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- Basic Structures and Dynamics
- General Circulation in the
Troposphere
- General Circulation in the
Stratosphere
- Wind-Driven Ocean Circulation
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- Thermally Direct Cells (Hadley and Polar Cells)
- Both cells have their rising
branches over warm temperature zones and sinking braches over the cold
temperature zone. Both cells directly convert thermal energy to kinetic
energy.
- Thermally Indirect Cell (Ferrel Cell)
- This cell rises over cold
temperature zone and sinks over warm temperature zone. The cell is not
driven by thermal forcing but driven by eddy (weather systems) forcing.
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- Yes and No!
- (Due to sea-land contrast and
topography)
- Yes: the three-cell model
explains reasonably well the surface wind distribution in the
atmosphere.
- No: the three-cell model can
not explain the circulation pattern in the upper troposphere. (planetary
wave motions are important here.)
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- The Aleutian, Icelandic, and
Tibetan lows
- The oceanic (continental) lows achieve maximum strength during winter
(summer) months
- The summertime Tibetan low is important to the east-Asia monsoon
- Siberian, Hawaiian, and
Bermuda-Azores highs
- The oceanic (continental) highs achieve maximum strength during summer
(winter) months
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- ¶U/¶z µ - ¶T/¶y
- The vertical shear of zonal wind
is related to the latitudinal gradient of temperature.
- Jet streams usually are formed
above baroclinic zone (such as the polar front).
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- Temperature differences between the equator and poles
- The rate of rotation of the Earth.
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- Carl Rossby mathematically expressed relationships between mid-latitude
cyclones and the upper air during WWII.
- Mid-latitude cyclones are a large-scale waves (now called Rossby waves)
that grow from the “baroclinic” instabiloity associated with the
north-south temperature differences in middle latitudes.
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- Bjerknes, the founder of the
Bergen school of meteorology, developed polar front theory during WWI to
describe the formation, growth, and dissipation of mid-latitude
cyclones.
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- Every other year or so the normal
winter pattern of a cold polar stratosphere with a westerly vortex is
interrupted in the middle winter.
- The polar vortex can completely
disappear for a period of a few weeks.
- During the sudden warming period,
the stratospheric temperatures can rise as much as 40°K in a few days!
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- The decrease in ozone near the South Pole is most striking near the
spring time (October).
- During the rest of the year, ozone levels have remained close to normal
in the region.
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- In winter the polar stratosphere is so cold (-80°C or below) that
certain trace atmospheric constituents can condense.
- These clouds are called “polar stratospheric clouds” (PSCs).
- The particles that form typically consist of a mixture of water and
nitric acid (HNO3).
- The PSCs alter the chemistry of the lower stratosphere in two ways:
- (1) by coupling between the
odd nitrogen and chlorine cycles
- (2) by providing surfaces on
which heterogeneous reactions can occur.
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- Long Antarctic winter (May through September)
- The stratosphere is cold enough to form PSCs
- PSCs deplete odd nitrogen (NO)
- Help convert unreactive forms of chlorine (ClONO2 and HCl) into more
reactive forms (such as Cl2).
- The reactive chlorine remains bound to the surface of clouds particles.
- Sunlight returns in springtime (September)
- The sunlight releases reactive chlorine from the particle surface.
- The chlorine destroy ozone in October.
- Ozone hole appears.
- At the end of winter, the polar vortex breaks down.
- Allow fresh ozone and odd nitrogen to be brought in from low latitudes.
- The ozone hole recovers (disappears) until next October.
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- Upper Ocean (~100 m)
- Shallow, warm upper layer
where light is abundant and where most marine life can be found.
- Deep Ocean
- Cold, dark, deep ocean where
plenty supplies of nutrients and carbon exist.
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- Currents are in geostropic balance
- Each gyre includes 4 current components:
- two boundary currents:
western and eastern
- two transverse currents:
easteward and westward
- Western boundary current (jet stream of ocean)
- the fast, deep, and narrow
current moves warm water polarward
(transport ~50 Sv or greater)
- Eastern boundary current
- the slow, shallow, and broad
current moves cold water equatorward (transport ~ 10-15 Sv)
- Trade wind-driven current
- the moderately shallow and
broad westward current (transport ~ 30 Sv)
- Westerly-driven current
- the wider and slower (than
the trade wind-driven current) eastward current
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- Western Boundary Current
- Gulf Stream (in the North
Atlantic)
- Kuroshio Current (in the
North Pacific)
- Brazil Current (in the
South Atlantic)
- Eastern Australian Current
(in the South Pacific)
- Agulhas Current (in the
Indian Ocean)
- Eastern Boundary Current
- Canary Current (in the North
Atlantic)
- California Current (in the
North Pacific)
- Benguela Current (in the
South Atlantic)
- Peru Current (in the South
Pacific)
- Western Australian Current
(in the Indian Ocean)
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- Mixed Layer
- Currents controlled by
frictional force + Coriolis force
- à wind-driven circulation
- à Ekman transport (horizontal direction)
- à convergence/divergence
- à downwelling/upwelling at the bottom of mixed
layer
- Thermocline
- downwelling/upwelling in the
mixed layer
- à pressure gradient force + Coriolis force
- à geostrophic current
- à Sverdrup transport (horizontal)
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- Thermo è temperature
- Haline è salinity
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- If we date a water parcel from
the time that it leaves the surface and sink into the deep ocean
- è Then the
youngest water is in the deep north Atlantic, and the oldest water is in
the deep northern Pacific, where its age is estimated to be 1000 year.
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- the waters in the deep northern
Pacific.
- The man-released CFC and the
chemical tritium and C14, which were released through
atmospheric atomic bomb test in the 1950s and 1960s, entered the deep
ocean in the northern Atlantic and are still moving southward slowly.
- Those pollutions just cross the
equator in the Atlantic è They have not reached the deep northern Pacific
yet!!
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- If the warming is slow
- The salinity is high enough to
still produce a thermohaline
circulation
- The circulation will transfer the heat to deep ocean
- The warming in the atmosphere will be deferred.
- If the warming is fast
- Surface ocean becomes so warm
(low water density)
- No more thermohalione circulation
- The rate of global warming in the atmosphere will increase.
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