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Basic
Dynamics |
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General Circulation in the Troposphere |
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General
Circulation in the Stratosphere |
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Climate
Variability in the Troposphere and Stratosphere |
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Climate
Feedback Processes in the Atmosphere |
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Tornadoes can rotate in either cyclonic
(counterclockwise) or anticyclonic (clockwise) directions. |
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However, the majority of the tornadoes in the
Northern Hemisphere rotate in the cyclonic direction. |
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Geostrophic Wind |
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pressure gradient force = Coriolis force |
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Cyclostrophic Wind |
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pressure gradient force = centrifugal force |
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Gradient
Wind |
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pressure gradident force + Coriolis force + centrifugal force = 0 |
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Inertia
Motion |
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No
pressure gradient force. Coriolis force = centrifugal force. |
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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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¶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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Sudden
Warming: in Northern Pole |
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Quasi-Biennial Oscillation (QBO): at the equator |
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Ozone
Hole: in Southern Pole |
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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. |
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The
polar vortex can completely disappear for a period of a few weeks. |
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During
the sudden warming period, the stratospheric temperatures can rise as much
as 40°K in a few days! |
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Planetary-scale waves propagating from the troposphere
(produced by big mountains) into the stratosphere. |
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Those
waves interact with the polar vortex to break down the polar vortex. |
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There
are no big mountains in the Southern Hemisphere to produce planetary-scale
waves. |
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No
sudden warming in the southern polar vortex. |
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Notes