Transcript Garrison Oceanography 7e Chapter 8

Oceanography
An Invitation to Marine Science, 7th
Tom Garrison
Chapter 8
Circulation of the Atmosphere
8.1: The Atmosphere and Ocean Interact with Each Other
• The interactions of the
atmosphere and ocean
influence our weather and
climate.
– Weather: state of the
atmosphere at a specific
time and place
– Climate: the long-term
statistical view of
weather
• Average temperature
• Average precipitation
8.1: The Atmosphere and Ocean Interact with Each Other
• Atmosphere: volume of gases, water
vapor, and particles surrounding the
Earth
• 4 layers
– Troposphere: the layer of the
atmosphere closest to the Earth
• Weather occurs here
– Stratosphere: the second layer of
the atmosphere
• The Ozone (O3) layer exists
here
– Mesosphere: the 3rd layer
– Thermosphere: the 4th layer
8.2: The Troposphere Is Composed Mainly of Nitrogen,
Oxygen, and Water Vapor
• The lower atmosphere is a fairly homogeneous mixture of gases.
– Nitrogen = 78%
– Oxygen = 21%
– Other compounds = less than 1 %
• Water vapor can occupy up to 4% of the volume of the atmosphere.
– Enters air through evaporation
– If evaporation is high, percentage of water vapor will be higher.
8.2: The Troposphere and the Greenhouse Effect
• Greenhouse effect: the natural trapping of heat in the troposphere to keep
the planet a livable temperature
– Without the greenhouse effect we would freeze
– Greenhouse gases trap the heat
• CO2, methane (CH4), water vapor
– Global warming is caused by too many greenhouse gases that trap too
much heat.
The density of air is influenced by
temperature and water content.
8.2: Air Density and It’s Influence on Weather
• Density = mass/volume = g/cm3
• The density of air is influenced by temperature and water content.
– Warm air is less dense than cold air
– Humid air is less dense than dry air at the same temperature
• Water vapor has less mass than nitrogen and oxygen
• Water vapor rises, expands, and cools
– Cold air holds less water
– It condenses and comes
down as precipitation
8.2: The Stratosphere and the Ozone Layer
• Ozone Layer: Blocks UV rays from hitting the Earth
– Ozone = O3
– Hole (“thinning”) in the Ozone Layer over the poles
– Allows more UV rays to reach the Earth
– Causes?
– Concerns?
8.1 – 8.2 Concept Questions
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Explain the difference between weather and climate.
What are the two major components of climate?
List the four layers of the atmosphere from the ground up.
Explain the significance of the troposphere to life on earth.
Explain how the greenhouse effect works and the major
greenhouse gases.
What is the composition of air in the troposphere?
Explain how air density varies based on temperature.
Explain how air density varies based on water vapor.
Explain what causes precipitation.
How does the ozone layer impact life on earth?
Venn Diagram: Global Warming vs. Ozone Depletion
• Complete in your notebook
• Include at least these 9 points on each side:
– location in atmosphere, location on the earth, natural causes, human
induced causes, impacts to the environment, impacts to human
health, prevention, solutions, laws
– At least 2 similarities in the middle
8.3: The Atmosphere Moves in Response to Uneven Solar
Heating and Earth’s Rotation
• Atmospheric circulation is powered by sunlight.
• 51% of the incoming energy is absorbed by the Earth’s land & water
• Light (short-wave) energy absorbed at the surface is converted into heat.
Heat leaves Earth as infrared (long-wave) radiation.
• Since input equals output over long periods of time, the heat budget is
balanced.
– Thermal equilibrium: it is growing neither warmer or colder
8.3: The Solar Heating of Earth Varies with Latitude
Solar energy input varies with latitude:
• Sun’s rays hit the Earth at varying angles – more direct at the
equator.
•Equal amounts of sunlight are spread over a greater surface
area near the poles than in the tropics.
–Ice near the poles reflects much of the energy that reaches the surface.
8.3: The Solar Heating of Earth Varies with Latitude
Earth as a whole is in thermal equilibrium, but different latitudes are not.
The average annual incoming
solar radiation (red line) absorbed
by Earth is shown along with the
average annual infrared radiation
(blue line) emitted by Earth.
• Polar latitudes lose more heat
to space than they gain
• Tropical latitudes gain more
heat than they lose
• Only at about 38° N and 38° S
latitudes does the amount of
radiation received equal the
amount lost.
• Since the area of heat gained
(orange area) equals the area
of heat lost (blue areas), Earth’s
total heat budget is balanced.
8.3: The Solar Heating of Earth Varies with Latitude
Earth as a whole is in thermal equilibrium, but different latitudes are not.
8.3: The Solar Heating of Earth Also Varies with the Seasons
• Seasons are caused by variations in the amount of incoming
solar energy as Earth makes its annual rotation around the
sun on an axis tilted by 23 ½°.
• Northern Hemisphere winter - receives less light and heat as
the Southern Hemisphere is tilted toward the sun.
• Northern Hemisphere summer - situation is reversed.
8.3: Earth’s Uneven Solar Heating Results in LargeScale Atmospheric Circulation
• Convection currents:
circular current of air (or
water) caused by difference
in air density resulting from
the difference in
temperature
– Warms air, expands,
becomes less dense,
and rises.
– Cool air, contracts,
becomes more dense,
and falls.
8.3 Concept Questions – Part 1
1.
2.
3.
4.
5.
What is meant by thermal equilibrium?
Is the Earth’s heat budget in balance? Why or why not.
Explain how solar heating varies with latitude.
Explain how solar heating varies with seasons.
Describe a convection current.
8.3: Earth’s Uneven Solar Heating Results in LargeScale Atmospheric Circulation
• If uneven solar heating were the
only factor to be considered…
– At the equator, air would
warm, expand, and rise.
– It would move toward the
poles, where it would cool,
become more dense and fall.
• However, we must consider…
the Earth’s rotation.
8.3: Earth’s Uneven Solar Heating Results in Large-Scale
Atmospheric Circulation
• Global circulation of air is controlled by 2 forces:
1. Uneven solar heating
2. Earth’s rotation
• The Coriolis effect is the observed deflection of a
moving object is caused by the moving frame of
reference on the spinning Earth.
8.3: Earth’s Uneven Solar Heating Results in Large-Scale
Atmospheric Circulation
• Coriolis effect: Because the Earth is rotating, instead of
objects traveling in a straight path, the air is deflected.
– In the Northern Hemisphere air turns to the right (clockwise).
– In the Southern Hemisphere air turns to the left
(counterclockwise).
8.3: The Coriolis Effect Deflects the Path of
Moving Objects
From space:
• Cannonball 1 (north) and
cannonball 2 (south), they
travel straight away from
the cannons and fall to
Earth.
From the ground:
• Cannonball 1 veers slightly
east (right) and cannonball
2 veers slightly west (right)
of their intended targets.
The effect depends
on the observer’s
frame of reference.
8.3: Earth’s Uneven Solar Heating Results in
Large-Scale Atmospheric Circulation
8.3: Earth’s Uneven Solar Heating Results in
Large-Scale Atmospheric Circulation
8.3: The Coriolis Effect Influences the Movement of Air in
Atmospheric Circulation Cells
• A large circuit of air is called an atmospheric circulation cell.
• Three cells exist in each hemisphere.
– Hadley cells are tropical cells found on each side of the equator (030oN and 0-30oS).
– Ferrel cells are found at the mid-latitudes (30-60oN and 30-60oS).
– Polar cells are found near the poles (60-90oN and 60-90oS).
8.3: The Coriolis Effect Influences the Movement of
Air in Atmospheric Circulation Cells
• Global air circulation as described in the six-cell circulation model.
• Air rises at the equator and falls at the poles, but instead of one great
circuit in each hemisphere from equator to pole, there are three in each
hemisphere.
8.3 Concept Questions – Part 2
1. Describe the Coriolis effect. How does it differ between the
Northern and Southern Hemisphere?
2. Name the three atmospheric cells that exist in each
hemisphere and describe their location.
3. How does the Coriolis effect influence atmospheric
circulation?
8.4: The Coriolis Effect Influences the Movement of
Air in Atmospheric Circulation Cells
• Wind patterns found WITHIN cells:
– Trade winds are surface winds of Hadley cells.
– Westerlies are surface winds of Ferrel cells.
– Polar Easterlies are surface winds of Polar cells.
8.4: The Coriolis Effect Influences the Movement of Air in
Atmospheric Circulation Cells
• Wind patterns found BETWEEN
cells:
– Horse latitudes are areas of
high atmospheric pressure
between Hadley and Ferrel
cells.
– Sinking, arid air causes the
deserts of the world to be
located at 30 degrees N
and S
– Evaporation exceeds
precipitation so ocean
salinity is high.
8.4: Sea Breezes and Land Breezes Arise
From Uneven Surface Heating
• Sea breeze is cool air from
over the water moving
toward land.
• In the afternoon, the
land is warmer than the
ocean surface, and the
warm air rising from the
land is replaced by an
onshore sea breeze.
8.4: Sea Breezes and Land
Breezes Arise From Uneven
Surface Heating (DAY 2)
• Land breezes occur after
sunset when air warmed by
the land blows toward the
water.
• At night, as the land
cools, the air over the
ocean is now warmer
than the air over the land.
The ocean air rises. Air
flows offshore to replace
it, generating an offshore
land breeze.
8.4: Monsoons Are Wind Patterns That
Change with the Seasons
• Monsoons : local seasonal wind pattern caused by heating
or cooling of the continents
• Results in summers with significant rainfall and winters
with very little.
• Caused by different specific heats of land and water.
• Example: In spring, land heats more rapidly than
ocean leading to summers with heavy rain.
• Common on W. coast of India and southeast Asia.
8.4 Concept Questions
1. Describe the three wind patterns that occur WITHIN the
circulation cells.
2. Explain the circulation pattern that causes the formation of
deserts.
3. Explain the circulation pattern that causes the formation of
tropical rainforests.
4. Explain the process of how land breezes form.
5. Explain the process of how sea breezes form.
6. Why is the atmospheric circulation between the two
hemispheres centered about the meteorological equator
and not the geographical?
7. What’s a monsoon?
8.5: Storms Are Variations in Large-Scale
Atmospheric Circulation
• Storms are regional are regional atmospheric disturbances.
Storms have high winds and most have precipitation.
1. Tropical cyclones occur in tropical regions.
2. Extratropical cyclones occur at the polar front,
between Ferrel and Polar cells, and are winter weather
disturbances.
• Both types of storms are cyclones, or rotating masses of
low-pressure air.
8.5: Extra-tropical Cyclones Form between
Two Air Masses
• Polar front: the boundary between the polar
cell and Ferrel cell.
– Stage 1: Winds move in opposite directions on
each side of the front
– Stage 2: The wave shape enlarges
– Stage 3: A twist will form, precipitation develops
• Counterclockwise in the Northern Hemisphere
8.5: Extra-tropical Cyclones Form between Two Air Masses
8.5: Tropical Cyclones Form Within One Warm,
Humid Air Mass
• Form within the warm, humid Hadley Cells
• Multiple names depending on location:
– Hurricanes = North Atlantic and eastern Pacific
– Typhoons = western Pacific
– Tropical cyclones = Indian Ocean
8.5: Tropical Cyclones Form in One Air Mass
Stage 1
Stage 2
Stage 3
8.5 Concept Questions
1. Explain the difference between an extra-tropical and tropical
cyclone.
2. Explain the formation of an extratropical cyclone (3 stages).
3. Explain the formation of a tropical cyclone (3 stages).
4. Explain why cyclones rotate counterclockwise in the northern
hemisphere.
8.6: The Atlantic Hurricane Season of 2005 was the Most
Destructive Ever Recorded
• Atlantic Hurricane Season: June 1 – November 30
• 2005 season most active ever observed – 31 named storms!
– Hurricanes reached peak activity earlier in their life cycle
– July saw the greatest number of storms in one month (7)