The Earth and Its Atmosphere:
1. Vertical structure
2. Weather and climate
Mass,Weight, Density, Pressure
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Mass M:
♦ property of matter,
♦ SI unit: kg. Other units: 1kg=1000 g, 1 lb=450 g
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W
Weight
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♦ a force, has a magnitude and direction (vector).
♦ weight = mass x gravity
g(Earth)= 9.78 m/s2
♦ SI unit: kg m/s2 -> N
g(Mars)= 3.7 m/s2
Density r:
♦ mass per unit volume: density = mass / volume
♦ SI unit: kg/m3, Other: g/cm3
Pressure p:
♦ p= force/area
♦ SI units: Pa=N/m2, Other: 1bar=100 Pa
Atmospheric pressure
Atmospheric pressure and density decrease with altitude exponentially!!!
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RECAP
Atmospheric composition:
• Permanent gases: N2, O2, Ar, Xe, Ne, H2, He
• Variable gases: CO2,H2O,O3,CH4
Greenhouse gases: H2O, CO2, NO,CH4
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• Weight.
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• The atmospheric pressure and
Mass.
Density.
Pressure.
density decrease with altitude.
Mid-chapter brief review(s)
• The
earth’s atmosphere is a mixture of many gases. In a volume of dry
air near the surface, nitrogen (N ) occupies about 78 percent and
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oxygen (O2) about 21 percent.
Water vapor, which normally occupies less than 4 percent in a volume
of air near the surface, can condense into liquid cloud droplets or
transform into delicate ice crystals. Water is the only substance in
our atmosphere that is found naturally as a gas (water vapor), as a
liquid (water) and as a solid (ice).
Both water vapor and carbon dioxide (CO2) are important greenhouse
gases.
Ozone (O3) in the stratosphere protects life from harmful ultraviolet
(UV) radiation. At the surface, ozone is the main ingredient of
photochemical smog.
The majority of water on our planet is believed to have come from its
hot interior through outgassing.
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Atmospheric pressure at any level represents the total mass of air
above that level, and atmospheric pressure always decreases with
increasing height above the surface.
Vertical Structure of the Earth’s
Atmosphere
99.9%
90%
Lapse rate
Atmospheric layers
(according to the temperature)
• Troposphere:
♦ The temperature T decreases with height at a rate of 6.5 K/km.
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♦ Well mixed as a result of turbulence and convection
♦ Weather phenomena
Tropopause:
♦ Isothermal (T constant)
♦ Located 8-15 km above the ground.
Stratosphere:
♦ The temperature T increases with height
♦ O3 layer at 25 km altitude
♦ The atmosphere is very stable
Stratopause: T=const
Mesosphere:
♦ T is decreasing with height: effective cooling through IR emission
♦ Very unhealthy region: hypoxia (oxygen deprivation), UV burns,
blood begins to boil
Mesopause: the coldest region on Earth.
Thermosphere: fast T increase. Diffusive separation of gases.
Atmospheric layers: other classifications
• Mixing:
♦ Homosphere:
well mixed,
the chemical
composition is
constant.
♦ Heterosphere:
no turbulence and
mixing,
diffusive separation
of gases
Ionization:
♦ Ionosphere: part of the
atmospheric gas is ionized
through photo ionization
or impact ionization.
♦ (talk about the atom)
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Weather/ Climate
Weather elements:
♦ Air temperature: thermometer (C, F, K)
♦ Air pressure: barometer (bar, mbar)
♦ Humidity: hygrometer (%)
♦ Wind: (m/s , km/h, mi/h)
♦ Clouds
♦ Precipitation
♦ Visibility
Weather: the daily variations of the atmospheric
conditions. “It is partly cloudy today, with a 50%
chance of rain”
Climate: average weather. “The average maximum
temperature for the month of January is 35 F.”
Weather Forecasting Using Satellites
isobar
streamline
isotherm
The World
Jupiter as seen from Cassini
Meteorology – a brief history
• Meteorology is the study of the atmosphere and its
phenomena
• In “Meteorologica” (340 B.C.) Aristotle discussed
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♦ meteors (things which fall from the sky)
♦ weather and climate, astronomy, geography…
♦ clouds, rain, snow, wind, hail, thunder, hurricanes…
Invention of weather instruments in the Middle Ages
♦ Pressure: barometer (1643, E. Torricelli)
♦ Humidity: hygrometer (1783, H. de Saussure)
Rapid exchange of weather information (telegraph, 1843)
Crude weather maps (1869)
Norwegian model of storm development (1920’s)
Air balloon and high-flying aircraft observations (1940)
High-speed computers and numerical predictions (1950-)
Weather satellites (1960-)
Aristotle
de Saussure
Simplified surface weather map
Weather phenomena: a preview
Clouds and thunderstorms
Ice storm
Tornadoes
Flooding