Meteorology The study of WEATHER

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Meteorology- The study of WEATHER

• The study of this unit will include-
• Composition and structure of the atmosphere
• Pressure and its affects on weather
• Energys role in the atmosphere
• Winds
• Water in the atmosphere
• Air masses and Fronts
• Climate

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The Atmosphere-The Gases around You
Atmosphere is also made up of liquids and solids
invisible to the naked eye.
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Why do we need to care about each of these gases?

• Nitrogen- essential to living things b/c it
  makes up our DNA and proteins that compose us.

• Oxygen- we need it for cellular respiration
  (chemical rx. That makes energy for us) also
  need it to make fire ozone is made of oxygen

• Carbon dioxide- plants need it for
  photosynthesis and we need them in the food chain

• Water vapor- is important in weather. Produces
  clouds and precipitation

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Layers of the Atmosphere(Our protective blanket)
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Key Terms for Each Layer

• Troposphere- lowest, heaviest,weather occurs
  here
• Stratosphere- has ozone, greenhouse effect,
  protects us from UV radiation
• Mesosphere-coldest, protects earth from
  meteoroids
• Thermosphere-hottest, 2 layers-ionosphere
  (important in communication) and
  exosphere-satellites orbit here, gases escape
  here

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Air Pressure

• Air like anything that is made of atoms has mass
  which allows it to also have other properties
  like density and pressure.

• Air exerts a pressure on us b/c of the weight of
  the air on top of us.

• Doesnt seem to weigh much b/c it is a gas, but
  there is about 20 miles of air stacked on your
  head. (about 100 lbs of force on your head)

• Air pushes in all directions (Pascals Law).
  This is why air pressure doesnt crush objects.

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Understanding Air Pressure

• Altitude and Pressure-
• Air actually gets thinner as you go up or
• Increase in altitude decrease in air pressure
  and vice versa.

• Actual atmospheric pressure is 14.7 lbs/square
  inch at sea level.

Cooking at Altitude
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Understanding Air Pressure

• Pressure is measured with barometers
• 2 types aneroid and mercury
• Units of measurement inches of mercury or
  millibars

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Air Pressure

• Changes in air pressure help forecasters predict
  how the weather will change. Use lines called
  isobars to draw out and connect areas with the
  same pressure. They look for patterns. weather.
  Areas with H pressure tend to have fair weather.
  Areas with L pressure tend to have stormy weather.

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So what does PRESSURE have to do with WEATHER?

• Pressure in the atm. ? with ? height (altitude)

• ? in air pressure ? temperature

• Change in temperature change in amount of water
  vapor that air can support

• Winds are caused by differences in air pressure.
  (Flows from H to L)

• Falling air pressure storm approaching
• Rising air pressure weather is clearing

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Energys Role in Weather
The earths EXTERNAL energy source is the
SUN. This energy travels to Earth as
ELECTROMAGNETIC WAVES (can travel thru empty
space) This type of energy transfer is called
RADIATION Types of electromagnetic waves of
energy Visible light, infrared radiation, UV
radiation Classified by wavelength.
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What happens to this energy?
Greenhouse effect!
This energy is absorbed and reflected differently
all over the Earth causing unequal heating of the
Earth.
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Winds and Energy

• Winds are caused by difference in air pressure.
• What causes differences in air pressure?
• -Unequal heating of the earth because of uneven
  absorption and reflection of radiation
• Cooler, dense air (H pressure) flows underneath
  warmer, less dense air (L pressure) forces warm
  air to rise.
• Winds described by direction and speed
• Instruments wind vane (direction) and anemometer
  (speed)

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Local Winds

• Two basic types of winds
• Local and global
• Important facts for LOCAL Winds
• Blow over short distances
• Sun heats land (s) faster than water (l) day air
  over land warmer than air over watercool air
  blows inland from water and is called SEA or
  LAKE breeze.
• At night, land (s) cools more quickly than water
  (l), so air over land is cooler than air over
  water cool land air blows toward water and is
  called LAND breeze.

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Global Winds
Winds that blow steadily from specific directions
for long distances. Equator- warm air
rising Poles- cold air sinking This causes winds
to blow from poles to equator. Earth is rotating,
so winds dont blow in a straight path, they are
curved (Coriolis effect). In N. H. curve to
right In S. H. curve to left
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The Major Wind Patterns
B/C of Coriolis Effect and other factors there
are calm areas and wind belts around the
Earth. Doldrums/Horse Latitudes Trade
Winds Prevailing Westerlies Polar Easterlies Jet
Stream (High speed winds, 10 km, blow from W to E)
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Water and the Atmosphere
Water exist in all 3 states of matter in the
atmosphere Solid- snow, hail, ice
particles Liquid- rain or cloud droplets Gas-
invisible water vapor Water can change from one
state to another depending upon the addition or
the subtraction of energy. Water vapor is spread
throughout the troposphere by convection currents
and winds.

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Water Cycle

• The movement between states of matter for water
  is called the water cycle.

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Humidity

• The capacity of air for holding water vapor
  depends on the temperature of the air. The
  warmer the air, the more water vapor it can hold.
• Specific humidity- the amount of water vapor
  actually present
• Hot, humid day 20 g/kg
• Cold, winter day 5 g/kg
• When spec. humidity the airs capacity for
  holding vapor
• Saturated
• Relative humidity compares the actual amount of
  water vapor in the air with the maximum amount of
  water vapor the air can hold at that temperature.
  Specific humidity/capacity X 100

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Forms of Condensation

• Once atmosphere has reached its capacity, as the
  temperature continues to cool, all the water
  vapor above its capacity condenses.
• Dew- water vapor condenses on grass (dew
  point-temp. at which saturation occurs)
• Frost- water vapor condenses on surfaces as a
  solid b/c surface is below 0 degrees Celsius
• Fog- a surface layer of air a few hundred meters
  thick cooled below dew point and water vapor
  condenses throughout the entire layer, tend to
  stay suspended. 2 types-radiation fog and
  advection fog
• Hail- irregular spheres or lumps of circular ice
• Sleet- frozen raindrops

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Clouds

• The Origin of Clouds-
• Clouds form when air above the surface cools
  below its dew point.
• 4 families of clouds
• High clouds- 7000 13000 m
• Middle clouds- 2000 7000 m
• Low clouds- 500-2000 m
• Vertical development- 500-13000 m
• 3 main cloud types
• Shaped by air movements-
• CIRRUS ( thin, feathery, tufted, high)
• STRATUS ( low sheets or layers),
• CUMULUS ( vertically rising air currents, thick,
  puffy)
• Prefixes alto (high) and nimbus (rain cloud)

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Cloud Types
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Fronts

• Fronts are some of the basic building blocks of
  weather systems. Fronts occur where two large air
  masses collide at the earth's surface. Each air
  mass has a different temperature associated with
  it. Fronts are caused by winds moving one air
  mass away from its birthplace. Due to the
  collision of air masses, fronts are usually
  associated with some form of precipitation.
  Thunderstorms, tornados and other severe weather
  can occur with fronts.
• Four basic types
• Warm
• Cold
• Stationary
• Occluded

When a meteorologist talks about fronts on the
news, the weather map he/she shows usually has
all these weird lines on it. These symbols
signify what kind of front he's/shes talking
about. The image beside explains which symbol is
associated with which front.
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Warm Fronts

• Warm fronts occur when warm air replaces cold air
  by sliding over it. Altocumulus clouds form and
  may be associated with rain, snow, or sleet.
  Temperatures may warm slightly. Winds are usually
  gentle with this kind of front.
•  

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Cold Fronts

• Cold fronts occur when heavy cold air displaces
  lighter warm air, pushing it upward. Cumulus
  clouds form and usually grow into thunderstorms.
  Temperatures drop anywhere from 5 degrees to 15.
  Winds become gusty and erratic. Rain, snow,
  sleet, and hail can occur with a cold front.

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Stationary Front

• Stationary fronts occur when neither warm nor
  cold air advances. The two air masses reach a
  stalemate. That is what stationary means - that
  neither front is moving. These type of conditions
  can last for days, producing nothing but
  Altocumulus clouds. Temperatures remain stagnant
  and winds are gentle to nil.

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Occluded Front

• Occluded fronts occur when cold air is replacing
  cool air or vice versa at the surface, with warm
  air above. These types of fronts are usually
  associated with rain or snow and cumulus clouds.
  Temperature fluctuations are small and winds are
  gentle.

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Thunderstorm Formation
Most thunderstorms form by a special cycle. This
cycle has three stages the Cumulus Stage, Mature
Thunderstorm Stage, and Dissipating Stage.
Cumulus Stage The sun heats the earth's surface
during the day. The heat on the surface and warms
the air around it. Since warm air is lighter than
cool air, it starts to rise (known as an
updraft). If the air is moist, then the warm air
condenses into a cumulus cloud. The cloud will
continue to grow as long as warm air below it
continues to rise.
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Thunderstorm Formation
Mature Stage When the cumulus cloud becomes very
large, the water in it become large and heavy.
Raindrops start to fall through the cloud when
the rising air can no longer hold them up.
Meanwhile, cool dry air starts to enter the
cloud. Because cool air is heavier than warm air,
it starts to descend in the cloud (known as a
downdraft). The downdraft pulls the heavy water
downward, making rain. This cloud has become a
cumulonimbus cloud because it has an updraft, a
downdraft, and rain. Lightning and thunder start
to occur, as well as heavy rain. The cumulonimbus
is now a thunderstorm cell.
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Thunderstorm Formation
Dissipating Stage After about 30 minutes, the
thunderstorm begins to dissipate. This occurs
when the downdrafts in the cloud begins to
dominate over the updraft. Since warm moist air
can no longer rise, cloud droplets can no longer
form. The storm dies out with light rain as the
cloud disappears from bottom to top. The whole
process takes about one hour for an ordinary
thunderstorm.
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Lightning and Thunder
Lightning is the most spectacular element of a
thunderstorm. In fact it is how thunderstorms got
their name. Wait a minute, what does thunder have
to do with lightning? Well, lightning causes
thunder. Lightning is a giant spark. A single
stroke of lightning can heat the air around it to
30,000 degrees Celsius (54,000 degrees
Fahrenheit)! This extreme heating causes the air
to expand at an explosive rate. The expansion
creates a shock wave that turns into a booming
sound wave, better known as thunder. Thus the
name thunderstorm.
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Lightning Formation
The sky is filled with electric charge. In a
calm sky, the and - charges are evenly
interspersed throughout the atmosphere.
Therefore, a calm sky has a neutral charge.
Inside a thunderstorm, electric charge is spread
out differently. A thunderstorm consists of ice
crystals and hailstones. The ice crystals have a
charge, while the hailstones have a - charge.
The ice crystals are pushed to the top of the
thunderstorm cloud by an updraft. Meanwhile, the
hailstones are pushed to the bottom of the
thunderstorm by its downdraft. Thus, the
thunderstorm's and - charges are separated into
two levels the charge at the top and the -
charge at the bottom.
Charges before a thunderstorm is in full effect.
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Lightning Formation
During a thunderstorm, the Earth's surface has a
charge. Because opposites attract, the - charge
at the bottom of the thunder cloud wants to link
up with the charge of the Earth's surface.
Once the - charge at the bottom of the cloud
gets large enough to overcome air resistance, a
flow of - charge rushes toward the earth. This is
known as a stepped leader or streamer. The
charges of the Earth are attracted to this
streamer, so a flow of charge moves into the
air. When the streamer and the charge from the
earth meet, a strong electric current carries
charge up into the cloud. This electric current
is known as the return stroke of lightning and is
visible to the human eye.
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Sound Waves vs. Light Waves
You see a flash of lightning across the night
sky. Five seconds later, your hear the rumble of
thunder. If lightning and thunder come from the
same source, then why don't they occur at the
same time? Actually, they do occur at the same
time. The time difference that you sense is due
to the way sound and light travel. Light travels
extremely fast (300,000,000 m/s). In fact, it is
faster than anything else. Sound travels at a
measly 343 m/s through air. Therefore we can see
light in an instant, but it takes a while to hear
thunder. Sound has another disadvantage because
it tends to bounce off molecules in the air. This
makes the sound travel in all different
directions. The further away the source of the
sound is, the more the sound gets distorted.
Therefore, when you hear rumbling thunder, the
lightning bolt was far away. When you hear a
crack or boom of thunder, the lightning bolt is
close to you (lt100 m).
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Tornadoes

Tornadoes form from severe thunderstorms. They
have a very high energy density which means that
they affect a small area but are very destructive
to that area. They also don't last very long
which makes it hard to learn about them. Since
they're hard to study, they're also hard to
forecast. Tornadoes can occur anywhere in the
world. About 75 of them happen in the United
States, most in an area know as Tornado Alley.
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Tornado Formation
Tornado begins in a severe thunderstorm called a
supercell. A supercell can last longer than a
regular thunderstorm. The same property that
keeps the storm going also produces most
tornadoes. The wind coming into the storm starts
to swirl and forms a funnel. The air in the
funnel spins faster and faster and creates a very
low pressure area which sucks more air (and
possibly objects) into it. Tornadoes can form
any time during the year, but most form in May.
But, more severe ones form earlier because the
most damage is caused in April. Most tornadoes
spin cyclonically (counter clockwise), but a few
have been determined to spin anticyclonically
(clockwise). How do tornadoes form?
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Hurricane formation
Hurricanes are violent storms which begin in the
tropics near the equator. They can't form right
on the equator because there is no Coriolis Force
right on the equator. The Coriolis Force causes
the hurricane to spin just like it causes water
to spin when it goes down a drain. Hurricanes
even spin the same direction as the water!
Hurricanes need a lot of energy and they get the
energy from the ocean. The warm water and warm
air near the surface help to cause hurricanes to
form. Once they form, hurricanes take energy from
the water to get stronger. While a hurricane is
over warm water it will continue to grow. If it
travels over land it will start to weaken and
eventually end. This is why mainly coastal areas
are affected by hurricanes.
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Hurricanes
They are the most powerful of all weather
systems. Hurricanes form over the warm tropical
water in ocean and die down when they move over
land. Meteorologists try to forecast where and
when the center of the storm, the eye, will reach
land in order to warn people about the damage
caused by the strong winds, heavy rain, and storm
surge. Hurricanes have been given alternating
male and female names since 1979. These names
change every year. Hurricanes may form anytime
during the year, but they are most likely to form
between June 1st and November 30th this is
hurricane season. Global warming causes stronger
storms? As global warming causes oceans to
become warmer, and more moisture is held in the
atmosphere, the intensity of hurricanes and the
amount of rain they produce will likely increase,
according to NCAR scientist Kevin Trenberth and
others. There is strong evidence that global
warming has been increasing the intensity of
hurricanes for over the past few decades.