Transcript Chapter 38

Chapter 38
Weather
Humidity
Humidity is the measure of the water vapor in the
air. It is defined as the mass of water per volume
of air.
What is relative humidity? Why is it called
“relative”?
1.
2.
a.
b.
c.
d.
Amount of water vapor air can hold
Relative b/c it is compared to something else
75% humidity = air holds 75% of the moisture it could
hold at that temperature
50% - if the air can normally hold 6 gallons of water at
the temperature, how much would it be holding at 50%
humidity?
Air Saturation
When does air saturation occur?
4.
a.
b.
5.
6.
Something is saturated if it can’t hold anymore
Air saturation occurs when the air can’t hold
anymore water
Warm air can contain more water vapor
than cold air.
Air cools when it expands. This causes the
water in the air to move slower and
condensation occurs.
Clouds & Precipitation
7. How are clouds created?
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Air cools and moves slower
Molecules condense on particles in the sky
and create clouds
8. List the five forms of precipitation.
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Rain, sleet, snow, hail, mist
9. What causes fog?
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Condensation that occurs near the ground
Dew Point
10.
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What happens at the dew point?
Air cools & holds less water
Saturated air causes condensation to occur on
available surfaces = dew
Air Pressure, temperature, & density
are the key variables that control weather.
11.
Air Pressure
12.
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13.
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Define pressure.
Force exerted on an area
What is kinetic energy and how is it related
to air pressure.
Energy of movement
Faster molecules = more energy = harder
collisions = higher pressure
Heat Exchange
14. Explain how air density effects air
pressure.
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Denser air = more collisions = higher pressure
15. When heat is added to air its temperature,
pressure or both increase.
16. 3 Things Add Heat to Air
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Solar radiation
Moisture condensation
Contact with warm surface
Adiabatic Process
17. What is an adiabatic process?
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HEAT exchange = 0, Change in temperature
due to change in pressure
Air rises = Less pressure = air expands = colder
temperature
Air cools 10 degrees Celcius for every 1 km rise
18. Behavior of an Air Parcel
•Air Pressure on the balloon (or air parcel) decreases as you move up
in the atmosphere
•This creates less pressure outside the balloon
•Balloon expands
•Air inside the balloon cools off as it has more room to move
Rising Air
19. As rising air cools, its ability to hold water
decreases so the relative humidity of rising
air increases . If this rising air cools to its
dew point a cloud forms.
20. Condensation of water releases heat,
heats the air around it and slows the cooling
process.
Stable Air
21.
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How is a Chinook wind formed?
Cold air moving down a mountain is
compressed (moves closer together)
Causes the air to warm up
Created as air comes down Rocky Mountains
across the Great Plains
Temperature Inversions
Describe a
temperature
inversion.
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Air continues to rise
as long as it is
warmer and less
dense that the
surrounding air
Some conditions
cause cold air to sink
and warm air to rise
above it
The cold air remains
below because it is
less dense than the
air above it
Causes a
temperature inversion
Smog

What causes the
Los Angeles
smog?
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Cold air from
ocean trapped by
hot air from
Mojave Desert
Air can’t escape,
traps all the
pollutants and
causes a layer of
smog
CLOUDS
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1)
What are the three main types of
clouds? What is the pre-fix for each?
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High = cirro, above 6000 m
Medium = alto, 2000-6000 m
Low = strato, below 2000 m
Common Clouds
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Cumulus clouds: look like floating cotton
Cumulonimbus: dark clouds, usually mean a
storm
AIR MASSES
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5)
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Type of air mass determined by two things:
i) Surface air mass forms over (lower case letters)
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Maritime (m) or Continental (c)
ii)
Source region where air mass forms (upper case
letters)
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(a)
(a)
Arctic (A), Polar (P), or Tropical (T)
6) What are the 6 possible air masses?
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mA – cool, moist, unstable
cA – cold, dry stable
mP – cool, moist, unstable
cP – cold, dry, stable
mT – warm, moist; usually unstable
cT – hot, dry, stable or unstable
LIFTING
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1)
Different weather occurs when two
different air masses meet.
2)
What cause convectional lifting?
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Unequal heating of earth
Convection currents create lifting
3)
Orographic lifting is lifting upward over
an obstacle
Draw what happens due to orographic
lifting
FRONTS
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10)
What is a front? What type of weather do
they typically bring?
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Contact zone between two different air masses
Wind, Clouds, Rain, and Storms
11)
Frontal lifting occurs due to a difference in
temperature, moisture, and pressure.
12)What is the difference between a warm and cold
front?
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Cold = cold air mass moves into an area with a nonmoving warm air mass
Warm = warm air moves into cold air
Less obvious, light
to moderate
rain/snow, air
warm behind front,
clouds scatter
WARM FRONT
COLD FRONT
High cirrus
clouds, drop in
temperature, and
drop in pressure
before,thundersto
rms, air cools
behind front
VIOLENT WEATHER
a)
Thunderstorms – humid air rises, cools,
and condenses into single cumulus cloud
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Rising warm air continues to feed the cloud
Rain falls, takes cold air with it
Creates lightning and thunder
b) Tornadoes
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Winds rotating over a large area speed up
when you decrease the area (figure skater)
Funnel shaped cloud from a cumulonimbus cloud
Only called a tornado when it touches down
Tornado Alley – stretches from northern Texas through
Oklahoma, Kansas, and Missouri
c) Hurricanes
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Air and water temperatures become equal
Increase in moisture and temperature of air
causes strong vertical wind
Causes rising air to tail in and spiral
Grows as more air rises