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WEATHER SYSTEMS
Team Leader:
Bob Holzer
Writer:
John Watson
Editor:
CHAOS Communications
Producer:
Michele Boniface
Content Reviewers:
Donna Matovinovic
Stella Shrum
Produced by ACCESS The Education Station
© 1997 Alberta Education
Published & Distributed by…
AGC/UNITED LEARNING
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Website: http://www.agcunitedlearning.com
E-Mail: [email protected]
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WEATHER SYSTEMS
Teacher’s Guide
Table of Contents
Introduction ............................................................1
Program Summary ................................................1
Links to Curriculum Standards ...........................1
Pre-Test ....................................................................2
Teacher Preparation/Instructional Notes ..........2
Student Objectives .................................................3
Student Preparation ..............................................3
Blackline Masters ...................................................4
Answer Key ............................................................5
Script of Video Narration ................................... 11
This video is closed captioned
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right to reproduce or duplicate, in whole or in part, this
teacher's guide and the blackline master handouts that accompany it for the purpose of teaching in conjunction with this
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INTRODUCTION
This Teacher’s Guide accompanies Program Eight,
“Weather Systems,” from the Simply Science series.
Simply Science is a series of twenty-five science programs
for high school students. These instructional programs use
practical applications as context to the interdisciplinary concept development emphasizing the connections among science, technology, and society. This comprehensive
Teacher’s Guide and accompanying blackline master activity sheets provide extended practice and additional learning opportunities.
PROGRAM SUMMARY
“Weather Systems” investigates the factors that influence
weather around the globe. We start with the heating of the
atmosphere and the oceans, then look at how this contributes to air and water currents around the globe. We also
examine how heating air causes thunderstorms, hail and
tornadoes.
LINKS TO CURRICULUM STANDARDS
“Weather Systems” correlates with the following National
Science Education Standards for grades 9-12:
Physical Science: Conservation of energy and the increase
in disorder
• Everything tends to become less organized and less orderly over time. Thus, in all energy transfers, the overall
effect is that the energy is spread out uniformly. Examples
are the transfer of energy from hotter to cooler objects by
conduction, radiation, or convection and the warming of
our surroundings when we burn fuels.
Earth and Space Science: Energy in the system
• Heating of earth's surface and atmosphere by the sun
drives convection within the atmosphere and oceans, producing winds and ocean currents.
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• Global climate is determined by energy transfers from
the sun at and near the earth's surface. This energy transfer is influenced by dynamic processes such as cloud cover
and the earth's rotation, and static conditions such as the
position of mountain ranges and oceans.
Earth and Space Science: Geochemical cycles
• Movement of matter between reservoirs is driven by the
earth's internal and external sources of energy. These movements are often accompanied by a change in the physical
and chemical properties of the matter. Carbon, for example,
occurs in carbonate rocks such as limestone, in the atmosphere as carbon dioxide gas, in water as dissolved carbon
dioxide, and in all organisms as complex molecules that
control the chemistry of life.
PRE-TEST
A Pre-Test is included with the Blackline Masters for this
program. It is meant to be administered before the video
and its ensuing activities are used. This assessment tool
allows you to gauge student comprehension of the Objectives before completing the lesson; its results may be contrasted with those of the Post-Test, also included herein, to
assess comprehension of the Objectives after completing
the lesson.
TEACHER PREPARATION/INSTRUCTIONAL NOTES
Before presenting this lesson to your students we suggest
that you preview the video and review this guide, and the
accompanying blackline master activities in order to familiarize yourself with their content.
As you review the materials presented in this guide, you
may find it necessary to make some changes, additions, or
deletions to meet the specific needs of your class. We encourage you to do so, for only by tailoring this program to
your class will they obtain the maximum instructional ben6
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efits afforded by the materials.
It is also suggested that the video presentation take place
before the entire group under your supervision. The lesson activities grow out of the context of the video, therefore, the presentation should be a common experience for
all students.
STUDENT OBJECTIVES
After viewing the video and participating in the follow-up
activities, students will be able to:
• Explain how uneven heating of Earth affects wind
and water currents.
• Define air mass and front.
• Explain the process that results in a thunderstorm.
• Explain why some thunderstorms result in hail.
• Plan an experiment to investigate the heating of the
atmosphere due to solar radiation.
• Predict wind direction using isobars on a weather
map.
• Describe the limits on current technology in predicting weather.
STUDENT PREPARATION
This video is one of a series. Before students view this program and complete the follow-up activities, they should
be able to:
1. Describe the difference between weather and climate.
Weather is a description of the state of the atmosphere, including
winds, precipitation, clouds, air pressure, storms and temperature. Climate is a description of the long-term weather patterns
in a specific area.
2. List some things you expect to observe during a thunderstorm.
Rain, wind, thunder, lightning and a change in air temperature
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are common during thunderstorms
3. Explain why warm air rises.
Air expands as it warms so there are fewer air molecules in the
same amount of space. That means warm air is less dense than
cool air, and less dense matter floats on more dense matter.
If students have difficulty with any of the items, you should
review the concepts in reference materials before viewing
the video.
BLACKLINE MASTERS
The following blackline master activity sheets are included
with this guide. Duplicate and distribute those you wish to
use. An Answer Key appears on pages 5-9.
(1.) Blackline Master #1: Pre-Test is to be given to your
students prior to viewing the video to assess their prior
knowledge of the topic. It may be contrasted to Blackline
Master #7: Post-Test to gauge student comprehension of
the Objectives after the lesson has been completed.
(2.) Blackline Master #2: Glossary is a list of terms from
the video. Students may find this handout helpful when
completing the activities which accompany this lesson, as
well as for preparation for the Post-Test.
(3.) Blackline Master #3: The Global Picture: Air Currents examines such phenomena as convection currents,
polar easterlies, and the uneven heating of the earth by the
sun.
(4.) Blackline Masters #4a-4b: The Global Picture: Water
Currents explores the effects water and water temperature can have on weather. Students will need graph paper
to complete the exercises.
(5.) Blackline Master #5: Predicting the Unpredictable
looks at weather prediction.
(6.) Blackline Master #6: Storms examines thunderstorms.
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(7.) Blackline Master #7: Prairie Weather examines how
fronts affect the local weather.
(8.) Blackline Masters #8a-8d: Post-Test is an assessment
tool to be used after the video and follow-up activities have
been completed. The test is based directly on the Student
Objectives for this program and the National Science Education Standards for grades 9-12.
ANSWER KEY
Blackline Master #1: Pre-Test
1.F
2.T
3.F
4.T
5.F
6.T
7.T
8.F
9.T
10.F
Blackline Masters #3-7
Note that some of these questions have more than one
possible answer.
1. The equator receives a great deal of solar energy. A
lot of heat is transferred to the atmosphere, which
expands and rises.
2. Polar easterlies blow from the east.
3. Solar radiation which reaches the surface of Earth
near the poles is spread over a much greater area than
the radiation which reaches the equator.
4. The high specific heat capacity of water causes large
bodies of water to moderate air temperature near
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them. They are slow to heat up on hot days, and slow
to cool down on cold days. As a result, large bodies
of water cool the air on hot days and warm it on cold
days.
6. Both temperature graphs peak during the same
month. The precipitation graphs are almost the exact
opposite of one another. Calgary receives the most
precipitation during July and August, the two driest
months for Vancouver. Vancouver receives almost
three times the quantity of precipitation that Calgary
receives. Calgary also has a lower average temperature than Vancouver.
7. The major differences are that Vancouver is located on
the coast of the Pacific Ocean and Calgary is located
on the edge of the prairies. Also, Vancouver is on the
rainy side of the coastal mountains and Calgary is on
the dry side of the Rockies. The latitude difference
likely has very little effect on the climate difference.
8. One possible design:
Use two identical two-litre pop bottles and add an
equal quantity of dry
sand to both. To one container add 100 mL of water.
Close the containers with cotton wool and insert a
thermometer through the wool into the centre of the
bottle. Place the containers in a window in direct
sunlight. Measure the temperature every 10 minutes
for one hour.
9. Calgary, Chicago and Halifax have an approaching
warm front.
10. As the cool air pushes into the warm air (producing
the cold front) the warm air is pushed away, producing a warm front.
11. Both Vancouver and Denver can expect severe storms
as cold fronts approach.
12. Thunderstorms get started with the rapidly rising air
that results from daytime heating of the ground.
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13.
14. As air rises it cools; first water condenses, then it
freezes. Strong updrafts hold the ice crystals aloft
while they grow larger and form hail, which eventually falls.
15. The energy that vaporized the water
is converted to thermal energy when the water condenses. This thermal energy adds to the energy of the
thunderstorm.
16. Compare your predictions to your observations.
17. The prevailing winds across most of southern Canada
are westerlies, so expect pressures systems there to
move towards the east. In the far north, polar
easterlies might be predicted to drive pressure systems to the west.
18. The high pressure system north of Toronto is likely
keeping the skies clear and the temperature warm.
Blackline Masters #8a-8d: Post-Test
Multiple Choice
1.
b.
warm fronts
2.
d.
prevailing winds
3.
a.
near the equator
4.
b.
temperate zones
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Long Answer
1.
tilt of Earth axis to the plane of the orbit around
the sun
2.
jet streams
3.
lines of equal pressure
4.
The warm air at the equator rises, reducing the
pressure at the surface. Air from either side of the
equator replaces the ascended air, creating
convection currents. The air cools in the upper
atmosphere and sinks down in regions north and
south of the equator, increasing the pressure at the
surface.
5.
winds; ocean currents
6.
Warm moist air rising rapidly meeting cooler air
above. This leads to water vapor condesing and
the beginning of a cloud. This build-up continues
as more warm air rises until a towering cloud
exists reaching 10 km above the surface. The top
of this cloud consists of ice crystals.
7.
updraft downdraft
8.
The streams of cold and warm air of the
downdraft-updraft combination passing each
other produce electrically charged particle, similar
to the electric charge separation that takes place
when you rub a balloon on your hair. The top of
the cloud becomes positively charged and the
bottom negative.
9.
10.
The air has had most of its moisture removed
traversing the various mountain ranges before coming to
the Rocky Mountains, thus it is very dry. As the air mass
descends it is compressed at the lower altitudes which
increases the temperature.
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11.
12.
13.
14.
15.
16.
17.
Pressure increases the temperature of a gas (air),
warm air can hold more moisture in the vapor
state. Therefore clouds don’t form.
The ice crystals from the top of a thunder cloud
fall due to gravity, normally they melt as they
reach lower altitudes and fall as rain drops.
However, sometimes they are caught in the up
draft before they melt and carried to the top again.
On the way up they gain more moisture which
freezes, adding another layer of ice. Then they fall
again. This process repeated several times leads to
hail stone forming. Eventually the hail stone are
so large they fall to the ground.
large bodies of water; large land masses; mountain
ranges; arge areas of forests; distance from the
equator
precipitation; average daily temperature
Climate - long-term, general weather trends in a
certain geographic region
Weather - short-term conditions, temperature,
wind speed and direction, precipitation, air
pressure, humidity
a warm air mass holds more moisture than a cold
one ; a cold air mass is more dense than a warm
air mass
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SCRIPT OF NARRATION
DANA: THE WORLD’S MOST ADVANCED TECHNOLOGY CAN’T
CONTROL IT. TODAY’S LAUNCH HAS BEEN POSTPONED DUE
TO WEATHER CONDITIONS.
DANA: A SCHEDULED LIFT-OFF CAN SUDDENLY COME TO A
DEAD STOP. IT CAN MAKE OR BREAK YOUR HOLIDAY WEEKEND. IT CHANGES ALL THE TIME BECAUSE IT’S THE WEATHER!
THE SPACE SHUTTLE LIFTS OFF FROM FLORIDA, WHERE THE
WEATHER IS FAIRLY PREDICTABLE — EXCEPT IN HURRICANE
SEASON. HERE IN THE TEMPERATE ZONE, METEOROLOGISTS
ARE ABOUT 80% ACCURATE IN PREDICTING TOMORROW’S
WEATHER. BUT AFTER THAT, ANYTHING CAN HAPPEN. THIS
IS THE WORLD’S MOST VARIABLE CLIMATE. BUT EVEN PEOPLE
WHO COMPLAIN ABOUT THE WEATHER HAVE TO ADMIT...IT’S
NEVER BORING; IT’S SIMPLY SCIENCE! WHY IS OUR WEATHER
SO UNPREDICTABLE? LOCAL WEATHER RESULTS FROM GLOBAL PROCESSES, AND IT ALL STARTS WITH THE SUN.
STEPHANIE: I’LL HOLD THE SUN.
DARREN: BECAUSE OF THE SHAPE OF OUR PLANET, AND THE
WAY IT TILTS ON ITS AXIS, THE SUN HEATS EARTH UNEVENLY.
STEPHANIE: DIRECT RAYS HIT THE EQUATOR.
DARREN: BUT TOWARDS THE POLAR REGIONS, THE RAYS HIT
AT AN ANGLE.
STEPHANIE: SO THE ENERGY SPREADS OVER A BIGGER AREA?
DARREN: UM-HMM. THESE DIRECT, CONCENTRATED RAYS
MAKE IT MUCH HOTTER HERE AT THE EQUATOR.
STEPHANIE: AND COOLER AT THE POLES.
DARREN: RIGHT. WARM AIR AT THE EQUATOR RISES, CREATING AN AREA OF LOW PRESSURE. AS IT RISES, THIS WARM AIR
COOLS. AND THEN —
STEPHANIE: COOL AIR SINKS. SO FARTHER NORTH, THAT COOL
AIR MUST COME BACK DOWN.
DARREN: YES. AND WHERE IT COMES DOWN, IT MAKES AN
AREA OF HIGH PRESSURE. THESE ARE DESERT REGIONS. THIS
CONSTANT MOVEMENT OF AIR BETWEEN LOW AND HIGH
PRESSURE REGIONS CAUSES GLOBAL CONVECTION CELLS.
SCOTT: WE CAN DEMONSTRATE A CONVECTION CURRENT BY
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USING THIS CONVECTION APPARATUS. I’VE LIT THE CANDLE
UNDER THIS CHIMNEY. THE HEATED AIR FROM THE CANDLE
RISES, THE SAME AS WARM AIR RISES FROM THE SURFACE OF
THE EARTH. COLD AIR RUSHES IN TO TAKE ITS PLACE. THIS
COLD AIR IS HEATED, AND IT RISES, ALLOWING MORE COLD
AIR TO TAKE ITS PLACE. EVENTUALLY, WE SET UP A CIRCULAR
CURRENT. AND IF WE ADD SMOKE — YOU CAN ACTUALLY SEE
THE CURRENT. THE SMOKE IS BEING CARRIED ALONG IN A
CONVECTION CURRENT. IF YOU THINK OF THE CANDLE AS THE
SUN AT THE EQUATOR, WARM AIR RISES, THEN COOLS AND
SINKS BACK DOWN TO EARTH IN THE DESERT REGIONS. WHILE
AT THE EQUATOR, MORE AIR IS WARMED AND RISES.
DARREN: BACK TO EARTH. CONVECTION CURRENTS ARE
PRETTY STRAIGHTFORWARD. BUT BECAUSE WE’RE DEALING
WITH PLANET EARTH, WE HAVE TO ADD A SPIN TO IT.
STEPHANIE: EARTH’S ROTATION. THAT MUST CHANGE THE
CONVECTION CURRENTS.
DARREN: IT DOES. WE CAN USE THIS GLOBE TO SHOW HOW
THE ROTATION BENDS OR DEFLECTS THE CURRENTS. TRY
DRAWING A STRAIGHT LINE FROM THE NORTH POLE TO THE
EQUATOR.
STEPHANIE: THEY ALL CURVE THE SAME WAY.
DARREN: THIS IS KNOWN AS THE CORIOLIS EFFECT. IT DRIVES
THE THREE DOMINANT WINDS ON OUR PLANET: THE TRADE
WINDS, THE WESTERLIES, AND THE POLAR EASTERLIES.
STEPHANIE: AND HERE AT THE EQUATOR THERE AREN’T ANY
WINDS?
DARREN: NO. ALONG THE EQUATOR THERE ARE NO PREVAILING WINDS. THIS IS WHERE WE FIND THE DOLDRUMS. DO YOU
KNOW WHICH WINDS DRIVE OUR WEATHER?
STEPHANIE: MOST OF OUR WEATHER SYSTEMS COME FROM
THE WEST. SO THEY MUST BE DRIVEN BY THE WINDS FROM
THE WEST.
DARREN: RIGHT. THE “WESTERLIES.” NOW, WHAT WE’VE
LOOKED AT SO FAR IS ONLY PART OF THE GLOBAL WEATHER
PICTURE. THERE ARE OTHER WINDS. JET STREAMS IN THE UPPER ATMOSPHERE ZIGZAG AROUND THE GLOBE AT EXTREMELY
HIGH SPEEDS. THEY TRANSFER HEAT FROM THE TROPICS TO
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THE POLES.
STEPHANIE: AND COLD AIR FROM THE POLES TO THE TROPICS?
DARREN: EXACTLY. AND THAT’S A HUGE SYSTEM FOR TRANSFERRING HOT AND COLD AIR AROUND THE GLOBE.
DANA: THERE’S ANOTHER INCREDIBLY LARGE SYSTEM THAT
TRANSFERS HEAT AROUND THE GLOBE — OCEAN CURRENTS.
YOU REMEMBER THAT WATER HAS A VERY HIGH SPECIFIC HEAT
CAPACITY. OCEANS ACT AS GIANT ENERGY STOREHOUSES,
HOLDING THE SUN’S THERMAL ENERGY. WHEN OCEANS ARE
HEATED, CONVECTION CURRENTS FORM IN THE WATER. IT’S
THE SAME PRINCIPLE THAT SETS UP CONVECTION CURRENTS
IN THE AIR. BUT THE MAJOR OCEAN CURRENTS ARE SURFACE
CURRENTS, DRIVEN BY PREVAILING WINDS, MOVING HEAT
ENERGY AROUND THE PLANET.
DARREN: BECAUSE OF EARTH’S ROTATION, AND THE CORIOLIS EFFECT, WATER SHOULD SWIRL ONE WAY DOWN THE DRAIN
IN THE NORTHERN HEMISPHERE AND THE OPPOSITE WAY IN
THE SOUTHERN HEMISPHERE. WHICH WAY DO YOU THINK IT
WILL SWIRL DOWN THIS DRAIN?
STEPHANIE: CLOCKWISE. THE SAME WAY AS THE LINES I DREW
ON THE GLOBE. AND IT DOES!
DARREN: IT DID THIS TIME! IT ISN’T GUARANTEED, BECAUSE
THE SHAPE OF YOUR SINK AND DEBRIS INSIDE THE DRAINPIPE
CAN ALSO INFLUENCE YOUR SWIRL. IN THE OCEAN, NOTHING CAN INTERFERE WITH THE CORIOLIS EFFECT. OCEAN
CURRENTS ALWAYS SWIRL CLOCKWISE IN THE NORTHERN
HEMISPHERE.
STEPHANIE: SO THEY MUST SWIRL THE OTHER WAY, COUNTERCLOCKWISE, IN THE SOUTHERN HEMISPHERE.
DARREN: RIGHT. THE GULF STREAM TRANSFERS HEAT FROM
THE GULF OF MEXICO PAST THE EAST COAST OF NORTH
AMERICA, AND THEN OVER TO
EUROPE.
STEPHANIE: THAT’S WHY BRITAIN IS SO MUCH WARMER THAN
LABRADOR.
DARREN: EVEN THOUGH THEY’RE ALMOST ON THE SAME
LATITUDE.
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STEPHANIE: WHAT ABOUT ON THE PRAIRIES?
DARREN: PRAIRIE CLIMATE IS AFFECTED BY A WARM PACIFIC
CURRENT THAT TRANSFERS HEAT TO THE WEST COAST. IT
STARTS AS THE KUROSHIO CURRENT, NEAR JAPAN. THIS WARM
STREAM TURNS INTO THE NORTH PACIFIC CURRENT AND BECOMES THE ALASKA CURRENT. THE ALASKA CURRENT PRODUCES THE NORTHERN LOW PRESSURE SYSTEMS THAT DETERMINE MOST OF OUR WEATHER PATTERNS.
STEPHANIE: AND THOSE SYSTEMS ARE CARRIED TO US BY THE
WESTERLIES.
DARREN: RIGHT. THEY MOVE IN FROM THE WEST.
DANA: MOST WEATHER SYSTEMS ARE BROUGHT TO US BY
WIND AND WATER. BUT LAND FEATURES CAN ALSO AFFECT
THE WEATHER. MOUNTAINS DISRUPT THE FLOW OF AIR
MASSES AND CHANGE WEATHER
PATTERNS. DESERTS AND FORESTS AFFECT WEATHER PATTERNS. OCEANS, LARGE RIVERS AND LAKES ALSO INFLUENCE
THE WEATHER.
DARREN: AND THAT’S A BRIEF LOOK AT EARTH’S GLOBAL CLIMATE.
STEPHANIE: START WITH THE SUN, AND THE SHAPE AND THE
TILT OF THE EARTH.
DARREN: ADD THE EARTH’S ROTATION, AND YOU HAVE THE
CORIOLIS EFFECT.
STEPHANIE: WHICH RESULTS IN PREVAILING WINDS.
DARREN: JET STREAMS TRANSFER AIR MASSES FROM THE
TROPICS TO THE POLES AND BACK AGAIN.
STEPHANIE: OCEAN CURRENTS STORE THERMAL ENERGY AND
MOVE IT AROUND THE GLOBE.
DARREN: ADD LAND FORMATIONS AND LARGE BODIES OF
WATER, AND YOU HAVE THE MAJOR FACTORS THAT AFFECT
EARTH’S WEATHER. ALL THESE INFLUENCES MAKE WEATHER
FORECASTING A REAL CHALLENGE.
IVOR HUSTON: WELL, WEATHER IS PROBABLY ONE OF THE
MOST IMPORTANT THINGS THAT A PILOT WILL BE CONCERNED
WITH. IT’S SIMILAR TO A SWIMMER, AND HOW IMPORTANT
WATER IS TO A SWIMMER, BECAUSE THEY’RE BOTH IN VIRTUALLY THE SAME TYPE OF SURROUNDINGS — A VERY FLUID
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SURROUNDING. A PILOT, THE FIRST THING HE WOULD BE INTERESTED IN KNOWING IS WHAT THE WIND’S SPEED IS. IT
WOULD BE SIMILAR TO A SWIMMER WANTING TO KNOW IF
HE’S GOING TO BE SWIMMING UPSTREAM OR DOWNSTREAM.
A PILOT WILL WANT TO LAND INTO THE WIND, SO HIS GROUND
SPEED WOULD BE LESS. SO WHEN HE TOUCHES DOWN, HE IS
ACTUALLY GOING SLOWER THAN IF HE WERE GOING WITH
THE WIND, WHICH WOULD MAKE HIM BE GOING FASTER.
THAT’S A LOT HARDER ON BRAKING, CONTROL, AND A NUMBER OF OTHER THINGS AS WELL. ANOTHER VERY IMPORTANT
ISSUE TO PILOTS IS THE VISIBILITY; THAT IS, WHAT YOU CAN
SEE HORIZONTALLY, ALONG THE GROUND. AND OF COURSE,
HOW HIGH UP OR HOW LOW DOWN ARE THE CLOUDS.
RENELLE: WE’RE GOING TO DEMONSTRATE HOW THE SUN’S
RAYS GENERATE MORE HEAT AT THE EQUATOR THAN TOWARD
THE POLES.
ANDY: HERE’S THE EQUATOR. A TIN CAN, PAINTED BLACK SO
THE SUN WON’T REFLECT OFF IT.
RENELLE: IT’S SET ON TOP OF A THERMOMETER, WHICH RESTS
ON EARTH.
ANDY: EARTH IS THIS SHEET OF FOAM-CORE.
RENELLE: THE EQUATOR IS DIRECTLY UNDER THE SUN.
ANDY: HERE WE HAVE A DIFFERENT CLIMATE REGION.
RENELLE: IT LOOKS A LOT LIKE THE EQUATOR, BUT IT ISN’T
DIRECTLY UNDER THE SUN.
ANDY: THIS PIECE OF LAND IS EVEN FARTHER AWAY FROM THE
SUN.
RENELLE: BEFORE THE SUN STARTS SHINING, WE’LL CHECK
THE TEMPERATURES.
ANDY: ALL THE SAME AT 20 DEGREES CELSIUS.
RENELLE: OKAY. TURN ON THE SUN.
ANDY: NOW THE TEMPERATURE AT THE EQUATOR IS —
RENELLE: 59 DEGREES CELSIUS. IN THE TEMPERATE ZONE IT’S
25 DEGREES CELSIUS, AND ONLY 22 DEGREES CELSIUS IN THE
SUBARCTIC ZONE.
ANDY: AT THE EQUATOR, THE TEMPERATURE IS 71 DEGREES
CELSIUS, 28 DEGREES CELSIUS IN THE TEMPERATE ZONE, AND
23 DEGREES CELSIUS IN THE SUBARCTIC.
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RENELLE: SO WHAT DOES ALL THIS DATA TELL US? WELL, DIRECT RAYS FROM THE SUN MAKE AN AREA WARMER.
ANDY: THAT’S BECAUSE THE ENERGY IS CONCENTRATED IN
ONE AREA.
RENELLE: WHEN THE RAYS ARE SPREAD OUT, THE ENERGY IS
SPREAD OUT OVER A LARGER AREA.
ANDY: MEANING THAT LAND CLOSER TO THE POLES GETS LESS
CONCENTRATED RADIANT ENERGY.
RENELLE: AND IT’S HOTTEST AT THE EQUATOR!
DARREN: TALK ABOUT PRESSURE! THIS PLANET COPES WITH
IT 24 HOURS A DAY! PRESSURE IS ONE OF THE MAJOR FACTORS
THAT AFFECTS CLIMATE. AREAS UNDER LOW-PRESSURE CENTERS HAVE LOTS OF CLOUD AND RAIN; FOR EXAMPLE, THE
TROPICAL RAIN FOREST. HOT AIR RISES FROM THE EQUATOR,
LEAVING AN AREA OF LOW PRESSURE. THE WEATHER IS USUALLY CLOUDY AND WET. AREAS DOMINATED BY HIGH-PRESSURE SYSTEMS ARE USUALLY SUNNY AND DRY; FOR EXAMPLE,
THE DESERT. IN THE TEMPERATE ZONE, HIGH-PRESSURE SYSTEMS AND LOW-PRESSURE SYSTEMS ARE CONSTANTLY BUMPING INTO ONE ANOTHER. THE PLACE WHERE THEY MEET IS
CALLED A “FRONT.” THIS IS A MILITARY TERM FOR A PLACE
WHERE BATTLES ARE FOUGHT. IN WEATHER, THE FRONT IS
WHERE TWO AIR MASSES CLASH, CAUSING UNSTABLE CONDITIONS. AROUND HERE, WARM AND COLD AIR MASSES CLASH
ALL THE TIME, GIVING US THE MOST VARIABLE WEATHER ON
THE PLANET. OH, IS THAT RAIN?
SHELLEY HUMPHRIES: IF YOU LIVE NEAR THE MOUNTAINS,
YOU’RE AFFECTED BY PRESSURE. TAKE THE ROCKIES, FOR EXAMPLE. PREVAILING WINDS COMING FROM THE WEST BUMP
INTO THE MOUNTAINS. THE AIR RISES TO GO OVER. AND AS IT
RISES, IT COOLS, CLOUDS FORM, AND THEN RAIN OR SNOW
FALLS. AS THE WATER VAPOR CHANGES INTO LIQUID OR ICE,
THERMAL ENERGY IS RELEASED INTO THE AIR, MAKING IT
WARMER. WARM, DRY AIR DESCENDS ON THE EAST SIDE OF
THE MOUNTAINS. THIS AIR HAS HIGHER PRESSURE AND
PUSHES AWAY OTHER AIR MASSES. THE CLIMATE ON THE WEST
SIDE OF THE MOUNTAINS IS WET, AND ON THE EASTERN SIDE
IT IS DRY. THIS IS CALLED THE RAIN SHADOW EFFECT. THE
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EASTERN SIDE IS IN THE RAIN SHADOW OF THE MOUNTAINS.
SOMETIMES, AS THE WIND DESCENDS THE EASTERN SLOPES
IT CREATES A CHINOOK. DURING A CHINOOK, THE TEMPERATURE CAN RISE BY MORE THAN 20 DEGREES CELSIUS IN ONE
HOUR.
DARREN: HOW DO FORECASTERS KNOW IF IT’S GOING TO BE
SUNNY OR CLOUDY TOMORROW? AND IF THEY KNOW, WHY
AREN’T THEY ALWAYS RIGHT? AT A FORECASTING CENTER,
METEOROLOGISTS STUDY WEATHER PATTERNS 24 HOURS A
DAY.
CLAIRE MARTIN: NOW, THERE ARE TWO SYSTEMS WE REALLY
SHOULD BE LOOKING AT. ONE, IN THE NORTHEAST
CORNER...ACTUALLY, SPIRALING JUST OUTSIDE OF
YELLOWKNIFE THERE, AND IT’S SWINGING IN...
BRYCE: SO CLAIRE, HOW DO YOU COME UP WITH A REALLY
ACCURATE WEATHER FORECAST?
CLAIRE MARTIN: IT’S REALLY EASY. YOU LOOK OUT THE WINDOW. THERE’S NOT A CLOUD IN THE SKY. IT’S NOT GOING TO
RAIN FOR THE NEXT 30 MINUTES. OF COURSE, WHEN YOU
CAN’T SEE BEYOND THE HORIZON, THAT’S WHEN YOU START
TO GET INTO DIFFICULTIES. BUT THERE ARE, ACTUALLY, CERTAIN THINGS THAT WE CAN DO THAT WILL HELP TO MAKE A
BETTER FORECAST. TWO OF THEM ARE VERY IMPORTANT. THE
FIRST ONE IS OBSERVATIONS. AT EVERY HOUR, ON THE HOUR,
AROUND THE WORLD, THOUSANDS UPON THOUSANDS OF
PEOPLE GO OUT AND TAKE AN OBSERVATION OF THE
WEATHER. THEY LOOK AT TEMPERATURE, WIND, HUMIDITY,
PRESSURE. ALL THIS INFORMATION IS THEN PULLED INTO
NUMERICAL MODELS, AND THESE MODELS ARE LIKE CEMENT.
SAY THE OBSERVATIONS ARE BRICKS OF A BUILDING HOUSE;
THE MODELS ARE THE CEMENT. AND FROM THAT, WE CAN
GENERATE A FAIRLY GOOD FORECAST.
BRYCE: IS THERE A SPECIFIC TIME OF YEAR AT WHICH IT’S
EASIER TO FORECAST THAN OTHERS?
CLAIRE MARTIN: WE CAN ACTUALLY SPLIT, SORT OF, SEASONAL AND TIME INTO ABOUT FOUR MAIN AREAS. THE FIRST
AREA IS SHORT-RANGE FORECASTING, SAY, UP TO ABOUT 12
HOURS. AND WE HAVE GREAT SKILL FORECASTING UP TO 12
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HOURS — UNLESS WE’RE TALKING ABOUT SMALL SCALE
EVENTS, LIKE A TORNADO, WHICH IS REALLY ONLY FORECASTABLE ABOUT A FEW MINUTES PRIOR TO THE EVENT OCCURRING. THE NEXT AREA IS FROM 12 TO 48 HOURS. AGAIN,
WE HAVE CONSIDERABLE SKILL, ESPECIALLY WITH LARGE PACIFIC STORMS, SAY, COMING IN FROM THE WEST. WE CAN TIME
THOSE QUITE NICELY. THEN WE GET INTO SORT OF THE
LONGER RANGE, SAY, THREE TO FIVE DAYS AND THE SKILL
TAILS OFF SOMEWHAT. WE CAN STILL DO TEMPERATURE
TRENDS QUITE WELL. THE MONTHLY SEASONAL FORECAST
— THAT’S REALLY JUST A GENERIC OUTLOOK, AND THERE IS
VERY SMALL SKILL THERE. NOW, ALL OF THAT COMES UNDER
ONE MAJOR HEADING, THOUGH. ABOUT 40 YEARS AGO, A GUY,
EDWARD LORENZ, CAME OUT WITH THE CHAOS THEORY,
WHICH HAS TURNED THE WEATHER WORLD ON ITS HEAD
BECAUSE IT BASICALLY GAVE US AN ULTIMATE LIMIT AS TO
HOW FAR WE CAN FORECAST. AND AT THE MOMENT IT LOOKS
LIKE , WITH THE PHYSICS BACKGROUND THAT WE HAVE RIGHT
NOW, WE CAN’T FORECAST MORE THAN ABOUT TWO WEEKS
PRIOR TO THE EVENT.
BRYCE: SO WHAT DO THE LINES ON THIS MAP MEAN?
CLAIRE MARTIN: IT’S A SURFACE ANALYSIS FOR CANADA. YOU
CAN SEE ALL OF CANADA HERE, AND I’VE HIGHLIGHTED IN
ALBERTA JUST THERE. THERE’S TWO THINGS THAT ARE REALLY
INTERESTING ON THIS WEATHER MAP. EVERY FORECASTER IN
THE WORLD USES ONE OF THESE. THE SQUIGGLY LINES THAT
YOU CAN SEE RUNNING AROUND THE COUNTRY ARE ACTUALLY EQUAL-PRESSURE LINES. MUCH LIKE YOU GET A TOPOGRAPHICAL MAP SHOWING HEIGHT LINES, THIS IS VERY SIMILAR. AS YOU GO IN TOWARDS THE “L’S” HERE, THIS IS ACTUALLY AN AREA OF LOW PRESSURE. SO EACH OF THESE LINES
COMES DOWN IN PRESSURE BY AN EQUAL, OR A SAME SEGMENT. SAME FOR THE HIGH PRESSURE. THE PRESSURE IS RISING AS YOU GO UP TOWARDS THE NORTHEAST OVER THERE.
NOW, THE SECOND SET OF LINES THAT YOU CAN SEE ON HERE
ARE FRONTS, THESE GUYS HERE. THEY WERE ACTUALLY
NAMED DURING THE FIRST WORLD WAR BY A GUY NAMED
BJERKNES WHEN THEY WERE THINKING ABOUT ARMIES
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CLASHING. THESE FRONTS SHOW THE MARKED CHANGE BETWEEN A WARM AIR MASS AND A COLD AIR MASS. THE AIR IS
COLDER HERE THAN IT IS AHEAD OF IT. THE SPIKES SHOW A
COLD FRONT, AND THE BUBBLES UP HERE SHOW A WARM
FRONT.
BRYCE: SO WHAT DO SATELLITE IMAGES TELL US?
CLAIRE MARTIN: WELL, LET’S TAKE A LOOK OVER HERE AND
I’LL SHOW YOU.\E OKAY. SO THIS IS WHERE WE GET TO SEE
OUR SATELLITE IMAGERY FROM. THE FIRST THING YOU’RE
GOING TO NOTICE IS A LOT OF GREY. THIS IS ACTUALLY LIKE A
PHOTOGRAPH. IT SHOWS THE CLOUD COMING IN FROM THE
WEST. HERE’S THE PROVINCE OF ALBERTA OUTLINED IN WHITE.
SO THE SATELLITE IMAGERY ALLOWS US TO SEE WHERE WE
CAN’T SEE ON THE HORIZON. SO THE SKY MIGHT BE CLEAR
RIGHT NOW, BUT THE STUFF IS BUILDING WEST OF US OUT IN
JASPER AND EDSON. AND THAT’S GOING TO COME OUR WAY.
THE BEAUTY OF SATELLITE IMAGERY IS IT SHOWS US THUNDERSTORMS DEVELOPING WELL OUT OF OUR AREA THAT WILL
COME INTO OUR AREA SOON. SO IT’S A GREAT FORECASTING
TOOL WHEN IT COMES TO THUNDERSTORMS.
DANA: THUNDERSTORMS ARE ONE WAY FOR EARTH TO REDISTRIBUTE THERMAL ENERGY. ON A HOT DAY, WARM AIR
NEAR THE GROUND RISES, CREATING AN UPDRAFT. AS THE
WARM AIR FLOWS UPWARDS, IT COOLS, CONDENSES, AND
FORMS CLOUDS. AS WATER VAPOR BEGINS TO CONDENSE, IT
RELEASES ENERGY, FUELING A CONTINUOUS UPDRAFT. UNDER CERTAIN CONDITIONS, THUNDERCLOUDS CAN REACH
RIGHT UP TO THE STRATOSPHERE. WATER AND DUST MOLECULES COLLIDE SO FREQUENTLY THAT THEY LOSE ELECTRONS. WATER DROPLETS IN THE LOWER SECTION OF THE
CLOUD BECOME NEGATIVELY CHARGED. HIGH UP IN THE
CLOUD, ICE CRYSTALS BECOME POSITIVELY CHARGED. THIS
SETS UP CONDITIONS FOR A VERY LARGE ELECTRICAL SPARK,
CALLED LIGHTNING. THE STRONG UPDRAFT KEEPS PRECIPITATION FROM FALLING UNTIL FINALLY THE WEIGHT OF THE
WATER DROPLETS BRINGS THEM DOWN TO EARTH. THIS
CAUSES A DOWNDRAFT, AND THE STORM BEGINS. EACH UPDRAFT/DOWNDRAFT COMBINATION IS CALLED A STORM
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CELL.
STEPHANIE: THIS LAVA LAMP ACTS A BIT LIKE A STORM CLOUD.
A LIGHT BULB IN THE BOTTOM HEATS THE COLORED BLOB OF
WAX. WHEN THIS GETS HOT, IT RISES, JUST LIKE HOT AIR RISING IN THE ATMOSPHERE. AT THE TOP, IT COOLS JUST ENOUGH
TO BECOME DENSER THAN THE OIL, AND
SINKS BACK DOWN TO THE BOTTOM WHERE IT’S HEATED
AGAIN. THE LAVA LAMP IS ANOTHER EXAMPLE OF A CONVECTION CURRENT.
DARREN: THUNDERSTORMS ARE ONE WAY THIS PLANET KEEPS
FROM OVERHEATING. THEY OCCUR AT A RATE OF ABOUT 40,000
EVERY DAY.
RENELLE: AMAZING WE DON’T HAVE ONE HERE RIGHT NOW!
DARREN: THEY’RE GOOD FOR THE PLANET. BUT SEVERE THUNDERSTORMS CAN CAUSE BIG PROBLEMS.
RENELLE: LIKE HIGH WINDS.
DARREN: HEAVY RAINS.
RENELLE: SOMETIMES HAIL.
DARREN: EVEN TORNADOES! AND OVER WARM OCEAN WATERS, THEY CAN CREATE HURRICANES.
RENELLE: THAT’S WHY WE RELY SO MUCH ON WEATHER FORECASTS!
BRYCE: SO WHAT’S THE BUSIEST TIME OF THE YEAR HERE AT
THE WEATHER STATION?
CLAIRE MARTIN: WE’RE ACTUALLY IN THE NORTHERN
ALBERTA ENVIRONMENTAL SERVICES CENTER, AND THEY REALLY KICK INTO HIGH GEAR ONCE WE GET INTO SEVERE
WEATHER SEASON. ABOUT FROM THE MIDDLE OF MAY TO THE
MIDDLE OF OCTOBER WE START TO SEE A LOT OF THUNDERSTORMS HERE, BECAUSE WE’VE GOT ALL THAT EXTRA ENERGY
FROM THE SUN. AND THAT’S WHEN THEY REALLY START TO
NEED THE FORECASTERS. NOW, THERE’S ANOTHER TOOL THAT
WE TEND TO USE HERE. YOU’VE SEEN THE SATELLITE IMAGERY. AS I’VE SAID, THAT’S KIND OF LIKE A PHOTOGRAPH. WELL,
THEY ALSO TEND TO USE RADAR, AS SHOWN ON THE SCREENS
UP HERE. NOW, WHEREAS SATELLITE IMAGERY IS A PHOTOGRAPH, RADAR IS KIND OF LIKE AN X-RAY. IT TELLS US WHAT’S
HAPPENING INSIDE THE CLOUD.
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ANDY: WHEN YOU WORK ON THE OPEN SEA, ACCURATE
WEATHER INFORMATION CAN BE A LIFE AND DEATH MATTER.
WEATHER REPORTS ARE IMPORTANT FOR EVERYONE...PEOPLE
WHO WORK OUTSIDE, AND EVERYONE WHO DRIVES OR WALKS
TO WORK OR SCHOOL. ANYONE WHO’S PLANNING AN OUTDOOR EVENT KNOWS WHAT A ROLE THE WEATHER CAN PLAY.
FARMERS REALLY DEPEND ON GOOD WEATHER CONDITIONS.
CROPS NEED CERTAIN TEMPERATURES, AND THE RIGHT
AMOUNT OF RAIN AND SUNSHINE. SEVERE STORMS CAN DAMAGE THE CROP, AND A HAILSTORM CAN MEAN DISASTER!
CLAIRE MARTIN: HAIL IS FORMED, ACTUALLY, BY THUNDERCLOUDS. THE FIRST THING YOU HAVE TO HAVE IS A THUNDERSTORM GOING ON. YOU THEN FIND SUPER-COOLED DROPLETS
OF WATER IN THAT CLOUD GETTING LIFTED UP BY THE UPDRAFT. SO THEY’RE TAKEN HIGHER UP INTO THE CLOUD
WHERE IT’S COLDER. SO THEY FREEZE. AS THEY FREEZE THEY
GET HEAVIER. THEY FALL. NOW, AS THEY FALL, THEY FALL INTO
A WARMER PART OF THE CLOUD, AND YET MORE SUPERCOOLED WATER GOES ONTO THEM, AND ARE THEN LIFTED UP.
SO THAT TOSSING OF GOING UP AND DOWN IN THE CLOUD
GOES ON FOR QUITE A WHILE. EVENTUALLY, THE CLOUD
CAN’T HOLD THEM UP ANYMORE. THEY’RE TOO HEAVY, AND
THEY COME SLAMMING DOWN TO EARTH, GENERALLY HITTING PEOPLE’S CARS. YOUR VERY SEVERE THUNDERSTORM
WILL PRODUCE A TORNADO. AND THESE ARE EVEN MORE
DAMAGING, OBVIOUSLY, THAN HAIL IS. AND IN FACT, A TORNADO IS STILL BASICALLY ONE OF THE SMALL WEATHER EFFECTS THAT, AS FAR AS FORECASTING GOES, STILL ELUDES US.
WE STILL FIND IT VERY HARD TO ISSUE A TORNADO WARNING
MORE THAN 15 MINUTES, AT BEST, IN ADVANCE.
DANA: ON JULY 31, 1987, A TORNADO STRUCK THE CITY OF
EDMONTON, ALBERTA. IT TRAVELED ALONG THE GROUND
FOR OVER AN HOUR, WITH WINDS OF MORE THAN 300 KILOMETERS PER HOUR. THE TORNADO KILLED 27 PEOPLE, AND
CAUSED MORE THAN 250 MILLION DOLLARS IN DAMAGE.
WHEN A TORNADO FORMS, THE STORM CELL’S UPDRAFTS AND
DOWNDRAFTS COMBINE TO PRODUCE A ROTATING COLUMN
WITHIN THE CLOUD. THIS CAN TIGHTEN AND PUSH DOWN
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TOWARDS THE GROUND IN A FUNNEL SHAPE. WHEN THE FUNNEL REACHES THE GROUND IT’S CALLED A TORNADO. TORNADOES PRODUCE THE STRONGEST WINDS ON EARTH,
REACHING UP TO 500 KILOMETERS PER HOUR.
DARREN: FORTUNATELY, ONLY 1% OF THUNDERSTORMS EVER
TURNS INTO A TORNADO.
RENELLE: AND THAT’S A GOOD THING!
ANDY: HERE ON THE PRAIRIES, OUR WEATHER IS AFFECTED
BY LATITUDE AND THE EARTH’S TILT.
STEPHANIE: AS WELL AS GEOGRAPHIC FEATURES AND PREVAILING WINDS.
ANDY: THE SUN’S RAYS ARE DIFFUSED AS THEY HIT US, WHICH
CAN MAKE WINTER VERY COLD.
STEPHANIE: THESE LINES ARE ISOBARS. THEY RUN ALONG THE
AREAS THAT HAVE THE SAME ATMOSPHERIC PRESSURE.
ANDY: A HIGH-PRESSURE SYSTEM CAN USUALLY MEAN FAIR
WEATHER.
STEPHANIE: AND A LOW-PRESSURE SYSTEM BRINGS UNSTABLE
CONDITIONS AND PRECIPITATION.
ANDY: THERE AREN’T ANY LARGE BODIES OF WATER OR
OCEANS AROUND TO MODERATE THE CLIMATE.
STEPHANIE: BY COMPARISON, TEMPERATURES ALONG THE
WEST COAST ARE WARMER IN THE WINTER AND COOLER IN
THE SUMMER.
ANDY: THAT’S BECAUSE THEY’RE MODERATED BY THE PACIFIC
OCEAN.
STEPHANIE: OUR WEATHER SYSTEMS USUALLY COME FROM
THE WEST, BECAUSE THE PREVAILING WINDS ARE THE WESTERLIES.
ANDY: AND TODAY, WE CAN EXPECT A WARM AIR MASS...FROM
THAT DIRECTION.
STEPHANIE: IT WILL MEET WITH THE COLD AIR MASS THAT IS
OVER THE PROVINCE RIGHT NOW.
ANDY: THE PLACE WHERE THEY MEET IS CALLED THE FRONT.
WE’LL HAVE UNSETTLED WEATHER ALONG THE FRONT.
STEPHANIE: THAT MEANS STRONG WINDS AND PRECIPITATION THE “POP,” OR PROBABILITY OF PRECIPITATION, IS 80%.
ANDY: HOW LONG WILL THIS UNSETTLED WEATHER STAY
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OVER THIS AREA?
STEPHANIE: WEATHER FORECASTERS ARE USUALLY PRETTY
GOOD AT PREDICTING THE NEXT 24 HOURS.
ANDY: BUT AFTER THAT, THE PREDICTIONS AREN’T SO ACCURATE.
STEPHANIE: IF YOU WANT TO KNOW THE LONG-RANGE
WEATHER FORECAST, THE BEST ADVICE IS “WAIT AND SEE.”
ANDY: AND THAT’S TODAY’S WEATHER!
DANA: THE ENERGY THAT DRIVES THE WEATHER COMES
FROM THE SUN. WIND AND WATER DISTRIBUTE THAT ENERGY
AROUND THE WORLD. IT’S SIMPLY SCIENCE!
26
1
Name___________________________________
PRE-TEST
Directions: Circle the letter indicating whether the following statements are either true ("T") or false
("F").
T
F
1.
Warm air rises due to an increase in density.
T
F
2.
A volume of gas cools when allowed to expand rapidly.
T
F
3.
A warm air mass can hold less moisture than a cooler one at the same pressure.
T
F
4.
Convection currents in fluids are the result of unequal heating.
T
F
5.
Large bodies of water have little effect on the climate in adjacent land areas.
T
F
6.
Water can absorb and release large amounts of thermal energy.
T
F
7.
Winds are the result of unevenly heated air masses.
T
F
8.
The amount of precipitation in a region is not affected by transpiration from
plants.
T
F
9.
Evaporation from large bodies of water has a significant impact on the weather
of the region.
T
F
10.
The terms climate and weather are synonymous.
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GLOSSARY
Air mass – a large volume of the lower atmosphere with uniform temperature and humidity
Barometric pressure – the air pressure measured in kilopascals
Climate graph – a graph showing simultaneously the average daily minimum, maximum and average
monthly temperatures, as well as the average monthly precipitation for a particular place
Convection – a transfer of thermal energy by medium molecules moving from one place to another
Convection current – the flow of a fluid, such as air, due to uneven heating; warm air rises and cool air
moves in to takes its place
Coriolis effect – the deflection of wind and water currents on Earth due to the spinning of the planet
Front – the boundary between two air masses; usually the site of unsettled weather
Isobar – a line on a weather map which connects areas of equal air pressure; winds tend to blow along
isobars
Weather – the condition of the atmosphere with respect to temperature, humidity, wind and clouds for
a period of time
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THE GLOBAL PICTURE: AIR CURRENTS
List some factors which you think affect the weather.
Weather is affected by distance from the equator (latitude), distance from large bodies of water, local
geography, prevailing winds and number of daylight hours (or season).
Uneven heating of the surface of Earth results in air movement around the globe. How does heating the
surface cause the air to move? The second law of thermodynamics explains that heat flows from a
hotter object to a cooler one. As Earth warms, thermal energy from the soil is transferred to the cooler
air above it. Heating of the air causes it to expand, making it less dense, so it rises. The swirling motion
of warm air rising and cool air moving in to take up the space is called a convection current.
The atmosphere is also affected by the spin of the planet. As Earth rotates on its axis the atmosphere is
dragged along with it. This causes the air currents to be deflected and is called the Coriolis effect.
Together, convection and the Coriolis effect determine the prevailing wind directions across our globe.
Check your understanding of this segment by completing the following. Use the back of the sheet if
necessary.
1. Explain why convection currents rise at the equator.
2. The polar winds are called polar easterlies. Do they blow from the east, or to the east?
3. Refer to the model below to explain how equal amounts of solar energy cause uneven heating of
the surface of earth.
a quantity
of solar radiation
polar region
temperate region
equatorial region
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THE GLOBAL PICTURE: WATER CURRENTS
Fill a sink with water and then gently remove the plug; note which way the water swirls (clockwise or
counterclockwise). Repeat the procedure a few times, then try a different sink. Why does the water
swirl, instead of simply flowing straight down?
Temperature
Compare the weather of two locations that
are similar except that one is near a large
body of water and the other is not. What
should we expect to find? We know that
water has a very large specific heat capacity,
meaning that it can store a great deal of
thermal energy. We also know that the
amount of water vapor in the air can affect
the weather. Other factors make it difficult to
answer the question firmly; wind patterns
and geography also affect the weather
considerably.
A climate graph shows the average monthly
temperature and the average monthly precipitation for one location. The following is
the climate graph for Calgary, Alberta.
20
15
10
(°C) 5
0
-5
-10
-15
Precipitation
200
190
180
423.8 mm
Annual Average
170
160
150
140
130
120
(mm) 110
100
90
80
70
60
50
40
30
20
10
0
© 1997 Alberta Education
J
F
M
A
M
J
J
(month)
A
S
O
N
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THE GLOBAL PICTURE: WATER CURRENTS
Check your understanding of this segment by completing the following. Use the back of the sheet if
necessary.
4. Explain why the specific heat capacity of water can affect weather and climate.
5. Create a climate graph for Vancouver using the average monthly temperature and precipitation data
given below.
6. Compare and contrast the climate graphs for Vancouver and Calgary.
7.
Identify the major factors that make these two cities’ climates so different.
Note: Calgary is approximately 200 km north of Vancouver.
8. Design an experimental procedure that would show how heating affects dry air compared to humid
air (air which contains water vapour).
Average Temperatures and Precipitation for Vancouver, British Columbia
Month
Average Monthly
Temperature (°C)
Average Monthly
Precipitation (mm)
January
2.5
153.8
February
4.6
114.7
March
5.8
101.0
April
8.8
59.6
May
12.2
51.6
June
15.1
45.2
July
17.3
32.0
August
17.1
41.1
September
14.2
67.1
October
10.0
114.0
November
5.9
150.1
December
3.9
182.4
Annual Total: 1112.6
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PREDICTING THE UNPREDICTABLE
Identify the information commonly provided by weather forecasters.
Weather forecasts generally detail expected precipitation, temperature, wind conditions and, in some locations,
humidity and barometric pressure.
Weather maps provide information about air masses, winds, temperature and areas called “fronts.” A
front is an area in which two different air masses are colliding. Fronts often bring precipitation, but they
can be of two types.
Warm fronts occur when a warm air mass blows over a cooler air mass. As it travels up, the warm air
cools and, as a result, cannot hold as much moisture. Warm fronts are associated with long periods of
overcast skies and precipitation.
A cold front is also the result of warm and cool air masses colliding, but here the cool air mass blows into
the warm air and pushes it upward quickly. The warm air cools rapidly, and severe, but short, storms
often result.
Check your understanding of this segment by completing the following. Use the back of the sheet if
necessary.
9. Based on the weather map above, which cities have a warm front approaching?
10. Explain why the cold fronts on the map all have warm fronts associated with them.
11. Which cities are likely to experience severe, short storms?
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STORMS
Check your understanding of this segment by completing the following. Use the back of the sheet if
necessary.
12.. Thunderstorms occur most often in the afternoon or evening on hot summer days. Why do hot
sunny days lead to thunderstorms?
13.. Draw arrows to show the updrafts and downdrafts that occur, first as a thunderhead develops, and
then as it releases a downpour of rain.
14. Describe the process that can cause the large pieces of ice called hail to form during a storm.
15. Why is the fact that water has a high heat of vaporization important to the development of a thunderstorm?
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PRAIRIE WEATHER
We have already seen how fronts can help us predict the weather. Local air pressure can also be a
valuable tool.
On a weather map a capital “H” indicates an area of high air pressure – these areas usually have clear
skies. What’s the connection? First we have to consider how pressure affects water vapour in the air.
When we increase the pressure of a gas (like the atmosphere) its temperature also increases. Since air at
warmer temperatures can hold more water vapour, water in the air stays as vapour and clouds do not
form.
Try this: take a deep breath and slowly release it – note any observations. Repeat the process, only this
time breath into a freezer – again note any observations.
Low pressure areas often bring clouds and precipitation. Warm moist air expands as the pressure drops.
The expanding air becomes cooler, and water vapour in the air condenses into clouds. Low pressure
systems usually bring precipitation.
Check your understanding of this segment by completing the following. Use the back of the sheet if
necessary.
16. Using weather maps printed in your local newspaper, together with what you have learned about
fronts and pressure systems, predict the cloud cover and precipitation that will occur where you live.
Do it every day for one week. Record your predictions and make observations so that you can compare.
17. Use the weather maps to track the movement of a low pressure system for one week. Use what you
know about prevailing wind patterns to predict its movement across the map.
18. Based on the map above, describe the likely weather in Toronto.
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8a
POST-TEST
MULTIPLE CHOICE
Directions: Decide which of the choices best completes the statement or answers the question,
then circle the letter that corresponds to your choice. (3 marks each)
1.
Violent, but short, storms often accompany
a.
b.
c.
d.
2.
The Coriolis effect is demonstrated by
a.
b.
c.
d.
3.
cold fronts
warm fronts
Earth's rotation
prevailing winds
The climactic region known as the doldrums is located
a.
b.
c
d.
4.
cold fronts
warm fronts
rising pressure
stationary fronts
near the equator
in the mid latitudes
near the north polar region
near the south polar region
The most varied weather occurs in the
a.
b.
c.
d.
subtropical rain forests
temperate zones
polar regions
tropics
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8b
Name___________________________________
POST-TEST
LONG ANSWER
Directions: Answer the following questions in the spaces provided. Use the back of the sheet if necessary.
1.
Earth's Atmosphere and surface is heated unequally due to ___________________________
______________________. (3 marks)
2.
High speed winds, flowing in narrow bands, at high altitudes are known as ______________
_____________________. (3 marks)
3.
Isobars on a weathermap indicate areas of ______________________________. (3marks)
4.
Explain why atmospheric low pressure regions predominate at the equator and high pressure
regions are more prevalent at higher latitudes, 30° N for example. (6 marks)
5.
Thermal energy on Earth is distributed by means of two global systems, they are
__________________ and ________________________. (6 marks)
6.
Describe the conditions which lead to the formation of a thunder cloud. (6 marks)
7.
The meteorological phenomenon called a "storm cell" consists of an ___________________
___________________________________ combination. (3 marks)
8.
How does the electrical charge separation in a cloud, leading up to a lightning strike, occur? (6
marks)
© 1997 Alberta Education
Distributed by AGC/United Learning
AGC/United Learning • 1560 Sherman Ave., Suite 100 • Evanston, IL 60201 • 800-323-9084
8c
Name___________________________________
POST-TEST
9.
Draw the symbol used on weather maps indicating a warm front. (4 marks)
10.
During the winter months, a dry warm wind frequently descends the eastern slopes of the Rocky
Mountains of western Canada and the northwestern United States. Briefly explain why a chinook
consists of a rapidly moving dry and warm air mass. (6 marks)
11.
Draw the symbol used on weather maps indicating a stationary front. (4 marks)
12.
Explain why clear skies are usually associated with high pressure areas. (6 marks)
13.
Describe the process which produces hail stones in a cloud. (6 marks)
14.
List four geographic features which influence local weather. (8 marks)
____________________________________________________
____________________________________________________
____________________________________________________
____________________________________________________
© 1997 Alberta Education
Distributed by AGC/United Learning
AGC/United Learning • 1560 Sherman Ave., Suite 100 • Evanston, IL 60201 • 800-323-9084
8d
Name___________________________________
POST-TEST
15.
Climate graphs show the _________________________ and _________________________ for a
particular location. (6 marks)
16.
17.
Differentiate between climate and weather. (6 marks)
Two weather creating differences between warm and cold air masses are:
_____________________________________________________________________ and
________________________________________________________________. (6 marks)
© 1997 Alberta Education
Distributed by AGC/United Learning
AGC/United Learning • 1560 Sherman Ave., Suite 100 • Evanston, IL 60201 • 800-323-9084