121 review 1

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AOS 121 Fall 2007 Environment and Society Cross-listed with IES and Geography Review for the 1st midterm exam 10/01/2007

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1st midterm: Wednesday (Oct. 3, in class) Exam time is 1:20pm~2:10pm (50 minutes) Closed book exam 30~40 multiple choice questions

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Please bring your # 2 pencil and eraser Use # 2 pencil only

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CH  01   "The Milky Way Galaxy, Solar System, and Earth’s Subsystems" CH  02    "The Physical and Chemical Structure of The Atmosphere" CH  03    "Evolution of the Atmosphere"

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On August 24, 2006, the International Astronomical Union (IAU) formally downgraded Pluto from an official planet to a dwarf planet.

“Spheres” of the Earth System: 

“Spheres” of the Earth System Atmosphere Hydrosphere (oceans, rivers, lakes, etc.) Biosphere (forests, grasslands, animals, algae, microbes, etc.) Cryosphere (mainly polar ice, glaciers) Pedosphere (soil layer) Lithosphere (rock layer) Mantle Core

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CH  01   "The Milky Way Galaxy, Solar System, and Earth’s Subsystems" CH  02    "The Physical and Chemical Structure of The Atmosphere" CH  03    "Evolution of the Atmosphere"

Composition of the Atmosphere: 

Composition of the Atmosphere Permanent Constituents (residence time ~10 – millions of years) ~ 78% of nitrogen (N2) ~ 21% of oxygen (O2) ~ 1% of argon (A) ~0.034% of CO2 Other inert gases (e.g., helium (He), neon (Ne), krypton (Kr), xenon (Xe) Variable Constituents (residence time usually a few days to a few weeks) H2O and some trace gases (such as sulfur dioxide (SO2), ammonia (NH3), nitrogen dioxide (NO2), etc. Aerosol particles - liquid droplets and solid particles Semi-permanent Constituents e.g., methane (CH4), CO, H2

Atmospheric Pressure : 

Atmospheric Pressure Most of the atmospheric gases have maximum concentration at the surface. The gas concentration usually decreases exponentially with height. But there are some exceptions (e.g., O3). The atmospheric pressure also decreases exponentially upward. This is the so-called barometric law.

Hydrostatic Balance: 

Hydrostatic Balance In the general atmosphere, the gravitational force is about as strong as the vertical pressure gradient force, so the two basically cancel each other. This is called the hydrostatic balance. But this is not true all the time. During thunderstorms, the local atmosphere can be highly non-hydrostatic.

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The traditional classification of atmospheric layers is based on temperature. We plot the air temperature versus height to see if distinct structure exists. Four layers Troposphere Stratosphere Mesosphere Thermosphere

Troposphere: 

Troposphere The lowest layer. "Tropo" means "turning" or "change". Temperature in this layer decrease with height in general. (but sometimes inversion occurs.) Strong convection causes clouds, rain, snow, thunderstorms, tornadoes, etc. The common weather phenomena are usually restricted to this layer only. Thickness of this layer varies from place to place : ~17 km near the equator and ~7 km near the pole (so characteristic thickness ~ 10 km). The top of the troposphere is called the tropopause (a temperature minimum).

Stratosphere: 

Stratosphere The temperature stays relatively constant with height initially, then increases with height, reaching a maximum (~ 280K) at height of about 50 km. Relatively calm , almost no cloud and other weather. mother-of-pearl (nacreous) clouds (mostly frozen sulfuric acid droplets) Commercial jets usually fly in the lowest stratosphere. A balloon can usually reach a maximum height near 40 km, i.e., in the stratosphere. Ozone concentration in this layer. The top is stratopause.

Mesosphere: 

Mesosphere The layer above the stratosphere is called the mesosphere. The temperature again decreases with height, reaching a minimum (~ -100C) at about 85 km (the mesopause). This is the layer where noctilucent (night-glowing) clouds may exist. We don’t understand this layer as much as other layers and not many people are studying it, either. Some atmospheric scientists call it, jokingly, the “ignorosphere”. photos by Pekka Parviainen©

Thermosphere: 

Thermosphere Above the mesosphere is the thermosphere where the temperature increases with height and can reach more than 1000 ºC. The high temperature is caused by the heating of short wave solar radiation. Will you feel cold or hot in the thermosphere? Heat and temperature are not identical things!

Are there other ways to classify atmospheric layers?: 

Are there other ways to classify atmospheric layers? Yes. For instance, we can use the influence of electric and magnetic fields. Below about 60 km the atmosphere has few free electrons, and is called the neutrosphere. Above that, the electron density and the electric conductivity increase significantly. We call this upper layer the ionosphere. At height above several earth radii, the effect of geomagnetic field becomes important. This layer is called the magnetosphere. Charged particles from the outer space become trapped in this layer and bounce back and forth between the north and south pole (and rotating with the earth at the same time) causing complicated electromagnetic phenomena (such as aurora).

The structure of Ocean: 

The structure of Ocean >0℃

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CH  01   "The Milky Way Galaxy, Solar System, and Earth’s Subsystems" CH  02    "The Physical and Chemical Structure of The Atmosphere" CH  03    "Evolution of the Atmosphere"

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Our atmosphere – abundant free oxygen--is a rarity. Large amount of liquid water ( oceans) on the surface—another unique feature in the solar system. Our present atmosphere is not a primordial atmosphere but rather a secondary atmosphere. Evolution of the Atmosphere How do we know that our atmosphere is not primordial? What is the unusual properties of our current atmosphere? Earth is very deficient of certain elements such as hydrogen and helium as compared to other parts of the solar system

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The supernova ejected pieces of heavy materials (such as nickel and iron) that reached the solar nebula and caused contractions of the gases around these heavy cores. A supernova is a stellar explosion that creates an extremely luminous object.

Formation of a proto-planetary system: 

Formation of a proto-planetary system A C D B centralized form the star eject dark (heavy) material solar nebulas

Gomez’s Hamburgera possible proto-planetary nebula: 

Gomez’s Hamburger a possible proto-planetary nebula NASA

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Secondary Origin of the Atmosphere Io, one of the Jovian (Jupiter’s) satellites Types of volcanic gases The most abundant gas typically released into the atmosphere from volcanic systems is water vapor (H20), followed by carbon dioxide (C02) and sulfur dioxide (S02).

Evolution of the Secondary Atmosphere: 

Evolution of the Secondary Atmosphere Are you saying that our atmosphere came from these volcanic gases ? Yes. What kind of gases are ejected during a volcanic eruption? Mainly H2O, CO2, SO2, Cl, N2, in that order, and bunch of other trace gases and particles. So they are really different from our atmosphere! Yes, but you have to remember that this was only the beginning. The atmosphere keeps evolving. The first to go was H2O, because the earth’s atmosphere can only hold a small amount of water vapor (the saturation value). The excess water vapor would condense and precipitate (rain)  Oceans! The rain water also dissolved CO2 SO2, and Cl (which would eventually form NaCl—remember the ocean water is salty?). N2 became the dominant gas in our atmosphere mainly because of its low water solubility! Nice story, but where is O2 ? In the early atmosphere, there was little free oxygen. It was even slightly reducing. This is in fact beneficial for life to form, as the primitive lives would have difficulties to survive in an oxidizing atmosphere. Under this reducing environment, life forms evolved and finally green plants appeared. The chlorophylls in green plants make the photosynthesis possible. During this process (in the presence of sunlight, of course) oxygen is released. Eventually the atmosphere would accumulate about 20% of free oxygen (so aerobic life forms can survive!). The appearance of O2 also made the formation of O3 possible which further shields solar UV and protects life forms on the earth surface.

Venus, Mars, and EarthSimilarities and Differences: 

Venus, Mars, and Earth Similarities and Differences So, they are similar in size and density, but very different in the distance from the sun.

But the atmospheres of Venus and Mars are very different from the earth’s atmosphere.: 

But the atmospheres of Venus and Mars are very different from the earth’s atmosphere. Venusian atmosphere – CO2 (~96.5%), N2(~3.5%), Psurface~ 90 bar (the pressure 900 m under sea), sulfuric acid clouds Earth atmosphere – N2(~78%), O2(~21%), Ar(~1%), Psurface~1 bar, water clouds Martian atmosphere – CO2(~95%), N2(~3%), Ar(~1.6%), Psurface~0.006 bar (very thin atmosphere), dry ice clouds If the inner planets have evolved similarly, how come their atmospheres are so different?

Evolution of Venus Atmosphere: 

Evolution of Venus Atmosphere The initial (secondary) chemical composition was similar to earth’s atmosphere. No condensation of water vapor to form liquid water due to the runaway greenhouse effect. Water vapor were most likely photo-dissociated by solar radiation and either escaped from the atmosphere or chemically combined with other substances. All because Venus is too close to the sun! Evolution of Mars Atmosphere Smaller planet, smaller atmosphere ( P sfc ~ 0.006 bar) Farther away from the sun, hence colder T ~ 218K or –55C). Cold atmosphere cannot hold large amount of water vapor. There was no liquid water to dissolve CO2 and hence CO2 became the dominant gas.

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1st midterm: Wednesday (Oct. 3, in class) Exam time is 1:20pm~2:10pm (50 minutes) Closed book exam 30~40 multiple choice questions Please bring your # 2 pencil and eraser Use # 2 pencil only