http://www.washingtonpost.com/blogs/capital-weather-gang/
By Jason Samenow (Posted at 12:31 PM ET, 01/13/2012)
Lightning deaths by year (19402011) and tornado deaths by
year (1950-2011) (Data from
National Weather Service)
Tornado deaths per million
people in United States since
late 1800s (NOAA)
Q: The peak in 2011 was due to a) Poor forecasting; b) lack of
warning or education of public; c) simply too many and
1
too strong tornadoes.
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
1 degree latitude = 111 km = 60 nautical miles
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
1 ft2 = 0.32 m2 = 0.09 m2
(c) Volume: m3
1 liter (l) = 1000 cm3 = 0.264 gallon (gal) US
(d) Mass: kg
1 kg = 2.2 lb
So 20 mi/gal = 20*1.6 km/(1/0.26) l ~ 8 km/l
Q: where is the gas price higher? a) in the U.S. ($4/gal);
b) in China ($1.5/liter); c) same
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
earth’s 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
(i) Power of 10
10-9 10-6 10-3 10-2 102
103
106 109 1012 1015
Q: The work from lifting weight of 50 kg for 30 cm is
a) 1.5 J; b) 15 J; c) 150 J; d) 1500 J
5
(j) Pressure: pascal (Pa) = N/m2
P = F/Area
1 Pa = 1 N/m2
1 millibar (mb) = 100 Pa = 1 hecto Pa = 1 hPa
sea level surface pressure = 1013 mb
1 mb ~ 10 m in depth
Q: what is the typical height of 850 mb above
sea level? a) 1.5 km; b) 2 km; c) 8.5 km
6
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 = 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. 457 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
Why the earth has seasons
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: used in most countries
Fahrenheit scale: used for surface air T in U.S.
temperature conversions
• Every temperature scale has two physically-meaningful
characteristics: a zero point and a degree interval.
Q: A hot iron has lots of: a) energy; b) heat,
while touching it will transfer heat to hand.
11
Q: At the top of
Mt. Everest, will
the boiling point
temperature
a) increase;
b) decrease;
c) not change?
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
at boiling point temperature, molecules anywhere in the liquid
could escape and vapor pressure equals the environmental
pressure

sensible heat: we can feel and measure with a thermometer
Q: Cloud formation [a) warms; b) cools; c) does not change the
temperature of] the atmosphere?
Q: Why is perspiration an effective way to cool your body?
13
Stepped Art
14
Conduction
Conduction: heat transfer
within a substance by
molecule-to-molecule
contact due to T difference
good conductors: metals
poor conductors: air
For instance, touching a hot
ground in summer in Tucson
might burn your finger, but your finger is fine at 1 cm above surface.
Q: Touching metal and wood in room T with your hand, which one
15
do you feel cooler: a) metal; b) wood; c) equal
Convection

Convection:

Thermals: rising bubbles
heat transfer
by mass movement of a
fluid (such as water and air)
of air that carry heat upward by
convection
• Soaring birds, like hawks and
falcons, are highly skilled 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: 3*105 km/s


Wein’s law
wavelength at maximum radiation: λmax = 2897 (μmK)/T
Stefan-Boltzmann law
Radiative energy flux (Wm-2) : E = σT4
Q: In a vacuum, there is still: a) conduction only; b)
convection only; c) radiation only; d) all of them?
Q: Heat is transferred in a metal by: a) conduction only; b)
convection only; c) both
17
•All things emit radiation
•Higher T leads to shorter 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)
sunburn/skin cancer
•UV-A (.32-.4 μm)
tan, skin cancer
•Most sunscreen
reduces UV-B only
18
Radiation


vertical scale
differs much
electromagnetic
spectrum
ultraviolet radiation
(UV-A, B, C)

visible radiation (0.4-0.7
μm)
shortwave (solar) radiation

infrared radiation
longwave (terrestrial)
radiation
19
Q: I can see you, because: a) you emit visible light;
b) you reflect visible light
20
Selective Absorbers
Atmospheric window: 8-12 μm
The best greenhouse gas in the
atmosphere is water vapor,
followed by CO2
Atmospheric absorption of solar radiation is
small
Atmospheric absorption of infrared radiation
is large
21
In general, earth’s surface absorbs almost all infrared radiation.
If all radiation is absorbed by an object, this object is called
“blackbody” and earth’s surface is nearly a blackbody.
Q: does a blackbody need a black color? a) yes, b) no
Low-level clouds are also good absorbers of longwave radiation
(and hence increase surface air temperature at night)
Q: Why do high-level clouds not significantly increase
surface air temperature at night?
Q: does ozone strongly affects radiation (see previous two
slides)? Answer: No. It absorbs UV below 0.3 μm (which
contains small amount of solar radiation only). It also
absorbs infrared radiation around 9.6 μm only.
Q: Does ozone hole affect climate change? a) yes; b) no.
22
Balancing Act - Absorption, Emission,
and Equilibrium
1. Without atmospheric green house gases (but with clouds), the
earth average temperature is -18oC due to the balance of solar
heating and longwave radiation loss
2. With atmosphere, the earth surface temperature is 15oC due
to the selective absorption of the atmosphere
3. In other words, the 33oC difference is caused by the
atmospheric green house effect.
This statement
in the book is
incorrect!
23
Zeng (2010; Eos Trans.)
Without atmosphere (i.e., no greenhouse gases, no clouds,
no aerosols), the earth average temperature is -5oC 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 15oC
due to the selective absorption of the atmosphere
Therefore, the atmosphere effect refers to the 20oC
difference (rather than 33oC)
24
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 to
melting 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
25
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) 2 km; c) 4
km
26
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
27
Scattered and Reflected Light

Scattering: blue sky, white sun, and red sun

Reflection: more light is sent backwards

Albedo: ratio of reflected over incoming solar radiation
fresh snow: 0.8
clouds:
0.6
desert:
0.3
grass:
0.2
forest:
0.15
water:
0.1
Surface absorption of solar
radiation is simply (1 – albedo).
Surface is a very good absorber
of infrared radiation (~0.95)
Snow is a very good absorber of
infrared radiation, but it is a poor
absorber of solar radiation.
28
The Earth’s Annual Energy Balance
Q: What happens to the solar energy at top of the earth’s
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)
29
Solar constant = 1367 W/m2
30
31
Heat is transferred by both atmosphere and ocean
Q: What is the fundamental driving force of wind patterns in
the atmosphere? A: differential heating
32
Why the Earth has Seasons
Q: the earth’s season is caused by: a) tilt of the earth’s axis; b)
earth-sun distance variation
Q: the earth-sun distance is longer in: a) winter; (b) summer; c)
equal
Q: if the earth’s axis
were NOT tilted,
would we still
have seasons?
a) yes; b) no
Q: will sun set at 70oN
on June 21?
a) yes; b) no
33
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
34
While the astronomic
winter starts on
December 21,
meteorological winter
season is usually
defined as DJF (DecJan-Feb) based on the
3 coldest months
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)
35
Computing the maximum solar angle at noon on 21 June at latitude
is simply: (90 +23.5 – latitude)
Q: In Tucson summer, the sun rises from:
a) northeast; b) nearly east; c) southeast
Stepped Art
36
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
37
Q: why is the
bridge in this
figure the first to
become icy?
38