Download 8.2.1 and 8.2.3 Atmospheric Pressure

BHS Earth & Space Science
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We all have a column of atmosphere pressing
down on us.
Each 1cm2 column of air has a mass of about
1.03kg.
The average person has ~1,000kg of air
weighing down on them!
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4267m
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2743m
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305m
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The weight of the atmosphere pushes
on the pool of mercury and forces it
up the central column.
Measuring the height of the column
gives a pressure reading in mm of
mercury (mmHg).
These are no longer manufactured in
Europe because mercury is
ridiculously toxic.
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So if mercury is toxic, why not use something
else, like water?
Being much less dense than Hg, a water
barometer would need to be 10m tall!
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The world’s largest
barometer.
Designed to cover up
a huge pipe no one
knew what to do with!
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Impress your special sweetie this Valentine’s
Day by busting out this vocab term.
As warm air expands and rises (being less
dense), it cools. Adiabatically.
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On a clear night, temperature drops much
faster than when it’s overcast.
The warm ground radiates infrared back into
the atmosphere, and with no clouds in the
sky, it flies off into space.
H2O, CH4 and CO2 readily absorb infrared
radiation and thereby trap heat – they are
greenhouse gases.
BHS Earth & Space Science
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The amount of water vapor in the air.
Absolute humidity: the mass of water (g) in a
volume of air (m3)
Relative humidity: the percentages they talk
about on the news.
𝑅𝐻(%) =
𝑎𝑐𝑡𝑢𝑎𝑙 𝑣𝑎𝑝𝑜𝑟 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
. 100
𝑠𝑎𝑡𝑢𝑟𝑎𝑡𝑖𝑜𝑛 𝑣𝑎𝑝𝑜𝑟 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
RH depends on temperature. At 20°C,
saturation occurs at 17.3g/m3.
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When air is saturated we commonly say that
the air can’t “hold” any more water vapor.
What is actually happening: the system has
reached equilibrium - for each water
molecule that changes from liquid to gas,
another condenses from gas to liquid.
Water molecules move much too fast for
anything to literally hold them.
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Warm air can “hold” more vapor than cooler
air. So every winter, you wake up to this:
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As temperature drops overnight, it hits the
dew point, where the air is saturated.
The excess water vapor condenses onto your
windshield.
Now you can explain dew and frost to your
astonished relatives! Yay!
BHS Earth & Space Science
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A cloud forms as a result of warm air rising
and cooling to its dew point, causing water
vapor to condense in the atmosphere.
The tiny water droplets form around
condensation nuclei: microscopic particles of
ash or dust.
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This is a big one for we Front Range dwellers.
As an air mass approaches a mountain, it is
forced to rise and cool.
Once the dew point is reached, a cloud forms.
Those clouds then deposit their precious
moisture on us!
And that is why skiing is so expensive. Oh,
wait…that’s supply and demand.
BHS Earth & Space Science
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1735 – George Hadley proposed that the
trade winds were formed when hot, rising air
near the equator moved north and south and
cooled and sank back towards the surface.
This creates planetary winds.
Predicted Earth’s rotation caused these winds
to deflect to the right in the Northern
Hemisphere and to the left in the Southern.
These large-scale convection cells are called
Hadley cells.
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A narrow band of strong wind blowing west
to east at the interface (boundary) between
air masses of different density.
They travel at speeds >100km/h and may
stretch over thousands of miles in the upper
troposphere.
The jet stream from Hawaii to California is
called the Pineapple Express. Really.
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Global wind systems are influenced by the
rotation of the Earth’s surface beneath them.
Air does not flow directly from high to low
pressure, but is deflected to the right in the
N. Hemisphere and to the left in the S.
Hemisphere.
Air in the N. Hemisphere flows clockwise
around high-pressure areas and counterclockwise around low-pressure areas.
In S. Hemisphere, directions are reversed.
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Let’s see that in action! Coriolis Effect
Animation
Shout-out to Gustave-Gaspard de Coriolis, a
French engineer, who discovered this effect in
1835.
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A large unit of air with the same temperature
and pressure can be treated as a single mass.
When air masses meet and interact, they form
one of four types of front:
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Warm
Cold
Stationary
Occluded