Weather Chp. 27
I.
Atmospheric Moisture
a. Phase changes of water are accompanied by a
change in thermal energy of water
b. HumidityA measure of the amount of water vapor in the air
c. Relative Humiditythe ratio of the amount of water vapor currently in
the air at a given temperature to the largest amount
of water vapor the air can contain at that temp.
i. =
Water vapor in air
Possible water vapor at that temp.
ii. Ex. 50% relative humidity - means the water
content in the air is half the amount it could be.
iii. Warm air can hold more water than cold air
d. As air rises it expands because of lower pressure
e. Expanding air cools
f. As air cools it slows down and begins to condense
(water is polar)- occurs at the dew point
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g. As the water droplets grow they fall as rain, sleet,
hail or snow - precipitation
II. Air Behavior
a. Temperature changes in air is due only to pressure
changes
b. Upper regions of air are warmer than lower regions
leads to a temperature
Inversion
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E.g. Denver’s smog problem
If no wind - Cold air above holds pollution under it,
low to the ground
★Air rises as long as it is less dense than the air
above it.
III.
(figure 27.7)
a. High Clouds- (cirro)
i. Cirrus – wispy
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ii. Cirrostratus - sheet like
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iii. Cirrocumulus - fish scales
5
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b. Middle Clouds - (alto)
i. Altostratus - prevent shadows
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ii. Altocumulus - long puffy strips or blotches
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c. Low clouds
i. Stratus - gray and cover entire sky
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ii. Stratocumulus - wide gray, puffy clouds
iii. Nimbostratus - Cover sky, wet looking, “fog”
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d. Vertical Clouds
i. Cumulus – pillowy
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ii. Cumulonimbus - anvil shaped, tall clouds,
produce tornadoes
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IV. Air Masses- (fig 27.8)
a. Convectional lifting –
warming air rises from “hot spots” followed by
sinking cooler air
i. Visualize a lava lamp
b. Orographic lifting - air that is pushed up by
a land mass
i. Warm dry air sinks on opposite side creating a
rain shadow
c. Frontal lifting - (Figs. 27-11 and 27-12)
i. Front - the contact zone between two air masses
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ii. Differences in temp., moisture and pressure
cause movement of air masses
iii. Cold front - cold into warm air mass
iv. Warm front - warm into cold
V. The Atmosphere
a. Atmospheric Pressure
i. Pressure exerted by air molecules because they
have weight
ii. Decreases with increasing elevation
iii. Composed of primarily Nitrogen and Oxygen
b. Layers of the Atmosphere
i. Thermosphere
1. 90 - 500 km
ii. Mesosphere
1. 50 - 90 km
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iii. Stratosphere
1. 16 - 50 km
2.
contains the ozone layer
3. 99% of atmosphere is below
35 km
iv. Troposphere
1. 16 km at the equator
2.
8 km at poles
3. commercial jets fly at the top of
troposphere to avoid weather
4.
90% of atmosphere’s air mass
5. all water vapor and clouds
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VI. Violent Weather
a. Thunderstorms i. Humid air rises cools and condenses
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ii. Lightning 1. falling water droplets bump into and rub
against one another
2.
cloud becomes electrically charged and
release as lightning
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iii. Thunder - lightning heats air up and it expands
so fast it breaks the sound barrier
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iv. Fun Facts
1. ~1800 thunderstorms in progress in
earth’s atmos.
2.
lightning strikes ~100 times every sec.
3. Claims more than 200 people/ yr.
b. Tornadoes – funnel cloud that has touched the
ground
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Oklahoma Tornado
Tornado
c. Hurricanes (Typhoons in the Pacific)
i. Winds up to 300 km/hr.
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ii. Caused by a long term supply of warm, moist air
iii. Lose power as they move onto land
Hurricane Rita
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Hurricane from Space Shuttle
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Hurricane Katrina
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Hurricane Dennis
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Hurricane X
Hurricane Wilma
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