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Midterm

Midterm Notes


Department
Atmospheric & Oceanic Sciences
Course Code
ATOC 181
Professor
Daniel Kirshbaum
Study Guide
Midterm

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1: THE EARTH AND ITS ATMOSPHERE
The Atmosphere
- atmosphere: the envelope of gases that surround a planet and are held to it by the planet’s gravitational
attraction
o 99% of mass is confined to a layer of 0.25% earth’s radius
o shields humans from ultraviolet radiation
o essential for like (H2O, O2, CO2)
- nearly 150 km separates sun & earth, yet solar radiation drives the earth’s weather
- origin
o earth born ~ 4.6 billion years ago
o ‘outgassing’ of lava, ashes & gases erupt from volcanoes supplying H2O, CO2 & N2 forming the
atmosphere bound to earth by gravitational field & mass
o traps heat & causes planet to warm
average global temperature was probably between 85-110 °C, now 15 °C
o planet cooled
water vapour condensed to form clouds/rain
formation of oceans
CO2 stored in oceans & deposited into sedimentary rocks
N2 begins to dominate
o life formed ~ 2 billion years ago
photosynthesis produce O2
through photochemical reactions, O3 shield form
o now main atmospheric constituents are N2 (78%) and O2 (21%)
H2O ranges from 0-4% (0 in poles, 4 in tropics)
trace amounts of CO2, O3 & other gases
aerosol particles
Ozone, O3
- 97% in upper atmosphere where it forms naturally
- ozone shields earth from ultraviolet radiation
- layer being depleted near poles by chlorofluorocarbons (CFCs) from spray cans & refrigerants
- at surface, primary ingredient in photochemical smog
o irritates eyes & throat; damages vegetation
Carbon Dioxide, CO2
- used by plants for photosynthesis to produce oxygen
- absorbs portion of earth’s outgoing radiation & radiates it back to earth (greenhouse gas)
- concentration increasing rapidly
Water Vapour, H2O
- produced by evaporation/sublimation
- lost by condensation/deposition (part of hydrologic cycle)
- condenses to form clouds

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- stores latent heat released in thunderstorms & hurricanes
- critical global circulation factor
- highly effective greenhouse gas
- initially water vapour produced by volcanoes, then evaporation of liquid & sublimation of ice contributes
to formation of water vapour
Air
- mass: the amount of matter/material in the ample volume
- density: the concentration of mass; mass ÷ volume; ie/ kg/m3
- mass & density profiles
o both tend to decrease rapidly with height but density may be relatively uniform in well-mixed
layers
o air density decreased with height because the heavier particles of air descend
- weight: the force exerted by the mass due to gravity; mass x gravitational acceleration; ie/ kg m/s2)
- pressure: the weight of the overlying air column; force per unit area; Pa = Newtons/m s2; don’t feel it
because it acts in all directions; body’s internal pressure adjusts to atmosphere, so there is no pressure
difference
- density & pressure profile
o decrease with increasing altitude
- layers of the atmosphere
o spheres: layers
o pauses: boundaries between layers
o troposphere
surface up to ~ 12 km
temperature decreases with height: ~ 6.5°C/km
where weather occurs
thunderstorm clouds often reach the tropopause
o stratosphere
temperature initially isothermal (constant) then increased with height up to ~ 50 km
site of ozone layer
may impact weather over seasonal time scales
o mesosphere
temperature decreased with height up to ~ 80 km
o thermosphere
temperature increases with height
o homosphere: well mixed “lower” atmosphere
8% N2, 21% O2
o heterosphere: poorly mixed “upper” atmosphere
o ionsphere: electrically charged region with ions & free electrons
plays major role in radiocommunications since it reflects AM signals, allowing
transmission over large distances
D region absorbs radio waves, weakening surface signal; much stronger during daytime
due to photoionization

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Instruments
- radiosondes: small instrument package carried by helium balloon equipped with a radiotransmitter
which transmits information to a service station on temperature, air pressure and humidity
- rawindsondes: a radiosonde which includes winds
2: ENERGY: WARMING THE EARTH AND ITS ATMOSPHERE
Energy
- energy: the capacity to do mechanical work on some object or fluid; units: Kg m2 s-2 (Joules)
- work: the motion of an object or fluid resulting from an applied force
- kinetic energy
o about objects/fluids in motion
o ½ mv2 (m = mass measured in kg; v = wind speed measured in metres/second)
- gravitational potential energy
o PE = mgh (g = gravitational acceleration measured in m/s2; h = height measured in metres)
- internal energy
o the collective microscopic kinetic & potential energy of the molecules in a substance
o action controls temperature/air
o not all that different from kinetic, just microscopic
- radiant energy
o vibrations of charged particles within atoms (electrons & protons) generate electromagnetic
fields
o every object with a temperature is emitting electromagnetic radiation
- conservation of energy
o 1st law of thermodynamics: energy can’t be created nor destroyed, it merely changes form
o heating to system must be balanced by work and/or increase in internal energy
o without external heating/cooling, work is balanced by changes in internal energy (adiabatic
processes)
Temperature
- temperature: measure of the kinetic energy of the atoms & molecules within a substance; measured in
°C, °F and K
- absolute zero: 0 K = -273 °C = -459 °F is the coldest temperature possible; molecular motion ceases
- molecules move faster as temperature increases; molecules move slower as temperature decreases
Heat
- heat: energy in transit from a hot body to a cold body and then stored as internal energy
- calorie: units for heat; energy needed to heat 1g of H2O by 1°C; Joules = 0.239 cal
- specific heat
o heat capacity: ratio of heat added to a substance to its corresponding temperature
o specific heat capacity: amount of heat required to raise the temperature of 1g by 1°C
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