1. Chapter 6 Air–Sea Interaction
Essentials of Oceanography
7th Edition

2. Uneven solar heating on Earth
Solar energy in high latitudes:
Has a larger “footprint”
Is reflected to a greater extent
Passes through more atmosphere
Is less than that received in low latitudes
Figure 6-1

3. Earth’s seasons Earth’s axis is tilted 23½º from vertical
Northern and Southern Hemispheres are alternately tilted toward and away from the Sun
Causes longer days and more intense solar radiation during summer
Figure 6-2

4. Oceanic heat flow A net heat gain is experienced in low latitudes
A net heat loss is experienced in high latitudes
Heat gain and loss are balanced by oceanic and atmospheric circulation
Figure 6-3

5. Physical properties of the atmosphere: Composition (dry air)
Gas
Percent
Nitrogen (N2)
78.1%
Oxygen (O2)
20.9%
Argon (Ar)
0.9%
Carbon dioxide (CO2)
0.036%
All others
Trace

6. Physical properties of the atmosphere: Temperature
Troposphere is:
Lowermost part of the atmosphere
Where most weather occurs
Temperature of troposphere cools with increasing altitude
Figure 6-4

7. Physical properties of the atmosphere: Density
Warm, low density air rises
Cool, high density air sinks
Creates circular- moving loop of air (convection cell)
Figure 6-5

8. Physical properties of the atmosphere: Water vapor
Cool air cannot hold much water vapor, so is typically dry
Warm air can hold more water vapor, so is typically moist
Water vapor decreases the density of air

9. Physical properties of the atmosphere: Pressure
A column of cool, dense air causes high pressure at the surface, which will lead to sinking air
A column of warm, less dense air causes low pressure at the surface, which will lead to rising air
Figure 6-6

10. Physical properties of the atmosphere: Movement
Air always moves from high-pressure regions toward low-pressure regions
Moving air is called wind

11. The Coriolis effect The Coriolis effect
Is a result of Earth’s rotation
Causes moving objects to follow curved paths:
In Northern Hemisphere, curvature is to right
In Southern Hemisphere, curvature is to left
Changes with latitude:
No Coriolis effect at Equator
Maximum Coriolis effect at poles

12. A merry-go-round as an example of the Coriolis effect
To an observer above the merry-go-round, objects travel straight
To an observer on the merry-go-round, objects follow curved paths
Internet video of balls being rolled across a moving merry-go-round
Figure 6-8

13. The Coriolis effect on Earth
As Earth rotates, different latitudes travel at different speeds
The change in speed with latitude causes the Coriolis effect
Figure 6-9a

14. Missile paths demonstrate the Coriolis effect
Two missiles are fired toward a target in the Northern Hemisphere
Both missiles curve to the right
Figure 6-9b

15. Coriolis Force Fc = fV=2ΩsinΦV f=Coriolis parameter Ω=2Π/86164s=7
Coriolis Force Fc = fV=2ΩsinΦV f=Coriolis parameter Ω=2Π/86164s=7.29x10^-5, Φ=latitude, V=speed
The magnitude of the Coriolis force increases from zero at the Equator to a maximum at the poles.
The Coriolis force acts at right angles to the direction of motion, so as to cause deflection to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.

16. If the earth is a cylinder shape and rotating about its axis, will there still any Coriolis effect exists?
The answer is NO.

17. Coriolis effect
The missile trajectories is little affected by the Coriolis force, because missile travels at high speed.
Winds and ocean currents are significantly affected by the Coriolis force.
(ex) at Φ=45, V=0.5 m/s (~1 knot)
water travels 1800 m in an hour,
The earth beneath moves about 300 m.

18. Vertical view of air pressure (global convection)
High Pressure
Low Pressure
Low Pressure

19. Non rotating view of Atmospheric Circulation

20. Wind belts of the world
Figure 6-10

21. General Wind Patterns
Sailors have a special term for the calm, equatorial regions where low pressure persists and little winds exist; the doldrums無風帶
Sailors also have a special term for the regions within the high pressure band, where winds are light and variable; the horse latitudes馬緯度
Places between the high and low pressure bands, on the other hand, experience rapidly moving air, and are characterized by strong, dependable winds

22. (Horse latitudes)

23. Characteristics of wind belts and boundaries
Region/Latitude
Wind belt or boundary name
Characteristic
Equatorial (0-5º)
Doldrums
Low press. boundary
5-30º
Trade winds
Persistent easterlies
30º
Horse latitudes
High press. boundary
30-60º
Prevailing westerlies
Mid-latitude winds
60º
Polar front
60-90º
Polar easterlies
Cool easterly winds
Polar (90º)
Polar high pressure

24. Coriolis effect influences air movement
Northern Hemisphere winds curve to the right as they move from high to low pressure
Causes wind to circulate:
Clockwise around high-pressure regions
Counterclockwise around low-pressure regions
Figure 6-12

25. Air masses that affect U.S. weather
Figure 6-14

26. Sea Breeze 海風
Development of a sea breeze and a land breeze. At the surface, a sea breeze blows from the water onto the land...

27. Land Breeze 陸風
the land breeze blows from the land out over the water. Notice that the pressure at the surface changes more rapidly with the sea breeze. This situation indicates a stronger pressure gradient force and higher winds with a sea breeze.

28. Seasonally Changing Winds
Monsoon Wind System季風 – changes directions seasonally – blows from one direction in summer and the opposite direction in the winter.
Especially well-developed in eastern and southern Asia
During winter, air over the continent becomes much colder than air over ocean. High pressure sets up over Siberia and air flows from land to the ocean….

29. Changing annual wind flow patterns associated with the winter Asian monsoon. Clear skies and winds blow
from land to sea
Changing annual wind flow patterns associated with the summer Asian monsoon. Warm humid air blows up from equator bringing rainy weather.

30. Origin and paths of tropical cyclones
Tropical cyclones are intense low pressure storms created by:
Warm water
Moist air
Coriolis effect
Includes:
Hurricanes颶風
Cyclones氣旋
Typhoons颱風
Figure 6-16

31. Hurricane occurrence
Hurricanes have wind speeds of at least 120 kilometers (74 miles) per hour
Worldwide, about 100 storms grow to hurricane status each year
In the Northern Hemisphere, hurricane season is generally between June 1 and November 30
Current state of the tropical oceans

32. Hurricane structure Hurricanes have:
Circular cloud bands that produce torrential rain
The ability to move into the mid-latitudes
A central eye
Figure 6-17
Figure 6-19a

33. Hurricanes produce storm surge
Is a rise in sea level created by hurricane coming ashore
Can be up to 12 meters (40 feet) high
Causes most destruction and fatalities associated with hurricanes
Figure 6-18

34. Climate regions of the ocean
Figure 6-20

35. How a greenhouse works
Sunlight passes through the clear covering of a greenhouse
It converts to longer wavelength heat energy
Heat cannot pass through the covering and is trapped inside
Figure 6-21

36. The heating of Earth’s atmosphere
Figure 6-23

37. Anthropogenic gases that contribute to the greenhouse effect
Greenhouse Gas
Relative contribution
Carbon dioxide (CO2)
60%
Methane (CH4)
15%
Nitrous oxide (N2O) 5%
Tropospheric ozone (O3) 8%
CFC-11 4%
CFC-12

38. Carbon dioxide is increasing in the atmosphere
As a result of human activities, carbon dioxide in the atmosphere has increased by 30% since 200 years ago
Figure 6-24

39. Earth’s average temperature is rising
Earth’s average surface temperature has risen at least 0.6°C (1.1°F) in the last 130 years
May be related to increase in atmospheric carbon dioxide
Figure 6-25

40. Predicted changes with increased greenhouse warming
Higher than normal sea surface temperatures that could affect world climate
More severe droughts or increased precipitation
Water contamination and outbreaks of water-borne diseases
Longer and more intense heat waves
Shifts in the distribution of plants and animals
Potential melting or enlargement of polar ice caps

41. Essentials of Oceanography 7th Edition
End of Chapter 6
Essentials of Oceanography
7th Edition