Transcript Introduction - San Jose State University

MET 112 - Lecture 3
Radiation Continued
Dr. Craig Clements
San Jose State University
Scattered and reflected light
When solar radiation enters the atmosphere, a number of
Interactions take place
Some energy is absorbed (by ozone in stratosphere) and
some is deflected.
When sunlight strikes very small objects, such as air
molecules and dust particles, the light itself is deflected in
all directions– forward, sideways and backwards.
The distribution of light in this manner is called Scattering.
Because air molecules are much smaller than the wavelengths
of visible light, they are more effective scatterers of the shorter
(blue) wavelengths than longer (red) wavelengths.
Fig. 2-13, p. 40
Fig. 2-14, p. 40
Fig. 2-14, p. 40
Scattering gives us our blue sky
…and reddish sunsets and sunrises.
Scattered and reflected light
Sunlight can be reflected from objects.
Generally, reflection differs from scattering in that during
the process of reflection more light is sent backwards.
Albedo is the percent of radiation returning from a given
surface compared to the amount of radiation initially
striking that surface.
Table 2-2, p. 41
Fig. 2-15, p. 41
Albedo Field Experiment: Report Due TBA

We are going to measure the albedo of different
surfaces at SJSU.

Your report should explain:
1. What we did.
2. How and with what?
3. Measurement results
4. Explain what surface should absorb more
energy.
You will need to take notes during this experiment.
Why do we have seasons?
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Seasons
Why do we have seasons?
Seasons are regulated by the amount of solar
energy received at the earth’s surface.
This amount is determined by the angle at which
sunlight strikes the surface and by how long the
sun shines on any latitude (daylight hours).
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 Insolation – Incoming solar radiation
 Solstice –
day of the year when the sun shines
directly over 23.5°S or 23.5°N
 Equinox –
days of the year when the sun shines
directly over the equator
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Fig. 2-18, p. 43
Sun angle
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Sun Angle
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Sun angle (2)
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Notice the angle of tilt of the earth’s axis.
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March
June
Sept.
Dec.
What influences incoming solar
energy?
 The Sun’s angle of incidence:
– Lower sun angle, less incoming energy
– Higher sun angle, more incoming energy
 Length of time the Sun shines each day:
– Summer season, more sun hours
– Winter season, less sun hours
• These are caused by the tilt of the earth’s axis
• The earth’s axis points to the same direction in space all
year long.
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Fig. 2-24, p. 50
What month do you think this graph represents?
a) December b) March c) June d) September
Answer: December
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Earth’s energy: latitudinal
perspective
 A majority of the sun’s energy enters the Earth
system in the tropics.
 The tropics thus becomes quite warm, while the
poles relatively cool.
 The atmosphere attempts to bring the tropics
and high latitude into equilibrium
– Weather systems ultimately act to bring
warm air to higher latitudes and cold air
to lower latitudes.
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On June 21st, at what latitude is the sun
directly overhead at noon?
1.
2.
3.
4.
5.
Equator (0)
23.5°N
23.5°S
90°N (north pole)
90°S (south pole)
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How many hours of daylight are present
at the South Pole on February 20th?
1.
2.
3.
4.
5.
0 hours
6 hours
12 hours
18 hours
24 hours
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On September 22nd, at what latitude is
the sun directly overhead at noon?
1.
2.
3.
4.
5.
Equator (0)
23.5°N
23.5°S
90°N (north pole)
90°S (south pole)
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Where would you expect to have longer days;
45 ° N on June 21st or 50°S on Dec 21st?
1.
2.
3.
4.
45°N
50°S
They are the same
Impossible to tell
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Seasons Review
 A season is one of the major divisions of the year,
generally based on yearly periodic changes in weather.
 In temperate and polar regions generally four seasons
are recognized: spring, summer, autumn (fall), and
winter.
 In some tropical and subtropical regions it is more
common to speak of the rainy (or wet, or monsoon)
season versus the dry season, as the amount of
precipitation may vary more dramatically than the
average temperature.
 In some parts of the world, special "seasons" are
loosely defined based upon important events such as a
hurricane season, tornado season or a wildfire
season.
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