Changes in Weather

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Section 8-2

• Changes in Weather

http//www.sciences.gc.ca/8E2607CB-F2D8-40C5-B923-
971D0F6875C8/web_trans_changes2.jpg
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Air Masses

• Changes in weather are caused by the development
  and movement of large air masses
• Air masses are constantly moving and swirling
  over the surface of earth
• During different times of the year different air
  masses dominate the weather

http//videos.howstuffworks.com/hsw/23681-weather-
types-of-air-masses-video.htm
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• Air Mass
• a large body of air where temperature and
  moisture content is similar

• Examples
• One that develops over land is dry compared to
  one that develops over water
• One that develops near the equator is warmer than
  one that develops at a higher latitude

http//www.weatherquestions.com/air_masses_AMSU.jp
g
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Continental Arctic (cA)
http//www.uwsp.edu/geo/faculty/ritter/maps/air_ma
sses_2.jpg

• very cold very dry

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Continental Antarctic (cAA)
http//www.uwsp.edu/geo/faculty/ritter/images/maps
/atmosphere/air_masses_small.jpg

• very cold very dry
• 60 and 90 south latitude.   

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Continental Polar (cP) air
http//www.csulb.edu/rodrigue/geog140/airmassbjer
knes.jpg
cold dry Typically a stable or conditionally
stable mass of air.
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Continental Tropical (cT)
http//www.fas.org/irp/imint/docs/rst/Sect14/air_m
asses_2.jpg
warm dry Major source regions are the great
deserts of the Earth such as the Sahara, Arabian,
and Australian.
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Maritime Equatorial (mE)
http//www.dask.org.tr/english/want_to_know/meteor
ology/air_masses/air_masses_2-new.jpg
very warm very moist
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Maritime Polar (mP) air
http//www.dask.org.tr/english/want_to_know/meteor
ology/air_masses/air_masses_2-new.jpg

• cool moist
• Brings mild weather to coastal locations.
  Maritime polar air is warmer than continental
  polar air in the winter as the surface
  temperature of the ocean is higher.

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Maritime Tropical (mT) air
http//www.uwsp.edu/geO/faculty/ritter/maps/air_ma
sses_2.jpg
warm moist Responsible for much of the
precipitation east of the Rocky mountains in the
United States.
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• Maritime Tropical Air Masses
• warm temperatures and rich in moisture
• originate over the warm waters of the tropics
  and Gulf of Mexico, where heat and moisture
  are transferred to the overlying air from the
  waters below
• northward movement of tropical air masses
  transports warm moist air into the United States,
  increasing the potential for precipitation        
                         

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Air Masses of North America
http//www.fas.org/irp/imint/docs/rst/Sect14/airma
sses_schem.jpg
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Fronts

• When an air mass moves and collides with another
  air mass, a boundary forms between the two air
  masses.

http//videos.howstuffworks.com/hsw/23683-weather-
air-mass-boundaries-fronts-video.htm
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Warm Front
http//upload.wikimedia.org/wikipedia/commons/thum
b/1/1e/Weather_fronts.svg/500px-Weather_fronts.svg
.png

• Warm air rises and meets a cold air mass so
  temperature falls and forms precipitation.

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A warm front is a leading edge of warmer air.
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Cold Front

• A cold air mass invades a warm air mass forcing
  the warm air upward.

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• cold front is an area of cooler air, not cold air
• possible to have cold fronts in the summer
• cold front often triggers storms

http//www.ecn.ac.uk/Education/cold_fronts.htm
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Comparing Warm and Cold Fronts
http//www.classzone.com/books/earth_science/terc/
content/visualizations/es2002/es2002page01.cfm?cha
pter_novisualization
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Stationary Front

• - A stationary front is an air mass that is not
  moving
• - Cold air mass meets warm air mass and doesnt
  move

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Occluded Front

• Two cold air masses meet and force a warm air
  mass up in between them.

http//www.windows.ucar.edu/earth/Atmosphere/image
s/occluded_front_sm.jpg
http//www.physicalgeography.net/fundamentals/imag
es/occludedfront.GIF
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occluded front - occurs when a faster moving cold
front passes under a warm front, and catches up
to another cold front
http//www.cartage.org.lb/en/themes/Sciences/Earth
science/Hydrology/Meteorology/AirMasses/Fronts/Occ
ludedFront/ofdef1.gif
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Pressure Systems

• Difference in pressure affect the weather

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High Pressure

• usually clear weather, air molecules are densely
  packed
• as cool, dense air sinks it becomes warmer
• when it warms, it can hold more moisture
• droplets of water from clouds evaporate into
  warmer air

http//www.animationfactory.com/en/search/close-up
.html?oid4950964s1sc1st663qhigh20pressu
respage1hoid34f244b0ec38fbac1aa13ac92581657b
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http//www.whistlerweather.org/uploaded_images/P80
10089-769007.JPG
http//www.whistlerweather.org/uploaded_images/P80
10089-769007.JPG
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Low Pressure

• usually cloudy weather, air molecules are less
  densely packed
• as warm, less dense air rises, it cools
• cold air cant hold as much moisture, so water
  droplets become clouds.
• causes most of the weather changes in the US

http//www.animationfactory.com/en/search/close-up
.html?oid4950656s1sc1st195qlow20pressur
espage1hoid8248cdcf4d0c5d164d55a4ea816297ec
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http//z.about.com/d/weather/1/0/l/-/-/-/precipsym
bols.gif
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Wind Barbs Show Wind Direction and Speed in Knots

• Barbs point to direction wind is coming from. (1
  Knot 1.15 mph)

http//www.scalloway.org.uk/images/knots.gif
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http//www.rap.ucar.edu/weather/info/wind_barb.gif
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Cloud Cover in a Weather Station Model

• Weather station model symbols used to indicate
  cloud cover.
• National Science Foundation

http//z.about.com/d/weather/1/0/R/-/-/-/cloudcove
r.gif
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Weather Map Symbol
http//www.hpc.ncep.noaa.gov/images/plotstation.gi
f
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Weather Map Symbols
http//dstreme.comet.ucar.edu/extras/wxsym2.html
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Thermometers

• Measures temperature

http//www.oregongadgets.com/images/prods/RGR126p.
gif
http//img.alibaba.com/photo/50571760/Sell_Garden_
Thermometers.jpg
http//gidesigns.net/garden-decor/files/images_bac
kup/d_747.jpg
http//www.world-shop1.com/images/medical/digital
20thermometers20EBT-1.jpg
http//www.mercuryinyourhome.com/images/DigitalThe
rmometers.jpg
http//www.dzwholesale.com/Galileo_Thermometer_38c
m.jpg
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Barometers

• Measures atmospheric pressure

http//www.treasurequestshoppe.com/images/Tabletop
Weatherglass.jpg
http//img.nauticexpo.com/images_ne/photo-g/digita
l-barometer-50659.jpg
http//www.weathershop.co.za/Dialbarometers/45_100
2pic.jpg
http//www.asiuk.net/rb5.jpg
http//cart.clockparts.com/images/W73GBI.jpg
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Satellites

• Record air currents and cloud formation

http//www.thorntonweather.com/blog/wp-content/upl
oads/2008/12/goes-r.jpg
http//www.noaanews.noaa.gov/stories2005/images/no
aa-n.jpg
http//z.about.com/d/weather/1/0/q/0/-/-/TRMM_INST
.gif
http//www.newscientist.com/data/images/ns/cms/dn8
340/dn8340-1_590.jpg
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Psychrometer

• Measures relative humidity

http//www.greenhousemegastore.com/images/sling-ps
ychrometer-100.jpg
http//ecx.images-amazon.com/images/I/5176E1S7H2L.
_SL500_AA280_.jpg
http//www.novalynx.com/225-sam.html
http//www.physicalgeography.net/fundamentals/imag
es/sling_psychrometer.jpg
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Radar

• Is used to detect raindrops and ice particles up
  to 400 kilometers away.

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Radar Intensity Colors on a Weather Map

• Radar Echo Intensity shows the amount of
  precipitation in an area by assigned a series of
  colors to indicate heavy or light precipitation
  including hail, rain, and snow.
• NOAA National Weather Service

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Bibliography

• "Cold Fronts." Environmental Change Network (ECN)
  Home Page. The United Kingdom Environmental
  Change Network. 17 Mar. 2009 lthttp//www.ecn.ac.uk
  /Education/cold_fronts.htmgt.
• Glencoe/McGraw-Hill Team. Teacher's for Use with
  Science Interactions Course 3. 3rd ed. New York
  Glencoe/McGraw-Hill, 1998. 80.
• Opie, Alexandra. "Precipitation." All About Us.
  Canterbury Broad Oak Environmental Education
  Centre. 09 Mar. 2009 lthttp//www.econet.org.uk/wea
  ther/ppt.htmlgt.
• Ritter, Michael. "Air Masses." University of
  Wisconsin-Stevens Point. University of
  Wisconsin-Stevens Point. 22 Mar. 2009
  lthttp//www.uwsp.edu/geO/faculty/ritter/maps/air_m
  asses.
• "The Water Cycle." Kidzone - Fun Facts for Kids!
  1998-2009. Concordia University Saint Paul. 09
  Mar. 2009 lthttp//www.kidzone.ws/water/gt.