1. Energy: The Fuel for the Atmosphere (Text Pg 25-42, Pg 52-57)
Learning Outcomes:
Describe how energy is transferred as heat in the atmosphere.
Describe the factors involved in the balance of energy and how this determines the temperature.
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2. Energy Energy: conserved, Kinetic: energy of motion or
Potential: energy not yet used)
can be transferred
Heat: energy transfer from one object to another due to the difference in temp between them.
Direction: high energy to low energy (hot to cold)
Sun: energy source
Earth: uneven energy distribution (poles vs equator): transfer energy via ocean and atmospheric transport – Wx and currents
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3. Temperature and Density
average speed of atoms and molecules (Figure 2.1)
Celsius: 0 (water freeze pt), 100 C (boiling pt)
Absolute: Kelvin (0 K) K = C + 273
warm air, less dense (perfect Gas)
cold air, more dense
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4. Energy Storage: Heat Capacity (pg 70)
different substances: different capacities to store energy
Specific Heat (energy required to raise the temp of 1 g of substance 1 C)
Rock = 0.2 (cal/g x C)
Water = 1.0 (cal/g x C)
water requires 5 times more energy input than rock to raise its temperature 1 C.
to cool 1 C, water requires 5 times more energy lost to the surroundings than rock
water/land interface: large temperature differences for same energy input or loss
moderating effect of water body on climate.
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5. Heat Transfer in Atmosphere
Direction: Hot to cold
Rate of Transfer: depends on temp difference – rate greater for greater difference
Conduction : Heat transfer by direct contact of air molecules
still air: poor conductor, water 30x better, silver 18,000x better
Convection : Heat transfer vertically by vertical movement of warm air (less dense: rises)
(Advection): horizontal transport of heat and other properties by wind
Radiation : Heat transfer via Electromagnetic Energy
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6. Convection: Thermal Cell (Figure 2.6)
Convective circulation or thermal cell
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7. Other Heating/Cooling Processes: Phase Change of Water – Latent Heat
Latent Heat: heat energy required to change a substance, such as water, from one state to another
“Latent” : hidden heat (cannot be sensed) vs. Sensible Heat (heat that can be sensed: thermometer)
heat energy is required or released when H2O undergoes a phase change (ice, liquid, vapour)
example: evaporation: requires heat energy (600 cal/g): taken from surroundings (if available) becomes latent (or locked up in water vapour molecules): surrounding air cools
example: condensation: heat energy latent in water vapour now released to surroundings (600 cal/g): latent heat appears as sensible heat (can be sensed): surrounding air warms
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8. Heat energy absorbed and released (Figure 2
Heat energy absorbed and released (Figure 2.3) Note terms used to describe phase change Figure 2.4 Latent Heat release with condensation: important in cloud vertical development (inside of cloud warmer than surroundings
See video:
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9. Other Heating/Cooling Processes: Expansion/Compression (Figure 1 pg 33)
Drop in pressure with height means that as:
Parcel of air rises, it expands and cools (why?)
Parcel of air sinks, it compresses and warms (why?).
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10. Summary Energy: fuel for the atmosphere
Heat: energy transferred from one object to another due to the temp difference between them: convection (important), and radiation (important) conduction (less important)
Rate of transfer depends on temperature difference
Other processes involved in heating/cooling air:
compression/expansion (important)
water phase change (important)
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11. Radiation – A Closer Look
sun’s energy transfer; radiation though electromagnetic (EM) waves of various wavelengths
wavelengths measured in microns (m):
1/1000 th of a millimeter
radiation from sun, 90% wavelengths are < 1.5 m
sun’s radiation wavelength spectrum:
UV: UltraViolet < 0.4 m
Visible ( m) what we can see (most radiation from the sun is within this range)
IR: InfraRed > 0.7 m
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12. Radiation: wavelength and energy (Figure 2.8)
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13. Wien’s Law: max = constant / T
Radiation: Three Laws
Anything with temperature (T > 0 K) emits radiation (E) in the form of electromagnetic waves.
The greater the temperature of an object, the shorter the wavelengths, , emitted. Also the peak emission of radiation shifts toward shorter wavelengths
Wien’s Law: max = constant / T
where max is the wavelength which maximum radiation occurs
The greater the temperature of an object, the more energy is radiated (over a given surface area) per second.
Stefan Bolzmann Law: E =  T4
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14. Sun’s Electromagnetic Spectrum (Figure 2.9)
Sun and Earth Radiation Spectrum (Figure 2.10) “Shortwave” Radiant energy from the Sun. “Longwave” Radiant energy from the Earth (IR part of the spectrum)
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15. What Happens to the Incoming (Shortwave) Radiation?
Absorbed: (ground, clouds, atmosphere: warms)
Scattered (Diffuse): all directions (clouds, atmosphere)
Reflected: back to where it came from (clouds, ground, atmosphere)
Albedo: reflectivity of surface for short wave radiation (mirror 100%, snow 75-80%, thick clouds 60-90%) depends on sun angle and surface (see Table 2-2 in Text)
Transmitted (Direct): passes through
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16. Summary
Radiation in the form of waves of different wavelengths (radiation spectrum)
Anything with temperature emits radiation
The higher the temperature:
the more energy radiated
the shorter the wavelengths
Radiation from sun: shortwave (most energy < 0.7 m: UV and visible)
Radiation from earth: longwave (IR)
Incoming radiation can be absorbed, scattered, reflected (albedo) and transmitted
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17. Emission, Absorption and Equillibrium Temperature
Object radiates more energy than it absorbs: cools
Object absorbs more energy than it radiates: warms
Object radiates = absorbs: temp constant (radiative equillibrium)
why doesn’t earth continue to warm?
Blackbody: absorbs all incoming radiation and emits max radiation possible for its temperature
Assume Earth a blackbody: equillibrium temp (solar radiation absorbed = radiated IR or “emitted”) = -18 C
actual earth ave temp = 15 C (why?)
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18. The Atmosphere: a Selective Absorber of Radiation
Atmosphere (mix of gases): each gas is selective in the wavelengths of radiation it absorbs:
water vapor and CO2
do not absorb incoming shortwave (both UV and visible)
absorb most outgoing longwave (IR) O3
absorbs most incoming UV (but not visible)
does not absorb much outgoing longwave (IR)
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19. The Atmosphere: A Selective Absorber of Radiation
Most incoming radiation (visible and a portion of UV) reaches the surface and is absorbed (warms surface)
Earth emits IR which is absorbed by the atmosphere except for wavelengths between 8 – 11 m
IR in this wavelength band escapes into space: “Atmospheric Window”
absorbed IR by the atmosphere results in warming of atmosphere
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20. Radiation Absorption by Gases (Figure 2
Radiation Absorption by Gases (Figure 2.11) shaded area is the % of radiation at a particular wavelength absorbed by the gas
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21. Radiative Properties of Clouds
Clouds (tiny liquid droplets) – especially low thick ones:
reflect incoming shortwave,
good absorber of IR (even absorb IR between 8 – 11 m, clouds close the Atmospheric Window)
good emitters of IR upward from top and downward to earth from bottom.
During daytime, why are cloudy days cooler?
During night (esp during winter), why are cloudy, calm nights warmer than clear nights?
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22. Atmospheric Greenhouse Effect – Natural and Enhanced
water vapour, CO2 (and other trace gases) absorb much of the outgoing IR: atmosphere warms:
warm atmosphere radiates energy (IR) back to the earth, which is absorbed: surface warms
if no absorption of outgoing IR by these gases, the temp would -18 C (vs current ave temp 15 C the Natural Greenhouse Effect )
Enhancement of the Greenhouse Effect: more Greenhouse Gases (water vapor, CO2, methane, nitrous oxide, CFC’s) → more absorption of outgoing IR (warmer atmosphere), and more IR radiated to the earth and absorbed (warmer surface).
More GHG’s?: warmer atmosphere and surface
See
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23. Figure 2.12 Atmosphere without and with Greenhouse Effect
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24. Global Climate Change: Feedback Loops
Positive Feedback: reinforce effects of initial signal
Example: GHG , T , evap , water vapor , water vapor absorbs IR, T of atmos/earth , evap  and so on.
Negative Feedback: suppress effects of initial signal
Example: GHG , T , evap , water vapor , clouds , more incoming solar radiation reflected back into space, T , evap , water vapor , T of atmos/earth 
Positive and Negative Feedback loops on going, simultaneously
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25. Warming the Lower Atmosphere Air from Below (Fig 2.13)
Figure How is the Incoming Energy Partitioned
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26. Figure 2.17 How is the Incoming Energy Partitioned?
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27. FIGURE 2. 18 The earth-atmosphere energy balance
FIGURE 2.18 The earth-atmosphere energy balance. Numbers represent approximations based on surface observations and satellite data. While the actual value of each process may vary by several percent, it is the relative size of the numbers that is important.
Figure 2.18: The earth-atmosphere energy balance. Numbers represent approximations based on surface observations and satellite data. While the actual value of each process may vary by several percent, it is the relative size of the numbers that is important.

28. Summary
Incoming shortwave radiation: reflected, absorbed, scattered (diffuse), transmitted (direct).
Atmosphere is transparent to most incoming shortwave – reaches the surface
CO2 and water vapor:
ignore incoming but selectively absorb IR emitted by the earth
emit IR back to earth
this keeps the earth/atmosphere temp warm
increasing GHG’s enhance the greenhouse effect: net effect due to a series of + and - feedback loops.
Temperature of air and earth a result of a delicate balance of energy partitioning
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29. Daily Temperature Variation: Near Surface (Text Pg 56 –62)
Atmosphere is not a blackbody: absorbs some wavelengths of radiation and is transparent to others (“selective absorber”)
Earth is lie a blackbody: much better absorber and emitter of radiation than atmosphere
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30. Daily Temperature Variation: Near Surface
Day Time
Earth (blackbody):
absorbs all incoming wavelengths (except that which is reflected)
vs. atmosphere absorbs only part of UV
surface much warmer than air above.
air temp drops rapidly with height within a few meters of the surface.
Clouds:
reflect incoming (shortwave) back to space, daytime surface temps lower with clouds
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31. Daily Temperature Variation: Near Surface
Night
Earth (blackbody):
emits IR efficiently vs. air (not efficient IR emitter)
surface cools more rapidly than air above under clear skies
inversion – warm air over cold (air temp increases with height above ground)
“radiation inversions” : clear, calm nights
Low Clouds:
absorb outgoing IR, emit IR back to earth
night time surface temps greater (compared to clear nights)
no radiation inversion
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32. Figure 3.3 Air Temperature Changes with Height Near Surface:
Clear Night (Radiation Temperature Inversion)
Figure 3.2 Daily Temperature Variation
Figure 3.3: On a clear, calm night, the air near the surface can be much colder than the air above. The increase in air temperature with increasing height above the surface is called a radiation temperature inversion.
Stepped Art
Fig. 3-3, p. 62

33. Surface Temperature – Daily (Diurnal) Variation
Max surface temp mid to late p.m.
incoming shortwave radiation max at noon, then falls with lower sun angle but still exceeds outgoing IR radiation
Temp still increases
Temp drops when outgoing exceeds incoming
Min surface temp just after sunrise
outgoing radiation all night (no incoming), Temp drops until just after sunrise when incoming exceeds outgoing
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