Transcript Document

Appendix A
(a) Length: m
1 km = 1000 m;
1 m = 100 cm = 1000 mm = 106 micrometer (μm)
1 inch (in.) = 2.54 cm
1 foot (ft) = 12 in. = 12*2.54 = 30.48 cm = 0.3048 m
1 mile (mi) = 1.61 km
1 nautical mile = 1.15 mi = 1.85 km
(b) Area: m2
1 mi2 = 1.612 km2 = 2.59 km2
(c) Volume: m3
1 liter (l) = 1000 cm3 = 0.264 gallon (gal) US
(d) Mass: kg
1 kg = 2.2 lb
(e) Speed: m/s
1 km/hr = 1000m/3600s = 0.28 m/s
1 mi/hr = 1609m/3600s = 0.45 m/s
1 knot = 1 nautical mile/hr = 1850m/3600s = 0.51m/s
(f) Force: newton (N) = kg m/s2
F = ma
`a’ is acceleration (or change of speed
with time)
1 dyne = 1 g cm/s2 =10-3 kg 10-2 m/s2 = 10-5 N
(g) Energy: joule (J) = Nm
E = FL
`L’ is distance
1 J = 1 Nm = 0.24 Calorie (cal)
(h) Power: watt (W) = J/s
P = change of energy with time
1 horse power (hp) = 746 W
(i) Power of 10
10-9 10-6
10-3 10-2
102
103
106 109
(j) Pressure: pascal (Pa) = N/m2
P = F/Area
1 Pa = 1 N/m2 = 1 (kg m/s2)/m2 = 1 kg s-2 m-1
1 millibar (mb) = 100 Pa = 1 hecto Pa = 1 hPa
sea level surface pressure = 1013 mb
1 millimeter of mercury (mm Hg) = 1.33 mb
because
Hg density = 13,546 kg/m3;
earth’s gravity = 9.8 m/s2;
Over unit area (m2),
1 mm Hg mass = 10-3 * 13,546
= 13.5 kg
F = mg = 13.5 *9.8 N = 133 N
P = F over unit area = 133 Pa = 1.33 mb
(k) Temperature: kelvin (K)
K = oC + 273;
oC = 5/9 (oF -32)
oF = 9/5 oC + 32
For instance
104 oF = 40 oC
20oC = 68 oF
(Table A.1 on p. 437 could also be used)
Q: if temperature changes by 1 K, how much does
it change in oC and oF? (A: 1 oC; 1.8oF)
Chapter 2: Warming
the Earth and the
Atmosphere



Temperature and heat transfer
Balancing act - absorption,
emission and equilibrium
Incoming solar energy
Temperature and Heat
Transfer
Air T is a measure
of the average
speed of the
Molecules
Warm
less dense
Temperature Scales





kinetic energy, temperature and heat
K.E. = mv2, Internal energy = CvT,
Heat = energy transfer by conduction,
convection,and radiation
Kelvin scale: SI unit
Celsius scale:
Fahrenheit scale: used for surface T in U.S.
temperature conversions
• Every temperature scale has two physically-meaningful
characteristics: a zero point and a degree interval.
Fig. 2-2, p. 27
Latent Heat - The Hidden
Warmth

phase changes and energy exchanges
evaporation: faster molecules escape to air; slower
molecules remain, leading to cooler water T
and reduced water energy; lost energy carried
away by (or stored in) water vapor molecules
Q: does the formation of clouds warm or cool the
air in the clouds?

sensible heat: we can feel and measure
• Latent heat explains why perspiration
is an effective way to cool your body.
Stepped Art
Fig. 2-3, p. 28
Conduction

Conduction:
heat transfer within a substance
by molecule-to-molecule contact
due to T difference

good conductors:
metals

poor conductors:
air (hot ground only
warms air within
a few cm)
Convection

Convection:

Thermals
heat transfer
by mass movement of a
fluid (such as water and air)
• Soaring birds, like hawks
and falcons, are highly
skilled at finding thermals.
• Convection (vertical) vs
Advection (horizontal)
• Rising air expands and cools while
sinking air warms by compression
Radiation

Radiation: energy transfer between objects by electromagnetic
waves (without the space between them being necessarily heated);
packets of photons (particles) make up waves and groups of waves
make up a beam of radiation;

electromagnetic waves
Q: are molecules needed?
In a vacuum, speed of light: 3*105 km/s

Wein’s law
λmax = 2897 (μmK)/T

Stefan-Boltzmann law
E = σT4
•All things emit radiation
•Higher T leads to shorted λ
•Higher T leads to higher E
•Shorter λ photon carries more energy
•UV-C (.2-.29 μm)
ozone absorption
•UV-B (.29-.32 μm)
runburn/skin cancer
•UV-A (.32-.4 μm)
tan, skin cancer
•Most sunscreen
reduces UV-B only
Fig. 2-7, p. 32
Radiation


electromagnetic
spectrum
ultraviolet radiation
(UV-A, B, C)

visible radiation (0.4-0.7
μm)
shortwave (solar) radiation

infrared radiation
longwave (terrestrial)
radiation
Fig. 2-8, p. 34
Balancing Act Absorption,
Emission, and
Equilibrium
Selective Absorbers and the
Atmospheric Greenhouse
Effect
 blackbody radiation
perfect absorber; don’t have
to be colored black;
radiative equilibrium T = 255K;
actual T = 288K

selective absorbers
snow: good absorber of infrared
radiation, but not solar radiation

atmospheric greenhouse effect
• The best greenhouse gas is water
vapor, followed by CO2
Enhancement of the
Greenhouse Effect

global warming: due to increase of CO2, CH4, and
other greenhouse gases;
global average T increased by 0.6 C in the past 100 yr;
expected to increase by 2-6 C at the end of 21st century

positive and negative feedbacks
• Positive feedback: increasing temperatures lead to
melting of Arctic sea ice, which decreases the albedo.
• Positive water vapor-temperature feedback
• Potentially negative cloud-temperature feedback
Warming the Air from Below
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

radiation
conduction
convection
• Fog “burns off” from the bottom up.
Incoming Solar
Energy
Scattered and Reflected Light
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Scattering: blue sky, white sun, and red sun
Reflection: more light is sent backwards
Albedo:
ratio of reflected
over incoming
radiation;
fresh snow: 0.8
clouds:
0.6
desert:
0.3
grass:
0.2
forest:
0.15
water:
0.1
The Earth’s Annual Energy
Balance


What happens to the solar energy that
reaches the top of the earth’s
atmosphere?
What happens to the solar energy that is
absorbed by the earth’s surface and by the
atmosphere?
Solar constant = 1367 W/m2
Fig. 2-15, p. 41
Fig. 2-16, p. 42
Fig. 2-17, p. 43
Why the Earth has Seasons


earth-sun distance: closer in winter
tilt of the earth’s axis
• Earth-sun
distance has
little effect on
atmospheric
temperature.
Seasons in the Northern
Hemisphere



insolation
summer solstice
spring and autumn equinox
Seasons in the Southern
Hemisphere



tilt
solstice
equinox
December 21 is the 1st day of
winter in astronomical definition
not in meteorological definition
Stepped Art
Fig. 2-24, p. 50
Local Seasonal Variations


slope of hillsides: south-facing hills warmer & drier
vegetation differences
• Homes can exploit
seasonal variations:
large windows
should face south.