Why Do We Have Weather?

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Why Do We Have Weather?
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WHY DO WE HAVE THE WEATHER ?

• Just think about it!
• Why is there wind? Why does it blow from one
  direction one day and another the next?
• Why is it rainy one day and dry the next?
• How come its cold in the winter?
• How can we have hail in the summer?
• What causes snow and freezing rain?

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If we were to pick one term to help explain why
we have weather, what do you think would be a
good word?

• You might pick heat or sun.but another good
  choice would be
• Convection

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After the atmosphere is warmed by radiation and
conduction, the heat is transferred throughout
the atmosphere by convection.

• Since warmed air has more space between the
  molecules, its less dense and rises
• Cooled air is more dense and tends to sink
• In general, air near the equator tends to rise
  and air near the poles tends to sink

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Take a look at this!
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Why do you think there is this band of clouds
near the equator?
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Did you figure it out?

• Warm, moist air in the topics rises
• Cold air can hold less moisture than warm air
• As the moist air rises, it condenses and forms
  clouds!

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Hadley Cells

• Caused by convection currents.
• Warm air near the equator rises
• Cold air near the poles sinks

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Consequences of Rotation the Coriolis Effect
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The Weather Highways

• The rotation of the earth creates the Coriolis
  effect.
• The Coriolis effect causes the air and water to
  be deflected to the West.
• This creates global weather highways.

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The Prevailing Westerlies

• Because of our latitude, most of our weather
  comes from the west
• Looking at the weather map, what type of weather
  might we expect?

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Combining Hadley Cells, the Coriolis Effect, and
Prevailing Westerlies gives you...

• Tradewinds
• Where do you think
• they got their name?
• Who were these winds
• particularly important to?

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Lets break for a short review

1. Transfer of heat in liquids or gases_____
2. _____ air is dense and tends to sink.
3. Cold air holds _____ moisture than warm air
4. The Coriolis effect causes the air and water to
   be deflected to the _____

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How did you do?

• 1. CONVECTION
• 2. COLD
• 3. LESS
• 4. RIGHT (WEST)

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Now What?

• Ok, so we know that the wind and weather move
  around on these highways and that warm air rises
  and cold air sinks.
• But why is it sunny one day, and rainy the next?

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Lets take another look at the weather map

• Notice that there are Hs and Ls on the map
• There are also blue lines with spikes and red
  lines with half circles

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High Pressure Areas

• When cooler air sinks and is warmed, the air can
  hold more moisture
• This usually means sunny and clear skies
• Winds tend to move clockwise around a high

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Low Pressure Areas

• When warm air rises and is cooled, the air cannot
  hold as much moisture
• Often, these areas are associated with
  precipitation and stormy weather
• Tornadoes and hurricanes can produce very low
  pressure readings.

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Fronts and Air Masses

• An air mass is a large body of air whose
  temperature and moisture are fairly similar at a
  given altitude
• Fronts are boundaries separating different air
  masses
• There are four different air masses that affect
  the United States

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The Air Masses

• cP( continental polar) cold, dry, stable
• cT( continental tropical) hot, dry, stable air
  aloft, unstable at the surface
• mP( maritime polar) cool, moist, unstable
• mT( maritime tropical) warm, moist, unstable

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This map shows the air mass source regions and
their paths
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Lets look at the different fronts and their
impact on weather

• Can you see the four different types of fronts on
  the map?

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Cold Fronts
This is the symbol for a cold front

• Cold air pushes under a warm air mass. Warm air
  rises quickly narrow bands of violent storms
  form

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Warm Front

• Warm air slides over departing cold air- large
  bands of precipitation form

This is the symbol on a map for a warm front
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Occluded Front
This is the weather map symbol for an occluded
front

• 2 air masses merge and force warm air between
  them to rise quickly. Strong winds and heavy
  precipitation will occur

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Stationary Front
This is the weather map symbol for a stationary
front

• Warm or cold front stops moving. Light wind and
  precipitation may occur across the front boundary

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Ready for a little quiz?

• Write your answers as we go
• Here we go!

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1.

• Winds in a low pressure system move _____ around
  the low

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2.

• What type of front can be found close to point D?

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3.

• Which of these fronts would you expect to have
  greater precipitation, but be short lived as the
  front passes?

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4.

• Give the name of the air mass that would have the
  following characteristics
• cool, moist, unstable

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5.That important weather word that refers to the
transfer of heat
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6.In general, air near the equator tends to_____
( rise or fall )
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7.

• It causes air and water to be deflected to the
  right north of the equator

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8.Which of the weather highways usuallycontrols
our weather
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9.

• Warm air holds ( more or less ) moisture than
  cold air

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10.

• If there is a big H on the weather map where you
  live, would you expect fair or stormy weather

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How did you do?

• 1. Counterclockwise 8.
  Westerlies
• 2. Cold 9.
  More
• 3. Cold 10.
  Fair
• 4. Maritime polar (mP)
• 5. Convection
• 6. Rise
• 7. Coriolis

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Thermometer

• A tool used to measure temperature
• How hot or cold it is outside
• Thermometers have different scales
• We measure in Celsius!

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Barometer

• A tool used to measure air pressure
• The weight of air pushing on the earths
  atmosphere

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Hygrometer

• A tool used to measure humidity
• How much water is in the air?
• Think hhumidity
• h hygrometer

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Anemometer

• A tool used to measure the wind speed
• How fast is the wind blowing?
• Think Ants move fast
• Anemometer how fast wind is moving

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Rain Gauge

• A tool used to measure the amount of rainfall

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Doppler Radar

• A type of radar used to locate precipitation,
  calculate its motion, and estimate its type.

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Satellite Imagery

• Satellite imagery consists of images of Earth
  collected by artificial satellites.
• Meteorologists use it to determine cloud coverage.

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Katie wants to measure the amount of moisture in
the air. She does not want the water in the air
to disorder her hair. What instrument should she
use?
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HYGROMETER!
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Mrs. Hartman plans to go out over the weekend on
her new sailboat. First, she must know how fast
the wind is blowing to see if its appropriate to
sail. What instrument should she use?
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ANEMOMETER!
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Mrs. Leab wants to make sure that she dresses
Baby Joseph correctly when she brings him to
visit us. In order for her to know the
temperature outside, what instrument should she
use?
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THERMOMETER!
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A meteorologist observes some cumulonimbus clouds
outside. He speculates that there is LOW air
pressure. What instrument should he use to
determine the air pressure?
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BAROMETER!
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Ryan is working on his Science Fair project. He
plans to measure the amount of rainfall that has
fallen in his neighborhood over the past two
weeks. What instrument should he use?
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RAIN GAUGE!