles, 0
  at the equator), and increases with the speed of
  moving object

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Geostrophic Balance (Geostrophic flow)

• PGF - CE
• When the effects of friction can be neglected
  (such as in the upper air away from surface
  roughness), the wind speed/direction is simply a
  balance between the PGF and CE.
• Air motion is deflected by the Coriolis force to
  be perpendicular to PGF

PGF
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Cyclones, Anticyclones, Troughs and Ridges on
weather charts

• Isobars usually closed off at lowest levels
  Cyclones (low pressure), Anticyclones (high
  pressure)
• High pressure areas (anticyclones) - clockwise
  airflow in the Northern Hemisphere (opposite flow
  direction in S. Hemisphere)
• Low pressure areas (cyclones) -
  counterclockwise airflow in N. Hemisphere
  (opposite flow in S. Hemisphere)
• Isobars usually not closed off at highest
  levels Troughs (low pressure), Ridges (high
  pressure)

Highest level ?
? Lowest level
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About the midterm

• There will be 40 multiple-choice questions
• Sample questions

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• In the SI system, the standard unit of length is
• A) yard, B) meter, C) gram, D) pound.
• 2) Which of the following is NOT a variable
  gas?
• A) water vapor. B) nitrogen. C) carbon
  dioxide. D) ozone.
• In the northern hemisphere, when the surface wind
  blows toward the east, the underlying ocean
  current flows toward
• A) the west. B) the north. C) the
  southeast. D) the northwest.
• 4) Anticyclones
• A) are associated with low-pressure systems in
  the northern hemisphere.
• B) experience Coriolis effects that deflect air
  to the left in the Northern Hemisphere.
• C) are associated with supersonic winds.
• D) are associated with counter-clockwise flow in
  the southern hemisphere.