Download Atmospheric Circulation and the Coriolis Effect Concepts Terms

Concepts
high pressure systems
low pressure systems
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converging air at surface
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Terms
atmospheric pressure = weight of air column per unit area
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measured at surface
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“standard” atmospheric pressure at sea level = 1 atmosphere (or 1 atm) by
definition
in more familiar units, 1 atm = 14.7 lbs/in2
dependent on density of air
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warm, moist air = low density
cool, dry air = high density
a pressure gradient exists between high and low pressure
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winds act to try and reduce pressure gradients by flowing from high
pressure to low pressure
the stronger the pressure difference, the stronger the winds
winds are named for the direction from which they originate, NOT the
direction in which they blow
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easterlies – winds that come from the east
westerlies – winds that come from the west
northeasterlies –from the northeast
southeasterlies –from the southeast
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counterclockwise in the
northern hemisphere
clockwise in the southern
hemisphere
associated with
precipitation
and storms
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air sinking from aloft
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warm
laden with water vapor
surface “cyclones”
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A Mighty Wind Is Blowin’ (and Turnin’ Too)
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low density
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Atmospheric Circulation
and the Coriolis Effect
air rising from surface
air cools at high
altitude
water vapor
condenses and
rains out
high density
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cool
dry (can’t hold water vapor)
diverging air at surface
surface “anti-cyclones”
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clockwise in the northern
hemisphere
counter-clockwise in the
southern hemisphere
associated with
dry regions like
deserts
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sinking air has
very little moisture
warms as it sinks,
causing evaporation
from surface
Observations
there are bands or zones
around the Earth that have
greater concentrations of
clouds (=greater
precipitation)
in contrast, there are other
zones which display fewer
clouds and precipitation
(=greater evaporation)
weather patterns in the lower 48
states move from west to east
across the U.S., whereas
weather patterns in the tropics
move from east to west
hurricanes move west in the
tropics and then hook to the
east as they move out of the
tropics
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Bands of cloudiness
Hurricane tracks
continuous line of clouds along the equator
lack of clouds in subtropical regions
another bunch of clouds at midlatitude-to-subpolar regions
tropical easterlies blow hurricanes westward
midlatitude westerlies blow hurricanes eastward
note the general
cloud distribution
Pressure patterns and prevailing winds
Circulation on a non-rotating Earth
cooling:
= sinking cold,
dry air masses
90°N
(North Pole)
the Trades, Westerlies,
and Polar Easterlies
are prevailing winds
Polar Front
60°N
30°N
subtropical high
"horse latitudes"
ITCZ
ITCZ - "doldrums"
0° (Equator)
Intertropical Convergence Zone
subtropical high
"horse latitudes"
30°S
the ITCZ & the horse
latitudes are areas of
very low surface winds
60°S
Polar Front
90°S
Given the unequal distribution
of heat across Earth’s surface,
where would you predict
air masses to rise, and
where would you predict
air masses to sink?
Why then does low pressure
dominate in the tropics
as well as the mid-latitudes,
and why does high pressure
dominate in the subtropics
as well as the poles?
solar heating:
= rising warm,
humid air
(South Pole)
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The Coriolis effect
in the Northern Hemisphere
From the perspective of
looking down on the North
Pole from above, Earth rotates
counter-clockwise, and any
moving body not rigidly
attached to the surface will
undergo an apparent
deflection to the right.
If you take off from the North
Pole in a jet with a heading
toward Chicago, after flying for
hours with the jet on autopilot, you could end up in Los
Angeles.
What is happening?
The Coriolis effect
in the Southern Hemisphere
direction of Earth's rotation
about its axis
Chicago
NY
initial direction
LA
actual flight path
90°N
(North Pole)
Deflection is to the right.
This is known as the
Coriolis Effect and it is
due to the Earth’s rotation.
0°
From the perspective of
looking down on the South
Pole from above, Earth rotates
clockwise, and any moving
body not rigidly attached to
the surface will undergo an
apparent deflection to the left.
If you take off from the South
Pole in a jet with a heading
toward Buenos Aires,
Argentina, after flying for
hours with the jet on autopilot, you could end up in
Santiago, Chile.
But it doesn’t work in a sink!!!
direction of Earth's rotation
about
about it's
its axis
Santiago Chile
actual flight path
Buenos Aires,
Argentina
initial direction
90°S
(South Pole)
Deflection is to the left.
0°
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