Appendix A

1
Appendix 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. 122.54 30.48 cm
  0.3048 m
• 1 mile (mi) 1.61 km
• 1 nautical mile 1.15 mi 1.85 km
• Q 10 µm ? a) 10-5 m b) 10-6 m c) 10-7 m

2

• (b) Area m2
• 1 mi2 1.612 km2 2.59 km2
• Volume m3
• 1 liter (l) 1000 cm3 0.264 gallon (gal)
  US
• (d) Mass kg
• 1 kg 2.2 lb
• So 20 mi/gal 201.6 km/(1/0.26) l 8 km/l

3
(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
earths gravity g 9.8 m/s2
4

• (g) Energy (heat, work) joule (J) Nm
• E FL L is distance
• 1 J 1 Nm 0.24 Calorie (cal)
• 1 cal heat needed to raise temperature from
  14.5oC
• to 15.5oC of 1 cm3 of water
• (h) Power watt (W) J/s
• P change of energy with time
• 1 horse power (hp) 746 W
• Power of 10
• 10-9 10-6 10-3 10-2 102
  103 106 109
• Q The work from lifting weight of 50 kg for 0.3
  m is
• a) 1.5 J b) 15 J c) 150 J d) 1500 J

5

• 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

6
1 millimeter of mercury (mm Hg) 1.33 mb
because Hg density 13,546 kg/m3
earths 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 Q surface
pressure 1013 mb ? a) 500 mmHg b) 760
mmHg c) 1000 mmHg
7
(k) Temperature kelvin (K) K oC 273
oC 5/9 (oF -32) oF 9/5
oC 32 (Table A.1 on p. 437 could also be
used) Q 104 oF ? a) 20 oC b) 30 oC
c) 40 oC Q if temperature changes by 1
oC, how much does it change in oF?
a) 5/9 oF b) 1 oF c) 1.8oF
8
Chapter 2 Warming the Earth and the Atmosphere

• Temperature and heat transfer
• Balancing act - absorption, emission and
  equilibrium
• Incoming solar energy

9
Temperature and Heat Transfer
Air T is a measure of the average speed of the
Molecules
Warm

less dense
10
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-meaningfulcharacteristics a zero
  point and a degree interval.

11

Fig. 2-2, p. 27
12
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 molecule
• sensible heat we can feel and measure
• Q Cloud formation a) warms b) cools
  c) does not change the
• temperature of the atmosphere?

• Latent heat explains why perspirationis an
  effective way to cool your body.

13

Stepped Art
Fig. 2-3, p. 28
14
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)

15
Convection

• Convection heat transfer by mass movement of a
• fluid (such as water and air)
• Thermals

• Soaring birds, like hawks
• and falcons, are highlyskilled at finding
  thermals.
• Convection (vertical) vs
• Advection (horizontal)
• Q why does the rising air expands
• and cools?

16
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
• In a vacuum, speed of light 3105 km/s
• Weins law
• ?max 2897 (µmK)/T
• Stefan-Boltzmann law
• E sT4

Q In a vacuum, there is still a) Conduction
only b) convection only c) radiation only d)
all of them
17

• All things emit radiation
• Higher T leads to shorter ?
• Higher T leads to higher E
• Shorter ? photon carries more energy
• UV-C (.2-.29 µm)
• ozone absorption
• UV-B (.29-.32 µm)
• sunburn/skin cancer
• UV-A (.32-.4 µm)
• tan, skin cancer
• Most sunscreen
• reduces UV-B only

Fig. 2-7, p. 32
18
Radiation

• electromagnetic spectrum
• ultraviolet radiation (UV-A, B, C)
• visible radiation (0.4-0.7 µm)
• shortwave (solar) radiation
• infrared radiation
• longwave (terrestrial)
• radiation

19

Fig. 2-8, p. 34
20
Balancing Act - Absorption, Emission, and
Equilibrium
Without atmosphere, the earth average temperature
is -18 oC due to the balance of solar heating of
half of the earth and longwave radiation loss
from the earth surface With atmosphere, the
earth surface temperature is 15 oC due to the
selective absorption of the atmosphere In other
words, the 33 oC difference is caused by the
atmospheric green house effect
21
Selective Absorbers

• in general, earths surface is nearly
• black for infrared radiation
• In particular, snow is good absorber of infrared
  radiation, but not solar radiation
• Atmospheric window 8-12 µm
• The best greenhouse gas in the
• atmosphere is water vapor,
• followed by CO2
• Low-level clouds are also good absorbers of
  longwave radiation (and hence increase air
  temperature at night)

22
Enhancement of the Greenhouse Effect

• global warming due to increase of CO2, CH4, and
  other greenhouse gases
• global average T increased by 0.6 oC in the
  past 100 yr
• expected to increase by 2-6 oC at the end of
  21st century
• positive and negative feedbacks

• Positive snow feedback a) increasing
  temperatures lead tomelting of snow/ice b)
  this decreases surface albedo and increases
  surface absorption of solar radiation c) this
  increases temperature
• Potentially negative cloud-temperature feedback

Q What is the water vapor-temperature
feedback? Answer 1) increasing air temperature
2) increasing evaporation 3)
increasing water vapor in the air 4) water vapor
is an atmospheric greenhouse gas
5) increasing air temperature 6) positive
feedback
23
Warming the Air from Below

• Radiation heat the ground
• Conduction transport heat upward within 1 few cm
  of ground
• Convection transport heat upward within 1 km of
  ground

Only under special conditions, can air moves
above 1 km height and form clouds. Q How high
can air parcel move up in Tucson in summer
afternoon in general? a) 1 km b) 3 km c) 5 km
24
Incoming Solar Energy
Light scattering light deflected in all
directions (forward, sideward, and backward),
called diffuse light, by air molecules and
aerosols. Q Why is the sky blue? Answer 1)
because air molecules are much smaller than the
wavelength of visible light, they are most
effective scatterers of the shorter (blue) than
the longer (red) wavelengths 2) diffuse light is
primarily blue Q why is the sun perceived as
white at noon? A because all wavelengths of
visible lights strike our eyes Q Why is the
sun red at sunset? A 1) atmosphere is thick 2)
shorter wavelengths are scattered and only red
light reaches our eyes

25
Scattered and Reflected Light

• 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

26
The Earths Annual Energy Balance

• Q What happens to the solar energy at top of the
  earths atmosphere, in the atmosphere, and at
  surface? A next slide

Q Most solar energy on average is a) absorbed
by surface b) absorbed by atmosphere c)
reflected and scattered to the space Q What is
the energy balance at top of the atmosphere, in
the atmosphere, and at surface? A see slide Q
top 100 (solar) 30 (reflection) 70
(longwave) surface 51 (solar) 7
(convection) 23 (evap) 21 (net longwave)
air 7 (conv) 23 (evap) 19 (solar) 49 (net
longwave)
27

Solar constant 1367 W/m2
Fig. 2-15, p. 41
28

Fig. 2-16, p. 42
29

Heat is transferred by both atmosphere and
ocean Q What is the fundamental driving force of
wind patterns in the atmosphere? A
differential heating
Fig. 2-17, p. 43
30
Why the Earth has Seasons

• earth-sun distance closer in winter
• tilt of the earths axis

• Earth-sun distance has little effect on
  atmospheric temperature.

• Q if the earths axis were NOT tilted, would we
  still have seasons?
• yes b) no
• Q will sun set at 70oN on June 21?
• a) yes b) no

31
Seasons in the Northern Hemisphere
Factors determining surface heating by solar
energy 1) solar angle 2) time length from
sunrise to sunset. Q why is Arizona warmer in
summer than northern Alaska where sun shines for
24 hours (see figure)? A sun angle is too low in
Alaska so that 1) solar insolation (i.e.,
incoming solar radiation) per unit area is too
small, and 2) atmospheric path for solar rays is
much longer and most of the solar energy is
scattered, reflected, or absorbed by the
atmosphere
32
Q Why is temperature higher at 40oN on June 21
than on Dec 21? a) longer daytime b) higher
solar angle c) both a) and b)
33

Q In Tucson summer, the sun rises from a)
northeast b) nearly east c) southeast
Stepped Art
Fig. 2-24, p. 50
34
Local Seasonal Variations

• slope of hillsides south-facing hills warmer
  drier
• vegetation differences

Q Without considering views, should Tucson homes
have large windows facing a) south b)
north? Q What would be the answer for a North
Dakota home? a) south b) north