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General
Circulation in the Atmosphere |
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General
Circulation in Oceans |
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Air-Sea
Interaction: El Nino |
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Thermally Direct Cells (Hadley and Polar Cells) |
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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. |
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Thermally Indirect Cell (Ferrel Cell) |
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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! |
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(Due
to sea-land contrast and topography) |
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Yes: the
three-cell model explains reasonably well the surface wind distribution in
the atmosphere. |
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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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Pressure and winds associated with Hadley cells
are close approximations of real world conditions |
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Ferrel and Polar cells do not approximate the
real world as well |
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Surface winds poleward of about 30o
do not show the persistence of the trade winds, however, long-term averages
do show a prevalence indicative of the westerlies and polar easterlies |
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For upper air motions, the three-cell model is
unrepresentative |
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The Ferrel cell implies easterlies in the upper
atmosphere where westerlies dominate |
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Overturning implied by the model is false |
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The model does give a good, simplistic
approximation of an earth system devoid of continents and topographic
irregularities |
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The
Aleutian, Icelandic, and Tibetan lows |
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The oceanic (continental) lows achieve maximum
strength during winter (summer) months |
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The summertime Tibetan low is important to the
east-Asia monsoon |
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Siberian,
Hawaiian, and Bermuda-Azores highs |
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The oceanic (continental) highs achieve maximum
strength during summer (winter) months |
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¶U/¶z µ ¶T/¶y |
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The
vertical shear of zonal wind is related to the latitudinal gradient of
temperature. |
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Jet
streams usually are formed above baroclinic zone (such as the polar front). |
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The hurricane is characterized by a strong
thermally direct circulation with the rising of warm air near the center of
the storm and the sinking of cooler air outside. |
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Hurricanes: extreme tropical storms over
Atlantic and eastern Pacific Oceans. |
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Typhoons: extreme tropical storms over western
Pacific Ocean. |
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Cyclones: extreme tropical storms over Indian
Ocean and Australia. |
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Upper
Ocean (~100 m) |
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Shallow, warm upper layer where light is abundant and where most
marine life can be found. |
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Deep
Ocean |
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Cold,
dark, deep ocean where plenty supplies of nutrients and carbon exist. |
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Currents are in geostropic balance |
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Each gyre includes 4 current components: |
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two
boundary currents: western and eastern |
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two
transverse currents: easteward and westward |
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Western boundary current (jet stream of ocean) |
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the fast, deep, and narrow current moves warm water polarward (transport ~50 Sv or greater) |
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Eastern boundary current |
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the
slow, shallow, and broad current moves cold water equatorward (transport ~
10-15 Sv) |
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Trade wind-driven current |
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the moderately shallow and broad westward current (transport ~ 30
Sv) |
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Westerly-driven current |
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the wider and slower (than the trade wind-driven current) eastward
current |
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Western Boundary Current |
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Gulf
Stream (in the North Atlantic) |
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Kuroshio Current (in the North Pacific) |
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Brazil Current (in the South Atlantic) |
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Eastern Australian Current (in the South Pacific) |
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Agulhas Current (in the Indian Ocean) |
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Eastern Boundary Current |
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Canary
Current (in the North Atlantic) |
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California Current (in the North Pacific) |
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Benguela Current (in the South Atlantic) |
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Peru Current (in the South Pacific) |
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Western Australian Current (in the Indian Ocean) |
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The delayed oscillator suggested that oceanic
Rossby and Kevin waves forced by atmospheric wind stress in the central
Pacific provide the phase-transition mechanism (I.e. memory) for the ENSO
cycle. |
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The propagation and reflection of waves,
together with local air-sea coupling,
determine the period of the cycle. |
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Based on the delayed oscillator theory of ENSO,
the ocean basin has to be big enough to produce the “delayed” from ocean
wave propagation and reflection. |
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It can be shown that only the Pacific Ocean is
“big” (wide) enough to produce such delayed for the ENSO cycle. |
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It is generally believed that the Atlantic Ocean
may produce ENSO-like oscillation if external forcing are applied to the
Atlantic Ocean. |
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The Indian Ocean is considered too small to
produce ENSO. |
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“Pacific Decadal Oscillation" (PDO) is a
decadal-scale climate variability that describe an oscillation in northern
Pacific sea surface temperatures (SSTs). |
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PDO is found to link to the decadal variations
of ENSO intensity. |
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The NAO is the dominant mode of winter climate
variability in the North Atlantic region ranging from central North America
to Europe and much into Northern Asia. |
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The NAO is a large scale seesaw in atmospheric
mass between the subtropical high and the polar low. |
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The corresponding index varies from year to
year, but also exhibits a tendency to remain in one phase for intervals
lasting several years. |
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Notes