WEATHER FORECAST
Clear skies ahead!
Weather forecasts, whose inaccuracies we are always pleased to
point out, are the result of centuries of observation, very sophisticated
models, countless measurements and thorough calculations. To
complete its flight across the oceans, which will last several days, the
Solar Impulse team will have to push the limits of today’s forecasts.
This worksheet gives students the opportunity to tackle a subject that
touches their everyday life: the weather. After a historical overview,
we will discuss the factors affecting the weather so that students have
the necessary elements to understand forecasts. Also, we propose
the construction of simple prototypes of meteorological measuring
instruments. The development of these devices or the discovery of
other models can be carried out individually or in teams, either in the
context of the OCOM or as a school project. This subject also provides
an opportunity to practice measuring and charting various weather
parameters.
Please note that the CLOUDS worksheet presents the different types
of clouds in more detail, as well as their formation and the phenomena
associated with them (rain, frost, hail, lightning, snowflakes, etc.)
Project: EPFL | dgeo | Solar Impulse
Writing: Marie-Noëlle Kaempf
Graphic design: Anne-Sylvie Borter, Repro – EPFL Print Center
Project follow-up: Yolande Berga
1/15
Concepts covered
Science
• Water cycle
• Meteorology and clouds
• How to measure different parameters
Geography
• Atmospheric circulation
• Weather
Physics
• Energy transformations
• Pressure
Mathematics
• Unit conversion
• Volume calculation
• R
eading and sorting data, reading and creation of charts
Activity duration
Introduction to theoretical concepts: 3 periods
Exercises: 2 periods
Practical work: it will depend on the chosen
project
A PRECEDENT...
Even though nobody in Switzerland could have possibly missed the around-the-world journey of Breitling Orbiter 3 in 1999, today’s students may not yet have been born. Therefore, they should be told
about it, especially given that Bertrand Piccard was at the origin of the project.
Here is a video summing up the adventure:
www.ina.fr/video/CAC99012266
ina, Record tour du monde en ballon
It all ended well. The balloon took off on March 1st, 1999 in Château d’Oex, Switzerland, and landed in
Egypt 19 days later, after completing the longest nonstop flight in aviation history in terms of duration
and distance.
More information can be found on the site:
bertrandpiccard.com/tour-du-monde-en-ballon
bertrandpiccard.com, Tour du monde en ballon
WHAT IS METEOROLOGY?
The following is an outline of the history of meteorology. It will allow you to answer some questions or tell
some anecdotes to complement your lessons.
The first hints of observations and weather forecasts are found on the 1st millennium BC in China, in a
medical book that includes humans and their environment. In 400 BC we find the first monsoon precipitation measurements In India. At this same time, the Greeks were questioning the phenomena around
them. Aristotle described the water cycle and Theophrastus published the first
book on western meteorology: “The weather signs.” The Middle Ages brought
no contribution to the scientific foundations laid in antiquity. Farmers relied on
popular sayings and cloud observations.
The first significant instruments of meteorology were invented during the
Renaissance. In 1644 Torricelli invented the mercury barometer to solve the
problems of Florence’s fountain gardens. Blaise Pascal continued his work
and was convinced that the atmospheric pressure is exerted by the air above
us. This led him to deduce that pressure decreases with altitude. In September 1648 he sent his brother to climb the Puy de Dome equipped with a barometer, thereby proving his theory.
Ferdinand II de’ Medici, the Grand Duke of Tuscany, was more passionate
about sciences than politics. He was Galileo’s and then Torriceli’s diligent
student. With his brother Leopold, he created the first scientific academy in
Europe in his palace in Florence (Palazzo Pitti). In 1654 he perfected a water
model to create a real thermometer. It had 50 graduations. It was filled with
alcohol trapped in a glass tube.
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Research in Italy was widespread, but Britain was not far behind. In 1667, Robert Hooke conducted
research with an anemometer. Halley mapped the trade winds in 1686 (see the text box in the student
worksheet).
Robert Hook (1635 - 1703) was a scientist, who was passionate about
carrying out experiments. He made a number of observations using
a microscope and become the first to provide a detailed description
of cells. He improved his microscope by adding a system of lenses.
To this day we use his name to refer to the law of elasticity that he
discovered.
Hook invented many devices. He is the father of the acoustic telephone, several moving parts used in watches, and also of a telescope.
As measurement instruments spread and measurement units were centralized, observation networks
were created. The invention of the telegraph facilitated communications between different measurement stations. Thus it was possible to verify that cloud formations move around the globe, and that
it was possible to predict the weather. The release of balloons in the early 20th century confirmed the
movement of air masses and the weather changes according to their interactions.
The armies involved in the First World War invested heavily in meteorology research. Indeed, troop
deployments, as well as the deployment of air and maritime fleets, were planned according to weather
forecasts.
It was discovered by chance that the radars used during World War II were recording the echoes of
precipitations. This was initially considered a nuisance, but soon afterwards, radars were introduced to
improve the collection of weather data. But the two tools that revolutionized weather forecasting were
satellites, and since 1960, information technology. Indeed, the data collected by satellites are accurate
and cover large areas, many of which are uninhabited and difficult to reach, such as as the poles, the
deserts and the oceans. Finally, computer processing of weather data and the use of numerical models
yield reliable predictions.
Meteorologist Edward Lorenz stated the following problem at a conference in 1972:
“Predictability: does the flap of a butterfly’s wings in Brazil set off a tornado in Texas? »
This question raised the issue of the now-famous “butterfly effect,” which reflects the difficulty (or
impossibility) of predicting the weather (or any other chaotic system) in the long run without perfect
knowledge its initial conditions or of all the little events whose effects could have a significant impact
over time. Although more recent research has shown that these small effects are fade in importance
in the face of the mass of more significant atmospheric events, it is clear that with today’s knowledge,
weather forecasts are not very reliable more than five days into the future.
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WEATHER FORECAST - GUIDE
Quiz
What does each instrument measure?
Pluviometer
•
• Wind speed
Heliometer
•
• Wind direction
Barometer
•
• Atmospheric pressure
Thermometer •
Anemometer
•
Weather vane •
Hygrometer
•
• Precipitations
• Humidity
• Solar radiation
• Temperature
Here are links to two episodes of the podcast “Si ça n’existait pas… (If it did not exist…)” hosted by
RTBF, on the history and operation of two basic meteorological instruments: the barometer and thermometer.
www.rtbf.be/lapremiere/article_invention-le-barometre?id=6985123
rtbf, invention, Le baromètre
www.rtbf.be/lapremiere/article_invention-le-thermometre?id=6093273
rtbf, invention, Le thermomètre
THE WATER CYCLE
This worksheet allows you to look at the water cycle in more detail. You will find a short animation
(1 minute 30 seconds) outlining the key points:
http://www.edumedia-sciences.com/fr/a88-cycle-de-l-eau
Edumedia, Cycle de l’eau
Here is an online quiz addressing the points made in the video:
http://www.edumedia-sciences.com/fr/a751-quiz-cycle-de-l-eau
Edumedia, Quiz cycle de l’eau
WEATHER FORECAST - GUIDE
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CLOUD FORMATION
This is a description of the overall mechanism behind cloud formation. For more details on the subject,
you can consult the CLOUD worksheet, where you will find the classification of different cloud types as
well as exercises. Depending on the case, the condensation and the cooling of the air are caused by
different factors. Similarly, the presence or absence of movement of air masses during their formation
will stimulate the development of the clouds and change their shapes..
Do it yourself
Warm day version. No, the bottle did not break into a sweat! The cold bottle cools down the air around
it to the point that it goes below the dew point. The excess water vapor contained in the air condenses
against the glass of the bottle.
Cold day version. Lungs contain humid air saturated with water at a temperature of approximately that
of our body (37 °C). When we exhale in a much colder environment, the air we exhale cools down to
below the dew point. The excess water vapor is condensed, forming the “mist.”
We focus on the origin of colors in the LIGHT worksheet.
This animation comes with a lesson plan as well as complementary files:
education.meteofrance.com/jsp/site/Portal.jsp?page_id=14689&document_
id=22495&portlet_id=77665
Météo France – éducation – composition de l’atmosphère – animation, Le bleu du ciel
IT’S WINDY!
Here is more information on the atmospheric circulations that create currents and influence the climates.
This chapter will give you a general idea of the causes of many climatic phenomena (rainy season, monsoon, drought, etc.).
Equatorial regions generate warm air masses that rise, creating areas of low pressure that attract hot and
humid air between the 30th parallels N and S. This forms a belt of clouds around the entire circum- ference of the Earth at the latitude where the sun is at
its zenith (adjacent photo).
A large concentration of cumulonimbus clouds
are formed in the inter-tropical convergence zone
(ITCZ), where the trade winds converge. The trade
winds are steady winds that blow from the tropics towards the equator while being deflected to
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WEATHER FORECAST - GUIDE
the west. This convergence zone
moves according to the season and
follows the dis- tribution of land and
heat sources. When the sun is at the
zenith over the Tropic of Cancer, it is
summer in the northern hemisphere
but it is also the rainy season at this
latitude. For centuries, sailors noticed
an area of calm winds (trade winds)
and its dangerous central zone that
they called the “doldrums.” Longterm changes to the ITCZ can lead to
problems in some countries, which
are either left awaiting the monsoons
in vain, or devastated by catastrophic floods.
The humid air coming from areas near
the 30th parallels N or S is drawn in by
the trade winds. In exchange, these
areas receive hot and dry air from the
equatorial region after its passage
through the troposphere. This is why
we find the world’s main deserts in
these latitudes. This is where the arid
subtropical climate prevails.
60° N
trade winds in July
30° N
ITCZ July
0°
ITCZ January
30° S
trade winds in January
60° S
Arctic Glacial Ocean
Pacific
Ocean
Atlantic
Ocean
Indian Ocean
Monsoon
Mediterranean
Equatorial
Tropical
This mechanism of air mass transfer
is called the Hadley cell. Its origin is
thermal and it exists because of the
variability of incident solar energy
depending on the latitude.
Pacific
Ocean
Oceanic
Chinese
Polar cell
60° N
Ferrel cell
30° N
The very same thermal principle is
behind the polar cells.
Ferrel cells are located in a region
between the 30th and 60th parallel
N or S. The mechanism behind them
is not thermal. Instead, neighboring
cells (polar and Hadley) force the air
circulation.
Hadley cell
0°
Hadley cell
trade winds
30° S
Ferrel cell
60° S
Polar cell
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Arid
Continental
Montainous
Polar
Between these cells, channeled winds that can be very strong, such as the jet streams, are created.
Because they are located at altitudes over 6’000 m, they were long ignored. These currents are used
by airlines to save one hour on Europe – America flights. On the other hand, they are avoided on the
return flight. Even though the Breitling Orbiter 3 extensively used air currents, the Solar Impulse pilots
will carefully avoid such strong winds, as the aircraft cannot withstand strong turbulence. Instead, it will
look for areas with calm winds: up to 110 km/h tailwind, 20 km/h headwind and 10 km/h crosswind!
Here are a few documentaries on the following subjects.
Weather and atmospheric currents:
http://www.youtube.com/watch?v=sQZlgc41_k8
C’est pas sorcier, la planète sous toutes ses latitudes
Jet streams, their discovery and their effects:
http://boutique.arte.tv/f2367-jetstreamrivieredevent
BBC - John Groom, Stephen Wilkinson, Jet Stream, la rivière du vent
This animation comes with a lesson plan as well as complementary files on the theme of atmospheric
circulation:
http://education.meteofrance.fr/lycee/animations/utiliser-les-animations-en-classe/fichepedagogique-de-lanimation-la-circulation-generale-de-latmosphere
Météo France, La machine climatique – les mouvement de l’atmosphère, Circulation générale atmosphérique
An animation sequence about the Hadley cell and jet streams can be found on the following website:
http://files.meteofrance.com/files/education/animations/circulation_generale/highres/
popup.html
Here is an online quiz addressing these different elements after summarizing the theory:
http://www.mesexercices.com/exercices/exercice-culture-2/exercice-culture-89282.php
mesexercices.com, Quiz n° 89282: Anticyclones et dépressions
Quiz
L
L
L
H
20°O
0°
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20° E
WEATHER FORECAST - GUIDE
LOCAL WINDS
The names of low altitude winds vary by region. Students could look for regional typical winds, identify
their direction on a map and state the necessary conditions for them to develop.
The main winds blowing in Switzerland are presented in Exercise 5.
IT’S RAINING, IT’S POURING
The weather disturbances that cross central Europe are caused by the struggle between polar air
masses that are set into motion by low-pressure areas in northern Europe and tropical air masses carried by the Azores high. The confrontation begins over the Atlantic on a more or less stationary front.
a) & b) The warm air mass enters an area with
polar air that it will gradually pierce, forming a
depression.
a) formation of the weather
disturbance
b) creation
of the depression area
air
movement
cold air
c) As it advances, it turns counter clockwise.
Two boundaries are formed, one in front of the
hot air supply (warm front) and the other at the
rear (cold front) forming two arms.
warm air
cold air
warm air
c) development of the disturbance
d)The weather disturbance is then developed.
The cold front overtakes the warm front (occlusion), they form a λ.
e) Both fronts disappear when the supply of hot
air is cut off from its heat source. This occurs
when the hot air mass is raised by the two cold
air masses (see figure on page 8 of the student worksheet). The air masses mix and the
two fronts are reabsorbed. The air continues
to flow through inertia but the victory goes to
the depression. It is not uncommon for several
disturbances to take place afterwards.
depression
cold air
cold air
warm front
cold front
warm air
d)
occlusion
cold air
e) weakening of
the depression
cold air
warm air
Here is a nice Météo France animation explaining the phenomenon, together with a lesson plan:
http://files.meteofrance.com/files/education/animations/perturbation_atmospherique/
highres/popup.html
Météo France, Perturbation atmosphérique : d’où vient le mauvais temps ?
WEATHER FORECAST - GUIDE
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HOW TO READ A WEATHER MAP
Synoptic weather maps display a wealth of data that we will not address here, such as the type of
clouds, pressure, rainfall intensity, etc. This is an interesting aspect that could be developed in the
context of a specific project.
Note that in the navy and the air force, wind speeds are measured in knots. The wind’s strength is
measured in Beaufort degrees. Conversion exercises are available on the worksheet « Sur mesure » :
http://www.elemo.ch/page-56959-fr.html
Exploration des eaux lémaniques (elemo), fiches pédagogiques
Quiz
With this sign, even if all the elements are not shown in detail,
students should be able to deduce that the wind comes from
the south-west and has a speed of about 25 knots.
The sky is about 75% covered with clouds.
The following program sums up the different weather events and forecasts:
http://www.youtube.com/watch?v=ldlhPV5uOjk
C’est pas sorcier, Météo : le bulletin des sorciers
Bibliography
An extensive general guide:
Pierre Kohler, Comprendre la météorologie, Hachette
A brochure summarizing common Swiss weather phenomena:
Situations météorologiques typiques dans la région des Alpes,
Office fédéral de météorologie et de climatologie
http://www.meteosuisse.admin.ch/medialib/documents/fr/broschueren.
Par.0001.File.tmp/brochure.pdf
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ALL THIS IN NUMBERS…
Exercise 1
The air currents between two high pressure areas are not very strong. On this map, there are large high
pressure bands in the North and the South. They have a thermal origin, like the Siberian anticyclone.
The Hadley cells can be located on the map. In this case, the origin of the high pressure is due to the
atmospheric circulation and not to air cooling.
H
L
L
L
H
H
H
H
H
L
H
L
H
H
H
H
H
L
L
H
L
L
L
H
Exercise 2
a) The roof area to capture the rain measures:
length ∙ width = 25 ∙ 8 = 200 m2
Volume of water which is not drained:
area ∙ amount of rainfall e = 200 ∙ 0.0336 = 6.72 m3
b) Let us calculate the amount of rain that would have fallen on Locarno in one day on an area of 1 m2:
0.0336 ∙ 1 ∙ 6 ∙ 24 = 4.8384 m3 ≈ 4,838 litres
This means that there would have been 4,838 – 414 = 4,424 more liters per square meter.
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Exercise 3
Only the rain falling in the funnel is collected. It is collected on a surface of:
π ∙ r2 = π ∙ 92 ≈ 254 cm2 = 0.0254 m2
To indicate the measurement in l / m2, you must do the following calculation:
ml read on the graduated cylinder
103 ∙ 0.0254
The numerical value is the same as the value indicated in mm.
The container will be filled when rainfall exceeds more than:
500
= 19.7 l / m2 = 19.7 mm
103 ∙ 0.0254
Continuous rainfall of 1 to 3 mm per hour is considered to be light. Moderate rain consists of 4 - 7 mm
per hour while heavy rain is 8 mm per hour and more. This implies that the container is small and it will
be easily filled. In the case of heavy rain, the container will be filled before the end of the night.
Exercise 4
Due to its high specific heat, the water in the sea, in oceans, or in big lakes has a stable temperature
during the day. Dry land heats up under the effect of the sun’s radiation. This heat input creates an
updraft, which provokes a breeze that comes from the sea.
The temperature contrast is not sufficient until the beginning of the afternoon.
On the other hand, in the evening, the shores cool quickly compared to the open ocean, where the
water temperature is relatively stable. The air contracts and creates currents directed towards the sea.
The direction of the wind is reversed. Therefore, the breeze blows towards the sea for a few hours in
the evening.
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Exercise 5
The situation C represents the “bise.” The cold polar air waves pass north of the high pressure area
(Scandinavia). Dry and temperate continental air blows over Switzerland coming from the northeast.
At times, the wind can be much stronger. This is called “black bise.” It is due to the high pressure
associated with an active depression positioned above the Mediterranean. Winds are violent and accompanied by rainfall.
The situation A represents a west wind. There is not a strong anticyclone to the west that could prevent
the passage of weather disturbances driven by the jet stream from west to east.
In the situation B, the foehn settles on Switzerland. The isobars are very tight. They highlight the large
pressure difference between the north and south of the Alps. The mountain range creates a barrier. The
air to the south of the Alps is subjected to a much higher pressure than the air to the north of the Alps.
To equalize the pressure, the air passes above the mountain range. In rising, the temperature drops
and water vapor condenses. This causes heavy rainfall on the southern slope. Once past the summits,
the dried air warms. This dry air warms at a faster rate when descending the northern slope than when
it cooled while it was wet and rising on the southern slope. It can thus contain even more water vapor
without condensing. Therefore this air is ready to absorb the moisture while rolling down the northern
side of the Alpine slopes. This dry air creates a
[°C]
[°C]
clear sky. Under the effect of the foehn, the snow
-10
-10
can melt impressively. Within hours, it can be ob∆T ≈
∆T ≈
- 6 °C / km
10
°C / km
served that temperature suddenly increases by
-4
0
more than 10°C. Depending on the orientation of
6
10
the valleys, the wind can be very strong and easily
∆T ≈
-10 °C / km 16
reach peaks of over 150 km/h.
20
{
{
The same phenomenon takes place when there is high pressure to the north and low pressure to the
south of the Alps. This is called northern foehn. This foehn effect has puzzled scientists since the 19th
century. It is common to all the mountain ranges of the world. In such a way, the “Chinook”, as it is
known in North America, was responsible for a temperature transition from -30 °C to 12 °C overnight
during the Calgary Games in 1998!
Exercise 6
Monthly rainfall records, in mm
400
As a complementary activity you could ask students to locate these cities on a map. With these
data you could discuss
the different types of climates, the fact that seasons are reversed in the
two hemispheres, etc.
300
200
Sao Paolo
100
0
Jan. Feb. Mar. April May June July Aug. Sept. Oct.
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Quebec
Geneva
Cambera
Calcutta
Tombouctou
Nov. Dec.
TECHNOLOGY: BUILD YOUR OWN WEATHER STATION!
There are innumerable devices to carry out weather measurements. Their assembly can be developed
in partnership with the professor in charge of the AC & M (manual and creative activities). The necessary material can be found in any hardware store. However, they do require the use of some tools.
Students need to be supervised while, for instance, making a hole with a drill.
THE WEATHER VANE
Weather vanes come in many shapes. They can also be painted and decorated. Students will be able to give free rein to their imagination.
If a class manufactures a large number of weather vanes, students can go
outside if it is a little windy to study how the wind blows between obstacles
such as at the corner of a building. It is then possible to map the direction
of the air currents.
Students can also manufacture a windsock, whose wire structure can be
used as a support. It can be used in a sewing project. It cannot be used to
obtain measurements but only to assess the wind direction and strength.
Céréales Killer (CC-BY-SA)
THE ANEMOMETER
For the anemometer, it will be necessary to calibrate a model during a car trip. When there is no wind,
the car will need to go at constant speed on a straight section of road. This will allow the co-pilot to
determine the number of spins of the device when the relative speed of the surrounding air will be the
car’s speed. The accuracy will be relative, but this will allow obtaining a magnitude of wind speed.
These are the results obtained for the model appearing on the photo. It consists of two sticks of 80 cm and half tennis balls. The total
mass of the movable portion is 225 g.
It is not easy to make measurements at higher speeds. Since the
axis can be shaky, the moving part could be torn by the force of
the air.
Wind speed
[km/h]
Spins
in 20s
20
4
30
8
40
12
50
16
Smaller models can be made with ping-pong balls and skewers sticks:
http://lascienceadeuxmains.com/?page_id=126
La science à deux mains, Anémomètres
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THE RAIN GAUGE
The funnel needs to be adapted to the size of the graduated cylinder or vice versa. The calibration
of the device offers an interesting geometry exercise involving several notions. For its resolution, it is
necessary to consult Exercise 3.
We are not presenting thermometer or barometer models that are often built in the context of science
lessons. There is already a student sheet on this activity, as proposed by the OCOM.
Please note that there are many models proposed in the book “Meteorology - Elements of manual creative activities (Météorologie - Eléments de l’activité créatrice manuelle)” by Beat Suter and Christian
Rohrer and published by the Swiss Society of Manual Work and School Reform.
Students must make the most of the devices they make or purchase; they can make experiments and
graphs, thus tackling the chapter on mathematical functions.
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