Download Weather Forecasting

Weather
2
Table of Contents
What are Weather and Climate? ............................................................................................................................................ 3
Characteristics of the Atmosphere ......................................................................................................................................... 3
Atmospheric Pressure ............................................................................................................................................................. 4
Layers of the Atmosphere:...................................................................................................................................................... 5
Lab: What percent of the atmosphere is oxygen? ..................................................................................................... 7
Homework Assignment #1: ..................................................................................................................................................... 9
Factors that Affect Climate: .................................................................................................................................................. 10
Air Masses ............................................................................................................................................................................. 11
Homework Assignment #2 .................................................................................................................................................... 12
Homework Assignment #3: ................................................................................................................................................... 14
Winds .................................................................................................................................................................................... 16
Humidity................................................................................................................................................................................ 18
Homework Assignment #4: ................................................................................................................................................... 19
Greenhouse Effect ............................................................................................................................................................. 20
Greenhouse Effect Lab: .................................................................................................................................................. 20
Weather Forecasting............................................................................................................................................................. 21
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What are Weather and Climate?
Weather is the state of the atmosphere at a given time and place. Weather changes continuously, but it is still possible
to determine an average weather for a location. The average weather at a location is called climate, and it is based upon
many observations over many years.
Characteristics of the Atmosphere
Atmosphere – layer of gases that surrounds Earth
Gases in the atmosphere:
 78% N2 – kept constant by the N2 cycle
 21% O2 – kept constant by the O2-CO2 cycle
 0.9% Ar
 0.1% other, including CO2, O3, & H2O (which can vary to as much as 4%)
water, carbon
dioxide, other
1%
oxygen
21%
Particulates:
nitrogen
78%
 Volcanic dust
 Ash from fires
 Microscopic organisms
 Minerals lifted from soils by winds
 Pollen
 Meteorite particles
 Salt tossed into air from sea spray
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Atmospheric Pressure
Atmospheric Pressure is the force per unit area that is exerted on a surface by the weight of the atmosphere
Atmospheric pressure decreases with altitude.
Standard Atmospheric Pressure
=
1 atmosphere
=
760 mm of mercury
=
1000 millibars
=
average atmospheric pressure at sea level
barometer – instrument used to measure atmospheric pressure
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Layers of the Atmosphere:
The atmosphere is divided into layers.
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1. troposphere – closest to Earth’s surface
- weather
- temperature decreases as altitude increases (Earth’s
surface provides some thermal energy)
2. stratosphere
- jet stream – moves weather
- ozone layer
- temperature increases as altitude increases (heated by
absorption of solar radiation by ozone)
In
3. Mesosphere
- temperature decreases as altitude increases
- meteors burn up in the mesosphere
4. Thermosphere
- temperature increases as altitude
increases (nitrogen and oxygen absorb
solar radiation)
- ionosphere (lower region of thermosphere) – auroras
- exosphere
this graph, the temperature in each of the layers
is
compared:
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Lab: What percent of the atmosphere is oxygen?
Purpose: To determine what percentage of the Earth's atmosphere is oxygen.
Materials:
Birthday candle
100ml Graduated cylinder
penny
safety goggles
foil pan
matches
large test tube
water
Glass marking pencil
Safety Procedures: Remember to ALWAYS wear your safety goggles during this lab! Use caution
when lighting the candle for the experiment.
Procedure:
1. Light the candle and let a few drops of wax fall on the penny. Blow out the candle. Stand
the candle on the melted wax.
2. Fill the test tube with water. Using the graduated cylinder to measure this volume of
water (to the nearest milliliter) and record it on the DATA TABLE in the space called
volume of air in the test tube.
3. Pour the water into the foil pan, place the penny and the candle into the center of the
beaker. The penny should be upright.
4. Light the candle. Rapidly invert the test tube over the lighted candle. Don’t allow the
test tube to touch the candle as it is passing over it. Make sure that the open end of the
test tube is underneath the water’s surface but not touching the bottom of the foil pan.
5. As the candle uses the oxygen in the test tube the candle will go out. Water will be
drawn into the tube to replace the oxygen that the candle used.
6. When the candle goes out, mark the level of the water that's in the test tube with the
marking pencil. Remove the tube from the water.
7. Fill the test tube with water to this line. Measure the volume of water and record. The
volume is the volume of air in the test tube minus the oxygen that the candle used.
8. To find the volume of oxygen in the test tube, subtract the volume of air after the
candle goes out from the original volume. Record on the DATA TABLE.
9. Determine the percentage of oxygen in the air by using the following formula: (record
all data)
% of oxygen in the air = volume of oxygen in test tube
x 100
volume of air in test tube at start
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Data Table:
Volume of Air in the test tube at start
Volume of air in test tube after candle goes out
Volume of oxygen
Percentage of Oxygen in the air
Class Data Table:
Experiment
% oxygen calculated
(average of all groups
performing experiment)
Large candle, large test tube
Small candle, large test tube
Large candle, small test tube
Small candle, small test tube
Analysis Questions: Please answer these questions in your lab book.
1. Would the same result for percentage of oxygen in the air be obtained if a larger test tube were
used? Why or why not?
2. Would the same result for percentage of oxygen in the air be obtained if a larger candle were
used? Why or why not?
3. Why does the water in the test tube rise as the candle goes out?
4. Nitrogen is the other major component of the air (78.1%) What property of nitrogen have you
discovered as a result of this experiment?
5. How much oxygen would be present in 5 L (5000 mL) of air? Show your work!
6. How does your experimental data compare with the actual percentage of oxygen in the
atmosphere? What are some sources of error that may explain why your results weren’t exactly
as predicted?
7. Based on your observations, what is an effective method for putting out a small fire?
8. How does the size of the candle affect the experiment?
9. How does the size of the test tube affect the experiment?
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Homework Assignment #1:
Use your notes to complete these matching questions. Write the letter of the correct response from the last column on
the line in front of the phrase in the first column.
_______
instrument used to measure atmospheric pressure
A.
Atmospheric Pressure
_______
Bands of glowing gas that occur in the
thermosphere when it is bombarded by energy
from the Sun
B.
Jet stream
_______
Standard Atmospheric Pressure
C.
stratosphere
_______
force per unit area that is exerted on a surface by
the weight of the atmosphere
D.
barometer
_______
The two most important gases in the atmosphere
by volume
E.
Mesosphere
_______
Layer of the atmosphere closest to Earth’s surface
F.
aurora
_______
The high velocity winds in the stratosphere that
move weather
G.
troposphere
_______
layer of the atmosphere where meteors burn up
H.
Nitrogen and oxygen
_______
Location of ozone layer
I.
thermosphere
_______
The two most important ways that particulates are
added to the atmosphere
J.
760 mm of mercury
_______
The farthest layer of the atmosphere
K.
Volcanoes and fires
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Factors that Affect Climate:
1. Latitude - Regions of the earth closer to the equator receive the most direct solar radiation and therefore are
warmer. Latitude (distance north or south of the equator) affects climate.
North Pole – 66.5oN to the North Pole
Temperate Zone – 23.5oN to 66.5oN
Tropics – 23.5oN to 24.5oS
Temperate Zone – 23.5oSto 66.5oS
South Pole – 66.5oS to the South Pole
2. Bodies of water – Water heats up and cools down more slowly than land does. Therefore, large bodies of water
affect the climate of coastal areas by absorbing or giving off heat. Coastal regions are warmer in the winter and
cooler in the summer than inland areas at similar latitude.
3. Ocean Currents – Warm currents from the equator that flow toward higher latitudes warm the land regions they
pass.
4. Mountains – At the same latitude, the climate is colder in the mountains than at sea level. The atmosphere is
thinner at higher altitudes so the air in the mountains has fewer molecules to absorb heat.
5. Cities – The temperature in cities can be several degrees warmer than the temperature of nearby rural areas.
This is called the heat island effect. Cities contain asphalt which heats up rapidly and absorb a lot of energy from
the Sun. Rural areas covered with vegetation stay cooler because plants and animals contain water which heats
up more slowly.
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Air Masses
Air mass – a large body of air with uniform temperature and moisture content
Front – the boundary between air masses of different densities
Cold front – the place where a cold air mass and a warm air mass meet; produces quick storms
clouds, rain, snow when a cold air mass overtakes a warm air mass
- the moving cold air lifts the warm air (clouds will form if the air is moist)
- short lived and sometimes violent storms
Warm front – the place where a warm air mass moves toward and over a slower mass of cold air;
steady rain or snow; warm air rises over the cooler air; precipitation over a large area
Stationary front – a front that either moves very slowly or not at all ; the place where two air masses
meet but neither is displaced; steady rain or snow
Occluded front – fast moving cold front overtakes a warm front and lifts it off the air completely
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Homework Assignment #2
Read this information about barometers and answer the questions that follow.
Water-based barometers
This concept of "decreasing pressure means bad weather" is the basis for a primitive weather prediction
device called a weather glass or thunder glass.
It consists of a glass container with a wide spout. The container is filled with water up to about the middle
of the spout; some air is left in the main body of the container. The design is such that the air pressure of
the air pocket inside the device is higher than the outside, it will push some of the water up the spout. If
the air pressure outside is low enough, some of the water may even drip out of the spout. These devices
are essentially a water-based version of the mercury barometer.
Mercury barometers
A standard mercury barometer has a glass column of about 30 inches (about 76 cm) in
height, closed at one end, with an open mercury-filled reservoir at the base. Mercury in
the tube adjusts until the weight of the mercury column balances the atmospheric force
exerted on the reservoir. High atmospheric pressure places more downward force on the
reservoir, forcing mercury higher in the column. Low pressure allows the mercury to drop
to a lower level in the column by lowering the downward force placed on the reservoir.
The first barometer of this type was devised in 1643 by Evangelista Torricelli. Torricelli had set out to
create an instrument to measure the weight of air, or air pressure, and to study the nature of vacuums.
He used mercury because it is denser than water. To create a vacuum with water takes a column over 30
feet long, while with mercury it takes less than three feet.
Torricelli documented that the height of the mercury in a barometer changed slightly each day and
concluded that this was due to the changing pressure in the atmosphere.
The mercury barometer's design gives rise to the expression of atmospheric pressure in inches or
millimeters: the pressure is quoted as the level of the mercury's height in the vertical column. 1
atmosphere is equivalent to about 29.9 inches, or 760 millimeters, of mercury. The use of this unit is still
popular in the United States, although it has been disused in favor of SI or metric units in other parts of
the world. Barometers of this type can usually measure atmospheric pressures in the range between 28
and 31 inches of mercury.
Aneroid Barometers
Because mercury barometers can be expensive, barometers without fluid (aneroid) were invented. They
are less precise, but also less costly and fragile than mercury barometers.
T he aneroid barometer is operated by a metal cell containing only a very small amount of air, or a series
of such cells joined together. Increased air pressure causes the sides of the cell or cells to come closer
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together. One side is fixed to the base of the instrument while the other is connected by means of a
system of levers and pulleys to a rotating pointer that moves over a scale on the face of the instrument.
The aneroid barometer (above) consists of a closed
sealed capsule with flexible sides. Any change in
pressure alters the thickness of the capsule. Levers
magnify these changes, causing a pointer to move on a
dial, or numbers to change on a digital read-out device.
Questions –
1. How are water based barometers, mercury barometers, and aneroid barometers similar?
2. How are water based barometers, mercury barometers, and aneroid barometers different?
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Homework Assignment #3:
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Winds
Purpose: To draw Earth's Planetary Wind Belts by carefully following a precise set of directions.
Materials:
Ruler
Colored Pencil
Procedure:
1) On the circle below, connect the tick-marks on both the left and right sides of the "Earth” with a
pencil and ruler.
2) In the right margin of your paper label the lines with the following latitude numbers:
Oº, 30º N, 30º S 60º N, 60º S, 9Oº N,
9Oº S
3) Write the word "LOW" directly
on the line representing the
equator.
This identifies the equator as an
area of warm low pressure.
4) Using the words "High" and
"Low", continue identifying the
rest of the latitude lines you drew
on your circle.
Alternate the words, beginning at
the Equatorial Low, then working
your way both North,
then South, towards each pole.
5) Draw 3 arrows in each of the 6
sections on your globe.
Make the arrows point from lines
representing high {Cold} areas to
low {Warm} areas.
6) Now, using a colored pencil,
deflect each of the arrows to show how Earth's rotation
would affect wind direction. Remember: winds are deflected to the right in the Northern Hemisphere
and to the left in the Southern Hemisphere.
Hint: Look DOWN the arrow TOWARDS the point and then deflect it in the appropriate direction.
7) Using the names that appear below label each of the 6 sections containing deflected arrows to
identify that region as one of Earth's "wind belts".
Write the label within each different section on the circle.
Remember: Winds are named according to the direction FROM WHICH they come.
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· Polar easterlies(Northern and Southern Hemispheres)
· Northeast tradewinds
· Southeast tradewinds
· Prevailing (South)Westerlies
· Prevailing (North)Westerlies
8) Use a colored pencil to indicate where the "mean position of the Polar Jetstream" is
for both the Northern and Southern Hemispheres.
9) On the right side of your globe, draw a Convection Current showing the pattern of air flow
be PLANETARY WINDS LAB QUESTIONS
Place your Answer to the following questions on the "Answer Sheet" on page 4.
1) The deflection of wind, ocean water and objects flying through the air is known as the:
__________________ ___________________.
2) This deflection is caused by: ______________________ ___________.
3) What causes "winds"? _______________________________________________________ .
4) On a molecular level, explain why cold air is heavier, (denser) and therefore,
exerts more pressure than warm air.
5) Why then do winds blow from areas of cold, high pressure to areas of low, warm pressure?
6) Describe the air mass characteristics (temperature and humidity), for each of the following:
a) the equatorial low(0º): ___________ & ___________
b) the 30º N & 30º S subtropical highs: ________ & _______
c) the 60º N &60º S subpolar lows: ___________ & _________
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Humidity
SPECIFIC HUMIDITY – the amount of water vapor in the air
RELATIVE HUMIDITY – the ratio of the air’s specific humidity compared to
its potential humidity at that temperature
Temperature Amount of water
(oC)
vapor the air can
hold (grams of
water per kg of air)
0
3.5
10
7
20
14
30
26.5
The relative humidity of air changes if….
- water is added or taken away
- temperature of the air is changed
PSYCHROMETER – instrument used to measure relative humidity
HYGROMETER – instrument used to measure humidity
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Homework Assignment #4:
1. What is the relationship between temperature and the capacity of air to hold water vapor?
2. How is relative humidity different from absolute humidity?
3. Referring to this
chart, when is
relative humidity
highest during a
typical day?
4. Referring to the
chart in the
previous question,
when is relative
humidity lowest
during a typical day?
5. Referring to the chart in the previous question, when is dew most likely to form?
6. How are air temperature and relative humidity related?
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Greenhouse Effect
Solar radiation hitting the earth is absorbed by the atmosphere and heats the planet. This is called the greenhouse
effect.
Over the past 100 years, the average global surface temperature on Earth has increased by about 0.6oC. This increase
is known as global warming. Some researchers believe that this is due to an increase in CO2 over the past 100 years as
a result of increased combustion.
Greenhouse Effect Lab:
Purpose: To determine the effect of a transparent or semitransparent covering on the temperature of
air.
Materials:
1 empty plastic soda bottle (two-liter size) with a cap
a nail
two thermometers
Procedure:
1. Using the nail, make a hole near the top of the plastic bottle. Place one of the thermometers in the
hole. Both thermometers and the bottle should be outdoors on the ground in full sunlight.
2. Place the other thermometer outside the bottle, next to it on the ground. Be sure that both
thermometers are receiving the same amount of sunlight.
3. What happens? Do both thermometers register the same temperature? If not, which one is higher?
Why?
Data:
Present your data in a chart comparing the temperature in the two locations.
Analysis:
Prepare a three paragraph explanation that describes not only what happened, but why it happened,
citing your data and your research into the greenhouse effect.
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Weather Forecasting
Weather models are one of the main tools forecasters now use to help predict the weather. There are
many types of models, including numerical models. These models are comprised of a certain number of
mathematical equations that represent the behavior of a physical system, such as the atmosphere.
Beginning in the 1950’s, the National Weather Service (NWS) began to utilize some of the early
versions of computers to make large-scale weather forecasts using numerical models. Since that time,
computers have become faster and increasingly complex and sophisticated, and their ability to provide
more accurate forecasts has also improved
A barometer is commonly used for weather prediction, as high air pressure in a region indicates fair
weather while low pressure indicates that storms are more likely. Simultaneous barometric readings from
across a network of weather stations allow maps of air pressure to be produced.
As a general rule, if the barometer is falling then bad weather or some form of precipitation will fall,
however if the barometer is rising then there will be nice weather or no precipitation.
If the wind comes from these
directions
And the air pressure is
you should predict
East, NE, or N
Low, falling fast
Windy with heavy rain or snow; clearing after
24 hours
S, SE or E
Low, falling fast
Windy with heavy rain, or snow changing to
rain, clearing within 24 hours
S or SW
Low rising slowly
Clearing, fair for 2-3 days
Shifting to W
Low, rising fast
Storm ends, clearing and colder
SE, E or NE
Falling slowly
Rain/snow starting soon, lasting 1-2 days
E or NE
Falling slowly
Rain/snow within 24 hours
SE, E, or NE
Falling fast
Rain/snow within 12 hours, clearing in 36
hours
SW, W or NW
High, rising fast
Fair, then warmer with rain/snow in 2 days
SW, W, or NW
High, rising slowly
Fair, little change in temperature for 1-2 days
SW, W or NW
High, falling slowly
Fair, with slowly rising temps for 1-2 days