CHAPTER 6 Air-Sea
Interaction
1. Overview
- Atmosphere and ocean one interdependent system
- Solar energy creates winds
- Winds drive surface ocean currents and waves
- Examples of interactions:
- El Niño-Southern Oscillation
- Greenhouse effect
2. Seasons
- Earth’s axis of rotation tilted with respect to ecliptic - 23.5 o
- Ecliptic = plane traced by Earth’s orbit
- Tilt responsible for seasons
- Vernal (spring) equinox
- Summer solstice
- Autumnal equinox
- Winter solstice
- Seasonal changes and day/night cause unequal solar heating of
Earth’s surface
3. Figure 6.1. Seasons
4. Uneven solar heating
- Angle of incidence of solar rays per area
- Equatorial regions more heat
- Polar regions less heat
- Thickness of atmosphere
- Albedo
- (= white)->% of incident radiation that is reflected back to
space
- Average = ~30%
- Day/night
- Seasons
5. Figure 6.3: surface heat profile
6. Oceanic heat flow
- High latitudes more heat lost than gained
- Due to albedo of ice
- high incidence of solar rays
- If sun is only 5o above horizon, 40% reflected
- Low latitudes more heat gained than lost
- Only 2% reflected if smooth sea, 90o overhead
7. Figure: Physical properties of the atmosphere
(Temperature Vs. altitude)
- Atmosphere
- Temperature profile of lower atmosphere
- Troposphere – temperature cools with increasing altitude
8. Figure 6.5: Physical properties of atmosphere
- Warm air, less dense (rises)
- Cool air, more dense (sinks)
- Moist air, less dense (rises)
- Dry air, more dense (sinks)
9. Air pressure
- Atmospheric pressure at sea level
- 1 atmosphere
- 14.7 lbs/in2
- 760 mm Hg
- Decreases with altitude
- Increases with depth
- + 1 atmosphere for every 33 ft or 10 m
- Martini's Law (Nitrogen Narcosis) mental effect of each 50 ft of
descent breathing compressed air; is approximately equivalent to that
of one (American-style) dry martini, starting at 100 ft.
10. Movements in atmosphere
- Air (wind) always moves from regions of high pressure to low
- Cool dense air, higher surface pressure
- Warm less dense air, lower surface pressure
11. Movements in Air: Fig. 6.7
- Air (wind) always moves from regions of high pressure to low
- Convection or circulation cell
12. Movements in air on a rotating Earth
- Coriolis effect causes deflection in moving body
- Due to Earth’s rotation to east
- Most pronounced on objects that move long distances across
latitudes
- Deflection to right in Northern Hemisphere
- Deflection to left in Southern Hemisphere
- Maximum Coriolis effect at poles
- No Coriolis effect at equator
13. Do toilets in the N flush clockwise and in the Southern
hemispheres flush counterclockwise?
- The twisting effect of the Coriolis force is real and does
influence certain large things like the movement of air masses
- The effect is so small that it plays no role in determining the
direction in which water rotates as it exits from a draining sink or
toilet.
- The Coriolis effect produces a measurable effect over huge
distances and long periods of time, neither of which applies to your
bathroom.
- Toilets and sinks drain in the directions they do because
of the way water is directed into them or pulled from them. If water
enters in a swirling motion (as it does when a toilet is flushed, for
example), the water will exit in that same swirling pattern; as well,
most basins have irregular surfaces and are not perfectly level,
factors which influence the direction in which water spirals down their
drains.
- The configuration of taps and drains is responsible for the
direction of spin given to water draining from sinks and bathtubs to a
degree that overwhelms the slight influence of the Coriolis force.
- From: www.snopes.com/science/coriolis.htm
14. Coriolis effect and missile paths (fig. 6.9)
- a: velocity of a point varies with latitude
- b: path if shot from N. pole or from Galapagos toward New Orleans
15. Global atmospheric circulation patterns
- Circulation cells form as air changes density due to:
- Changes in air temperature
- Changes in water vapor content
- Circulation cells
- Hadley cells (0o to 30o N and S)
- Ferrel cells (30o to 60o N and S)
- Polar cells (60o to 90o N and S)
16. Global atmospheric circulation
- Subtropical highs
- Polar highs
- Clear skies
- Low pressure zones
- Equatorial low
- Subpolar lows
- Overcast skies with lots of precipitation
17. Atmospheric circulation and wind belts of the world (Fig.
6.10)
- 3 cell model creates major wind belts
- Polar easterlies
- Prevailing westerlies
- Trades (NE and SE)
- General pattern modified by seasonal changes and continents
18. Global wind belts
- Trade winds
- Northeast trades in Northern Hemisphere
- Southeast trades in Southern Hemisphere
- Prevailing westerlies
- Polar easterlies
- Boundaries between wind belts
- Doldrums or Intertropical Convergence Zone (ITCZ)
- Horse latitudes
- Polar fronts
19. Modifications to idealized 3-cell model of atmospheric
circulation
- More complex in nature due to
- Seasonal changes
- Distribution of continents and ocean
- Differences in heat capacity between continents and ocean
20. January sea-level atmospheric pressures and winds: Arrows
show direction of winds, which move from high-to low-pressure regions.
21. Ocean weather and climate patterns
- Weather – conditions of atmosphere at particular time and place
- Climate – long-term average of weather
- Northern hemisphere winds move counterclockwise (cyclonic) around
a low pressure region
- Southern hemisphere winds move clockwise (anticyclonic) around a
low pressure region
22. High- and low-pressure regions and air flow. In N.
Hemisphere: (High) Righty tighty, (low) lefty loosie?
23. Coastal winds
- Solar heating
- Different heat capacities of land and water
- Sea breeze
- From ocean to land
- Land breeze
- From land to ocean
24. Fronts and storms (Figure 6.14)
- Air masses meet at fronts
- Storms typically develop at fronts
25. www.weather.com for 5Mar2006
- Cold front
- Warm front
- Occluded front
- High (H) pressure
- Low (L) pressure
26. Warm front: contact between warm air mass moving into
cold air
Cold front: contact between cold air mass moving into warm air
- Jet stream:
- fast moving, east to west
- just above the troposphere (6 mi high)
- can steer polar air masses or tropical air masses to cause
unusual weather
27. Tropical cyclones (hurricanes) (Figure 6.16)
- Large rotating masses of low pressure
- Strong winds, torrential rain
- Classified by maximum sustained wind speed
28. What do you call it?
- Tropical depression: winds less than 61 kph (38 mph)
- Tropical storm: winds between 61 - 120 kph (38 - 74 mph)
- Tropical cyclone
- Winds exceed 120 kph (74 mph)
- Hurricanes (N & S America)
- Typhoons: W. North Pacific
- Cyclones: Indian Ocean
29. Saffir-Simpson Scale: Table 6.5
30. Hurricane morphology and movement: Typical N. Atlantic
hurricane storm track and internal structure (Figure 6.17)
31. Hurricane destruction
- Fast winds
- Flooding from torrential rains
- Storm surge most damaging
- Historical examples:
- Galveston, TX, 1900
- Hurricane Andrew, 1992
- Hurricane Mitch, 1998
- Katrina, 2005
32. Photographs: Galveston, Texas 1900 - 8000 died
33. Katrina KO’d Andrew as the most destructive hurricane
- 1,300 fatalities
- $100 - 200 billion in damages
- Insured damage at $12.5 billion
- 1 million non-farm jobs lost
- Damaged oil infrastructure -> high gas prices
- 20 offshore platforms missing, sunk or adrift
- Refineries shut down
- Highways damaged
- Ports shut down (imported oil brought in)
- Other impacts: gambling, ag, forestry, bankruptcies
34. Figure 6.18. As a tropical cyclone moves ashore,
low-pressure + strong onshore winds = high-water storm surge.
35. Ocean’s climate patterns
- Open ocean’s climate regions parallel to latitude
- May be modified by surface ocean currents
- Equatorial regions – warm, lots of rain
- Tropical regions – warm, less rain, trade winds
- Subtropical regions – rather warm, high rate of evaporation, weak
winds
36. Ocean’s climate patterns
- Temperate regions – strong westerlies
- Subpolar regions – cool, winter sea ice, lots of snow
- Polar regions – cold, sea ice, polar high pressure
37. Ocean’s climate patterns Fig. 6.2.
38. Polar oceans and sea ice
- Sea ice or masses of frozen seawater form in high latitude oceans
- Begins as small needle-like ice crystals
- Slush turns into thin sheets that break into
- Pancake ice that coalesce to
- Ice floes
- Rate of formation depends on temperature
39. Sea Ice is less salty
- As ice forms, leaves most of the dissolved components behind
- Cold, higher density (saltier) water left below --> sinks
- Less dense water rises --> freezes
- Ice is a poor conductor --> freezing process slows as ice
builds up
40. Sea ice: Aerial view of the Larsen ice shelf on the
Antarctic Peninsula, where ribbons of sea ice remain seaward of the
shelf.
41. Polar oceans and icebergs (Fig. 6.22)
- Icebergs – fragments of glaciers or shelf ice
- Not salty - Why?
42. Greenhouse effect- Figure 6.23
- Trace atmosphere gases absorb heat reradiated from surface of
Earth
- Infrared radiation released by Earth
- Solar radiation mostly ultraviolet and visible region of
electromagnetic spectrum
43. Earth’s heat budget Fig. 6.24
- Earth maintained a nearly constant average temperature because of
equal rates of heat gain and heat loss
44. Greenhouse gases (Fig. 6.25)
- Absorb longer wave radiation from Earth
- Water vapor
- Carbon dioxide (CO2)
- Other trace gases: methane, nitrous oxide, ozone, and
chlorofluorocarbons
45. Global warming over last 100 years
- Average global temperature increased
- Part of warming due to anthropogenic greenhouse (heat-trapping)
gases such as CO2
46. Fig. 6.26: CO2 concentrations: ice core data
47. Mauna Loa Observatory, HawaiiMonthly Average [CO2]
48. Photographs: Ice Cores: windows into the climate
740,000 years ago
49. Quote: Global Climate Change
- The observed increase in global mean temperature over the last
century is unlikely to be entirely natural in origin . . . The balance
of evidence suggests that there is a discernible human influence on
global climate. UN Intergovernmental Panel on Climate Change (IPCC) 1995
50. Possible consequences of global warming
- Melting glaciers
- Shift in species distribution
- Warmer oceans
- More frequent and more intense storms
- Changes in deep ocean circulation
- Shifts in areas of rain/drought
- Rising sea level
51. Factors Influencing Climate
- Solar Radiation
- Visible light (l 400 - 700 nm)
- Photosynthetically active radiation (PAR)
- Most of the sun’s energy
- Ultraviolet light, UV (l 200 - 400 nm)
- high energy
- Most doesn’t reach surface, absorbed by atmosphere
- Infrared radiation (IR) (l 700 - 106 nm)
- Primarily absorbed by CO2, H2O vapor and other gases in the
troposphere.
- What is left warms the surface: land, water, vegetation,
animals
52. Greenhouse Effect
- Solar radiation enters the atmosphere
- 47% is passed through to be absorbed at the Earth’s surface
- 17% is absorbed by the lower atmosphere (troposphere) by CO2
and H2O vapor (+ other greenhouse gases)
- Heats the atmosphere
- Acts like the glass of a greenhouse
- = radiative forcing: lets the VIS portion pass, but holds the
IR
- 36% is re-radiated back to space
53. Fig 12.1. Solar radiation is responsible for creating a
habitable environment on the earth => the greenhouse
effect. Without GE = Earth’s surface would be ~ -15 oC.
54. Table: Greenhouse Gases -->Sources of CO2 -
55. CO2 Sinks
- Definition: remove CO2 from the atmosphere
- Processes
- fix into vegetation (land, ocean)
- coral building: corals and coralline algae
- Diffusion into oceanic waters
- CO2 dissolves into water --> carbonates, bicarbonates
- CO2 is currently being added faster than it is removed by sinks
- Normal sink process slow: If 1000 molecules released,
1000 years ago, 985 dissolved in ocean
- Today: for every 1000 molecules, only 836 will dissolve: leaves
160 in the atmosphere
56. EPA graphic: Local Temperatre Change and CO2 Concentrations
over the past 160,000 years
57. Sulfate Aerosols & Global Cooling
- Very small solid particulate matter
- Action: reflect a fraction of incoming solar E
- Cooling action short: particles precipitate out
- Sources:
- 1991: Mt. Pinatubo (Philippines), Mt. Hudson (Chile) -- 60
million tons of SO2
- SO2 reacts with O2 => sulfate aerosols
- 1991-1992: atmosphere cooled ~ 0.5 oC
- 1994: reversal --> hottest year on record
- Combustion of fossil fuels, coal-fired industry
58. Other Greenhouse Gases
- Methane
- Source: methanogenic bacteria: swamps, wetlands, animal
GI systems
- Effect: radiative forcing 20X CO2/molecule
- Anthropogenic rise: 2X
- N2O: nitrous oxide
- Source: bacterial decomposition, forest fires
- Effect: radiative forcing 200 X CO2/molecule
- Anthropogenic rise: minimal
- Chlorofluorocarbons (CFCs)
- Source: coolant in refrigerators, freezers, air
conditioners; propellants, foam manufacture
- Effect: radiative forcing: 10,000 X CO2/molecule
- Anthropogenic rise: all [atmospheric]
59. Fig 12.2. Relative contributions of greenhouse gases to
global warming as a result of radiative forcing.
60. For More Information
http://yosemite.epa.gov/OAR/
globalwarming.nsf/content/
ResourceCenterPresentationsGHGEmissions.html
61. Reducing greenhouse gases
- Greater fuel efficiency
- Alternative fuels
- Re-forestation
- Eliminate chlorofluorocarbons
- Reduce CO2 emissions
- Intergovernmental Panel on Climate Change 1988
- Kyoto Protocol 1997
62. Ocean’s role in reducing CO2
- Oceans absorbs CO2 from atmosphere
- CO2 incorporated in organisms and carbonate shells (tests)
- Stored as biogenous calcareous sediments and fossil fuels
- Ocean is repository or sink for CO2
- Add iron to tropical oceans to “fertilize” oceans (increase
biologic productivity)