Transcript 1aIntro to Weather

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Chapters 14-18: The Atmosphere
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Atmosphere….
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What is “weather”?
The state of the atmosphere at any given time
What is “climate”?
A generalized description of weather conditions in
a region over a period of time
What is “meteorology”?
The science of studying Earth’s atmosphere and
weather
What is “atmosphere”?
The envelope of air (gasses) that surrounds the
earth; one of the four “spheres” of the earth
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• The most important basic elements of weather
that are measured are: air temperature,
humidity, type and amount of cloudiness, type
and amount of precipitation, air pressure, and
speed and direction of wind
• Air is a variable mixture of components, mainly
nitrogen and oxygen with small components of
other gases such as argon; there is also a very
small amount of carbon dioxide that is critical
to the atmosphere
• Air also contains water vapour; although it is a
relatively small amount, it, too is very important
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Air also contains aerosols: very fine solid and
liquid particles such as sea salt, smoke, soot, soil,
pollen, volcanic ash and dust, chemicals, bacteria,
and other pollutants
Aerosols are important in the formation of clouds
and fog, in blocking and absorbing sunlight, and in
scattering light at sunrise and sunset; they also
contribute to pollution such as smog
Ozone (O3) is a form of oxygen different from what
we breathe (O2), and high in the stratosphere
forms a protective layer that shields Earth from
much of the harmful UV (ultraviolet) radiation from
the Sun
Ozone is broken down in the presence of
chlorofluorocarbons (CFCs), which used to be
used as propellants in aerosol cans
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Ozone at the surface of the Earth is considered a
pollutant
About 50% of Earth’s atmosphere is within 5.6 km
(3.5 miles) of the surface of the Earth, about 90%
is within 16 km (10 miles) and 99.99997% is within
100 km (62 miles)
Air pressure, the weight of air pressing down, is
highest at sea level and decreases with altitude
The atmosphere is divided into layers based on
temperature changes
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Figure 1: Structure of the Atmosphere
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Thermosphere – temperatures rise
(mesopause)
Mesosphere – temperatures drop
(stratopause) – temperatures rise to this point
Stratosphere – strong steady winds & weather
(tropopause) – temperatures drop to this point
Tropopause – weather occurs here
Ionosphere –
layer of
ionized
particles
makes radio
wave
transmission
possible
Ozonosphere
layer of
ozone
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The Sun is the source of nearly all the energy that
drives Earth’s weather (and climate, even though
the amount of the Sun’s radiation intercepted by
Earth is very small)
The surface of the Earth is not heated equally; this
drives ocean currents and creates winds that
attempt to redistribute heat from the warm
equatorial areas to the cool polar areas
The rotation (spinning of Earth on its axis) and
revolution of Earth (around the Sun), as well as
the fact the Earth is a sphere all have an impact
on how solar radiation is received on the Earth
The angle of incoming solar radiation changes
throughout the seasons of the year
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Heat is transferred in the atmosphere by
Conduction: heat is transferred by collisions
between molecules – not very important in the
atmosphere
Convection: heat is transferred by circulation in
fluids – this is critical in the atmosphere
Radiation: heat is transferred as a wave – this is
how solar energy reaches Earth; different
wavelengths exist, such as visible light, infrared
radiation, and ultraviolet radiation
Temperature is a measure of the energy of
molecules
A thermometer is used to measure temperature
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Temperature can be affected by different factors;
latitude (distance from the equator) is a major factor
controlling temperature, but it is not the only factor:
Differential heating of land and water: land heats up
more rapidly and to higher temperatures and cools
more rapidly and to cooler temperatures than water
Altitude: higher elevations generally experience
lower temperatures than lower elevations
Proximity to the sea: areas closer to the sea
generally experience less variation in temperature,
and areas far away from the sea generally
experience more extreme variation in temperature
Cloud cover: during the day, clouds tend to reflect
incoming radiation, leading to cooler temperatures
than if the sky was clear; at night, clouds tend to trap
heat , leading to warmer temperatures than if the sky
was clear
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Read “World Distribution of Temperature” on p. 399-400,
and examine the figures shown:
Figure 2a: World average temperatures in January
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Figure 2b: World average temperatures in July