Earth Sci chap 11
Ch 11 – Heating the Atmosphere
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I.
Weather influence all our lives
What country has greatest variety of wthr on earth?
We also influence wthr, through air pollution for example
wthr and climate
 definitions weather – state of atmosphere at partic place at partic time
 climate – a long-term composite or average of weather over a
long time
elements or properties that are measured and used to describe wthr
and climate:
- air temp
- humidity
- cloud conds
- type & amt of precip
- air pressure
- wind conds
…..elements inter-related
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II composition of atmosphere
air defined – a mixture of many discrete gases, tiny solids and liquid
particles too
air makeup generally similar up to height of 50 miles
when clean, dry, air made up primarily of 2 gases, ____ and _____
these gases important in support of life, but play minor role in wthr
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variable amts of other components ARE important in affecting
wthr/climate
1. water vapor - % varies from 0 to 4 by volume
why is water vapor important?
Source of clouds and precip
Absorbs heat from earth and sun
Released or absorbed heat known as latent (“hidden”) heat
Earth sci wk 11 p.2
Water vapor helps transport latent heat from one region to another,
and can be source of energy for storms
2. Dust – includes both visible dirt and microscopic particles, both
organic and inorganic
Particles act as nuclei for condensation (clouds, fog)
Can also act to reduce incoming solar radiation
Dust causes red and orange colors of sunrise – sunset
3. Ozone (O3) – usu found in stratosphere, above 6 miles up, but
not much in atmosphere
Ozone very important because it absorbs UV radiation from sun
W/out ozone, too much UV would make it to the surf of Earth
But we do have a problem currently…..
Ozone depletion occurring (Fig 11.3) over last 20 yrs, espec over
poles
CFCs have been the main problem (cholorfluorocarbons), thrown
into atmosphere over last 50 yrs…sources include coolants,
solvents, aerosol propellents (like Right Guard??), and styrofoam
cup/home insulation manufacture
Sunlight breaks CFCs up…. Cl in the CFCs then breaks up the
ozone
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Most serious threat to man in incr risk of skin cancer.
International agreement has been developed to reduce CFC production,
and we hope that ozone layer will recover and return to more healthy
state by middle of 21st century
III.
Structure / height of atmosphere
How high does the atmosphere extend? No sharp boundary, but top is
assoc with end of gas molecules..above this is the vacuum of outer
space
Look at changes in properties to help define the top..
Earth Sci wk 11 p.3
A. Pressure (due to weight of air) changes Fig 11.4
– start at 1 bar = 14.7 psi at sea level
– pressure decreases exponentially – by altitude of 3.5 mi (about
18,000 ft), pressure half of that at sea level
– by 10 miles up, 90% of atmosphere traversed
B. Temperature changes - 4 subdivision of atmosphere— Fig 11.6
Thermosphere
Mesosphere
Stratosphere
Troposphere
above 50 miles
30 up to 50 miles
18 up to 30 miles
0 to 18 miles
Tropo – temp decreases from bottom to top (- 70oF at the tropopause)
Strato – temp incr from bottom (-70 F) to top (32 F at the stratopause)
Temp increases because ozone absorbs heat, thus strato is
warmed
Meso – temp decr from bottom (32 F) to top (-130 F at the mesopause)
Thermo - temp incr from bottom (-130 F) to top (-60 F)
IV. Earth-Sun Relationships
energy comes from where??
solar energy not distrib equally….unequal heating causes imbalances
driving ocean currents, winds,etc because of drive toward equilibrium
If sun turns off, currents will turn off
look at some key elemts…
 rotation and revolution … which is which???
and what is the “circle of illumination”?
 Seasons –
why colder in winter than summer?
- yes, length of day is shorter
- but key is the sun angle
Earth Sci wk 11 p.4
more perpendicular the sun is to surface of Earth, the more energy is
concentrated in a given area
also, the more perpendicular the sun to surface, the less atmosphere
the rays must penetrate (so they get less filtered by the atmos)
example in Fig 11.8 , 11.9
equatorial vs mid-latitude vs polar regions
so the diff in atmos thickness is why we enjoy watching sunrise or
sunset, but get blinded by sunlight if we look directly overhead at noon
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causes of the seasons
earth orientation (tilted axis) is the key…causes variations in sun angle
and length of daylight
if axis were not tilted (just vertical), it would always be incredibly hot at
equator and incredibly cold at poles, because sun would always beat
down directly on Equator and just “scrape” the poles
instead, positions of continents and oceans CHANGE relative to sun
throughout the year as earth circles the sun Fig 11.10
note variance in “leaning” either toward or away from sun of 23 ½
this causes sun angles to vary widely at places north of Tropic of
Cancer or south of Tropic of Capricorn
o
example here in NYC – sun as high as 73 ½ o above horizon in
summer, as low as 26 ½ o above it in the winter
 solstices & equinoxes…… what’s what??
4 days define these terms… Fig 11.10
on June 21 or 22, Northern hemi is leaning most toward sun, and
sun’s rays strike DIRECTLY (perpendicular) on line known as Tropic of
Cancer (23 ½ o N latitude)
this is first day of summer & longest day of year in N Hemi, and also
the summer solstice for the N hemi
Earth Sci wk 11 p. 5
on Dec 21 or 22, the South hemi leaning most toward sun, and sun’s
rays strike DIRECTLY (perpendicular) on line known as Tropic of
Capricorn (23 ½ o S latitude)…this is the winter solstice & shortest day
of year for the N. hemi, but what would it be for the southern hemi???
likewise, first day of Spring in N hemi, Mar 21 is the spring equinox
and first day of Fall in N hemi, Sept 21, is the autumn equinox
on both these days, suns rays strike Equator perpendicularly … Fig
11.10
aside here …”equinox” means “equal_____?”
interesting contrast in amount of daylight…NYC again..
….. 15 hrs of daylight on June 21, only 9 hrs of daylight on Dec 21
Fig 11.11 shows this well..compare the circle of illumination with the
latitude of NYC for each of the 4 days….espec note this by looking
down on the N. pole on RH side of Fig
V. Mechanisms of heat transfer
definition ; temperature is the measure pof the “average motion
of molecules” heat always moves from hot to cold (fast motion to
slower motion), just like your car if take your foot of the gas…
3 types of heat transfer mechs exist: Fig 11.12
1. conduction
2. convection
3. radiation
conduction – transfer of heat through matter by molecular activity (like
heat through a spoon)…not too important as far as earth goes
convection – transfer of heat by movement of mass from one place to
another (eg, convection current in the mantle of Earth.. or hot currents
of water in pan flow to colder areas of pan)
Radiation is the ONLY mechanism that can transfer heat through a
vacuum (this kept people from believing in kinetic theory of heat for
many years…they couldn’t envision how heat could be molecular if
there are no molecules in a vacuum, yet heat could be transmitted
ACROSS a vacuum)
19th cen scientists used “ether” as the medium to transfer heat from Sun
to Earth, because of difficulty in visualizing how else to get the heat
across vacuum….
Earth Sci wk 11 p.6
So vast majority of energy that comes to Earth from sun is by
mechanism of radiation
(Fig 11.13) heat is part of the electromagnetic spectrum of energy that
contains light, microwaves, infrared heat, x rays, gamma rays, radio/TV
waves
all radiation moves through vacuum at the speed of light
analogy to ocean waves in the transmission of energy, including diff
wavelengths of ocean waves corresponding to diff energy levels of E-M
spectrum
note the visible light spectrum (white light) is actually broken up into a
number of diff wavelengths of diff colors…ROYGBV (“Roy G. Biv”)
which are the longest light wavelengths? shortest? good test
questions…
some basic radiation laws:
1. all objects emit radiant energy
2. hotter objects radiate more energy per unit area than colder
objects
3. the hotter the radiator, the shorter the wavelength
sun short-wave vs earth longer-wave for instance
4. objects that are good absorbers are also good emitters (eg,
“blackbody radiators”)
but gases are selective in absorbance and radiance..
so atmosphere abosrbs some wavelengths, but lets others right through
(ocean does this too..absorbs ROY, transmits GBV)
visible light readily travels through atmos, but longer wavelengths
emitted by Earth have trouble escaping (part of problem w/ greenhouse
gases and global warming is that infrared heat has trouble getting back
out into space, and warms Earth..)
VI. Paths taken by Incoming solar radiation
only 25% of sun energy actually penetrates directly to earth surf…rest is
absorbed, scattered, or reflected back into space..what controls this is
the wavelength of the energy…
Earth Sci wk11 p.7
gases & dust scatter the incoming energy , about 30% goes back into
space, so earth’s total albedo (fraction of total incoming energy that is
reflected) is about 30%
albedo can change dramatically depending on cloud cover, sun angle,
etc
lower sun angle, higher cloud cover all cause higher reflectance, higher
albedo
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absorption of incoming energy
for UV energy from sun….
- N is a poor absorber
- O2 and O3 good absorbers of UV radiation (causing high T in
stratosphere)
- water vapor a good absorber too, along w/ O2 and O3
for visible radiation from sun…
- no gases are good absorbers , so most visible radiation
reaches the Earth surface (atmosphere “transparent” to incoming solar
radiation)
VII. Heating the Atmosphere – Greenhouse Effect
 about 50% of solar energy that hits the top of atmos makes it down
to Earth surface
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most of this 50% then reradiated back out, but at lower energy levels
and Longer Wavelengths Fig 11.16
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Problem- atmosphere is a good absorber of the longer wavelengths,
espec CO2 and water vapor, so where these are concentrated, in
lower troposphere, near to earth surf, is where warming of
atmosphere occurs….
- heating tends to occur from “ground up”
- so the further away from “radiator” (earth surface) you go, the
colder it gets
- also, earth surface continually supplied by incoming solar radiation
as well as re-radiated heat coming from gases that initially absorbed
the heat
Earth Sci wk 11p.8
this is known as the “greenhouse effect”, because of analogy to a
greenhouse.
- glass allows short-wave radiation, like UV & visible in, then
objects inside become heated
- objects re-radiate the heat, but at longer wavelengths, and
glass won’t let long-wave out
so greenhouse gets heated up
VIII. Global Warming – Fig 11.17
scientists (at least some) believe that combustion of fossil fuels has
greatly increased the CO2 levels of atmosphere since the early
1800s
some projections suggest that CO2 conentration could increase by
50% or more in next century, which could produce an incr of 1.5 –
4.5 deg C (3-9 deg F) in avg global temp
this would equal the warming that has occurred since the last Ice
Age, but more rapidly.
there ARE some possible consequences:
1. shifts in temp & rainfall patterns
2. sea level rise & shoreline recession of major proportions
3. change in storm tracks, more hurricanes
4. incr in heat waves and droughts
IX. Temp Msrmt and Data collected
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daily mean = (max + min)/2
daily range = (max-min)
monthly mean
annual mean = (sum of monthly means)/12
annual range = max monthly mean – min monthly mean
Earth Sci wk 11 p.9
X. controls on temperature
control defined as any factor causing temp to change
- biggest factor = diffs in amt of incoming solar radiation, due to diffs
in :
1. sun angle
2. length of daylight
both these are a function of latitude
but others include:
- differential heating of land , water
- altitude
- geographic position
- ocean currents
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land vs water…land heats more rapidly, to higher temp
land cools more quickly, to lower temp
so water has moderating influence because of factors such as :
- specific heat of water very high (absorbs a lot w/out incr in T)
- heat penetrates to depth in ocean (spreads out)
- water can mix heated mass with cooler mass, dissipating heat
- evaporation pulls lot of energy out of the water
Vancouver, BC vs Winnipeg, Manitoba Fig 11.19
picture says a thousand words…..which is more “moderate”, less
extreme?
can even see the diffs in hemispheres (table 11.3) – which is more
moderate? which has more water?
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altitude – elev above sea level translates to feeling like a higher
latitude, because it’s colder there than at sea level
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geographic position – NYC vs Eureka, CA as examples
- annual temp range much higher in NYC --- why? (hint : wind &
weather patterns coming from where? )
Earth Sci wk 11 p.10
XI. World Distrib of Temp
look at map with “isotherms” – lines of “equal temp” Figs 11.20 & 21
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what do you see?
- warmest and coldest temps are over land in either month
- very coldest temps in Jan are found nr North Pole,
while very coldest temps in July are found nr South Pole..
what does this reflect to you ?? what does this tell you about
earth axis?
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what else?
- ocean currents deflect the isotherms..cold currents bend isotherms
toward the equator, indicating cooler water closer to equator than
you’d expect…likewise, warm currents bend the isotherms out
toward the poles, spreading the warm water further poleward than
you’d expect..
what else?
- annual temp ranges (jan vs july) are greatest at where?…poles
or equator