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PowerPoint Presentation - Geophysics 189 Natural Hazards

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Hurricane Jeanne, 2004 Principles of Weather – PowerPoint PPT presentation

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Title: PowerPoint Presentation - Geophysics 189 Natural Hazards


1
Principles of Weather
Hurricane Jeanne, 2004
2
Outline
  • Impact of severe weather
  • Role of solar radiation
  • Properties of water, air masses
  • Effects from Earths rotation

3
Severe Weather
  • Includes thunderstorms, cyclones, floods,
    hurricanes, tornadoes
  • Counting all natural hazard effects, severe
    weather leads to 75 of yearly fatalities and
    damage

4
2004 - Hurricanes Jeanne, Ivan, Frances, and
Charley produced 150 fatalities, 41.5 billion
damage (from NOAA website)
5
Weather vs. Climate
  • Weather condition of the atmosphere at any
    particular time/place
  • Made of several elements
  • Air temperature and pressure
  • Humidity
  • Clouds
  • Precipitation
  • Visibility
  • Wind

6
Weather vs. Climate
  • Climate Average weather
  • Described for a particular region over a
    specified time

7
Atmosphere
  • Thin gas envelope that surrounds the planet
  • Most within 30 km of the surface of the planet
  • Mostly composed of
  • Nitrogen
  • Oxygen
  • Smaller amounts of water, carbon dioxide, ozone
  • Clouds with liquid water and ice
  • Important shields from UV radiation, space junk

8
Atmosphere
  • Made of several layers
  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
  • Weather contained within troposphere
  • From surface to 11 km above, air molecules are
    well stirred, rising and falling in this layer

9
Air pressure
  • Air molecules have weight - exert force on
    surface (atmospheric pressure)
  • Weight of air above, so pressure decreases with
    height
  • Measured in units of pressure (millibars)
  • Sea level atm. pressure 1013 mbar
  • Commonly measured with barometer
  • Height of mercury
  • 1013 mbar 30 inches barometric pressure

10
Air pressure and temperature
  • Packet of air rises
  • Air pressure lower, air expands
  • Temperature related to air molecule speed
  • Expansion lowers speed, lowers temp
  • Rising air expands, cools
  • Packet of air sinks
  • Air pressure higher, air contracts
  • Squeezing leads to more collisions, higher speed,
    higher temp
  • Sinking air contracts, warms

11
Role of Atmospheric Heating
  • Sun provides significant amount of heat
  • Reflected and absorbed
  • Most radiation absorbed in equatorial belt
    (32ºN-34ºS)
  • Polar latitudes have net cooling

12
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13
Fate of Heat
  • Some trapped in rock at surface
  • Some absorbed in water/water vapor in air
  • Different amounts of heat lead to heat transport,
    moving air masses, storms

14
Water and Heat
  • High heat capacity
  • Water and air can move heat around through
    convection
  • Water changing phase - change in heat
  • Ice to water latent heat stored in water
  • Water evaporation latent heat of vaporization
  • Vapor condensation latent heat of condensation

15
Temperature and Water
  • Amount of water in air humidity
  • Higher temperatures mean more water vapor can be
    stored in the air (higher humidity)

16
Back to Air Movement
  • Convection warm air rises, cool air sinks
  • Warm rising air -
  • Pressure, temp lower, less water vapor it can
    hold. Condensation forms clouds.
  • Cool sinking air -
  • Pressure, temp higher, can hold more water vapor.
    Clear skies result.

17
Vertical vs. Horizontal Motion of Air
  • Vertical motions set up pressure differences at
    surface
  • Hot air at surface wants to rise - lower
    pressures at surface
  • Cold air sinking leads to higher pressures at
    surface
  • Horizontal motion from high to low pressures
  • If pressure gradient only force, winds move
    strictly from high to low pressure

18
Examples of Surface Pressures
  • Commonly find high pressures in southwest US in
    summer
  • Arctic in winter - surface high pressures

19
Effects from Rotation
  • Toss a ball on a merry-go-round

Still straight-line motion, but merry-go-round
moves beneath it. Sitting on merry-go-round, it
appears like some force deflected the ball.
20
Coriolis Effect
  • Apparent force due to rotation of Earth (changes
    direction, not speed)
  • Northern Hemisphere winds deflected to right
  • Southern Hemisphere winds deflected to the left
  • Effect greatest near poles, less at equator
  • Important for paths of ocean currents, large
    winds, hurricanes

21
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22
Effects on Winds
  • If just difference in solar radiation (no
    rotation), get simple convection cells (Hadley
    cell)

Too Simple!
23
  • Better description is a 3 cell model
  • Also patterns influenced by continents, seasonal
    variations in radiation

Example fig
24
Jet Streams
  • Narrow high velocity winds that flow west to east
  • Operate high in the atmosphere (10-14 km)
  • 2 main jets
  • Polar more impact on weather
  • Subtropical

25
Polar Jet Stream
  • West-east motion occurs along boundary between
    polar cells and mid-latitude cells
  • High temperature contrast leads to high velocity
    of the jet stream
  • Path is variable, influences movement of large
    air masses
  • Summer over Canada
  • Winter over U.S.

26
Common Polar Jet Stream Path in U.S.
27
Characteristics of Large Air Masses
  • Polar air masses cool
  • Tropical air masses warm
  • Land based air masses dry
  • Water based air masses moist
  • Over North America, dominant direction of motion
    is W-E

28
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29
Fronts
  • Boundaries of air masses
  • Sloping surface separating air masses of
    different temperatures, moisture content
  • Typically where you get clouds, precipitation,
    severe weather

30
Examples of Fronts
31
Fronts
  • Advancing cold front pushes warm air up
  • Can produce clouds, thunderstorms
  • Advancing warm front gentle slope, rises above
    cold front
  • Produces widespread clouds

32
  • Cold front meeting warm front, bends rain

33
Next Time
  • Mid-Latitude Cyclones and Thunderstorms

34
Midterm Exam
Mean 81.7 A 90-100 B 80-89 C 70-79 D 60-69 F
59 and below
35
Problem Questions
  • 2 Compressional forces lead to reverse faults
    (hanging wall moves up)
  • 4 New Madrid region is an old rift zone
  • 9 Earth is 4.6 billion years old (4600 million)
  • 13 Magma viscosity is lowered by higher
    temperatures, lower crystal content, lower SiO2
    (answer all of these)
  • 14 Lake Nyos event was a big carbon dioxide
    burp!

36
Problem Questions
  • 17 P waves can travel through solid, liquid,
    and gas
  • Translational slides move down on weak planar
    surfaces
  • Historical earthquakes in the Rio Grande rift
    (hint here) have been related to extensional
    forces, not compressional forces (answer false)

37
Hints for Next Time
  • Read each question carefully
  • Look for hints in the question
  • Attend class, particularly when video clips are
    presented (not posted on website)
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