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http://www.washingtonpost.com/blogs/capital-weather-gang/By Jason Samenow (Posted at 12:31 PM ET, 01/13/2012)

Lightning deaths by year (1940-2011) 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 too strong tornadoes.

Appendix AAppendix A(a) Length: m1 km = 1000 m; 1 m = 100 cm = 1000 mm = 106 micrometer (μm)

1 inch (in.) = 2.54 cm1 foot (ft) = 12 in. = 12*2.54 = 30.48 cm = 0.3048 m1 mile (mi) = 1.61 km1 nautical mile = 1.15 mi = 1.85 km1 degree latitude = 111 km = 60 nautical miles

Q: 10 μm = ? a) 10-5 m; b) 10-6 m; c) 10-7 m

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(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

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(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

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(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

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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

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Chapter 2: Chapter 2: Warming the Warming the Earth and the Earth and the AtmosphereAtmosphere Temperature and heat transferTemperature and heat transfer

Balancing act - absorption, Balancing act - absorption, emission and equilibriumemission and equilibrium

Why the earth has seasonsWhy the earth has seasons

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Temperature and Temperature and Heat TransferHeat Transfer

Air T is a measureof the averagespeed of the Molecules

Warm less dense

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Temperature ScalesTemperature Scales kinetic energy, temperature and heatkinetic energy, temperature and heat

K.E. = mvK.E. = mv22, Internal energy = C, Internal energy = CvvT, T,

Heat = energy transfer by conduction, Heat = energy transfer by conduction,

convection, and radiationconvection, and radiation Kelvin scale: SI unitKelvin scale: SI unit Celsius scale: used in most countriesCelsius scale: used in most countries Fahrenheit scale: used for surface air T in U.S.Fahrenheit scale: used for surface air T in U.S. temperature conversionstemperature conversions

• Every temperature scale has two physically-meaningfulEvery temperature scale has two physically-meaningfulcharacteristics: a zero point and a degree interval.characteristics: a zero point and a degree interval.

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Q: A hot iron has lots of: a) energy; b) heat, while touching it will transfer heat to hand.

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Q: At the top of Mt. Everest, will the boiling point temperature a)increase;b)decrease;c)not change?

Latent Heat - The Hidden Latent Heat - The Hidden WarmthWarmth phase changes and energy exchangesphase changes and energy exchanges

evaporation: faster molecules escape to air; slower evaporation: faster molecules escape to air; slower molecules remain, leading to cooler water Tmolecules remain, leading to cooler water T and reduced water energy; lost energy carriedand reduced water energy; lost energy carried away by (or stored in) water vapor moleculeaway by (or stored in) water vapor molecule at boiling point temperature, molecules anywhere in the liquidat boiling point temperature, molecules anywhere in the liquid could escape and vapor pressure equals the environmentalcould escape and vapor pressure equals the environmental pressurepressure sensible heat: sensible heat: we can feel and measure with a thermometerwe can feel and measure with a thermometer Q: Cloud formation [a) warms; b) cools; c) does not change the Q: Cloud formation [a) warms; b) cools; c) does not change the temperature of] the atmosphere?temperature of] the atmosphere?

Q: Why is perspiration an effective way to cool your body?Q: Why is perspiration an effective way to cool your body?

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14Stepped Art

Conduction: heat transfer Conduction: heat transfer within a substance by within a substance by molecule-to-molecule molecule-to-molecule contact due to T differencecontact due to T difference

good conductors: metalsgood conductors: metalspoor conductors: air poor conductors: air

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ConductionConduction

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 do you feel cooler: a) metal; b) wood; c) equal

ConvectionConvection Convection: Convection: heat heat

transfer by mass transfer by mass movement of a movement of a

fluid (such as water and fluid (such as water and air)air)

Thermals: Thermals: rising rising bubbles of air that carry bubbles of air that carry heat upward by convectionheat upward by convection

• Soaring birds, like hawks and Soaring birds, like hawks and falcons, are highly skilled at falcons, are highly skilled at finding thermals.finding thermals.

• Convection (vertical) vsConvection (vertical) vs Advection (horizontal)Advection (horizontal)

Q: why does the rising air expands Q: why does the rising air expands and cools?and cools?

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RadiationRadiation Radiation: Radiation: energy transfer between objects by energy transfer between objects by

electromagnetic waves (without the space between them electromagnetic waves (without the space between them being necessarily heated);being necessarily heated);

packets of photons (particles) make up waves and groups of packets of photons (particles) make up waves and groups of waves make up a beam of radiation; waves make up a beam of radiation;

electromagnetic waveselectromagnetic waves In a vacuum, speed of light: 3*10In a vacuum, speed of light: 3*1055 km/s km/s Wein’s lawWein’s law wavelength at maximum radiation: wavelength at maximum radiation: λλmaxmax = 2897 = 2897

((μμmK)/TmK)/T Stefan-Boltzmann lawStefan-Boltzmann law Radiative energy flux (WmRadiative energy flux (Wm-2-2) : ) : E = E = σσTT4 4

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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

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•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 sunscreenreduces UV-B only

RadiationRadiation

electromagnetic electromagnetic spectrumspectrum

ultraviolet radiation ultraviolet radiation (UV-A, B, C)(UV-A, B, C)

visible radiation visible radiation (0.4-(0.4-0.7 0.7 μμm)m)

shortwave (solar) radiationshortwave (solar) radiation

infrared radiationinfrared radiation

longwave (terrestrial)longwave (terrestrial)

radiationradiation

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vertical scale differs much

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Q: I can see you, because: a) you emit visible light; b) you reflect visible light

Selective AbsorbersSelective Absorbers

Atmospheric window: 8-12 Atmospheric window: 8-12 μμmm

The best greenhouse gas in the The best greenhouse gas in the atmosphere is water vapor, atmosphere is water vapor, followed by COfollowed by CO22

Atmospheric absorption of solar Atmospheric absorption of solar

radiation is smallradiation is small

Atmospheric absorption of infrared Atmospheric absorption of infrared radiation is largeradiation is large

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In general, earth’s surface absorbs almost all infrared radiation. In general, earth’s surface absorbs almost all infrared radiation. If all radiation is absorbed by an object, this object is called “blackbody” and If all radiation is absorbed by an object, this object is called “blackbody” and

earth’s surface is nearly a blackbody.earth’s surface is nearly a blackbody.

Q: does a blackbody need a black color? a) yes, b) noQ: does a blackbody need a black color? a) yes, b) no

Low-level clouds are also good absorbers of longwave radiation (and hence Low-level clouds are also good absorbers of longwave radiation (and hence increase surface air temperature at night) increase surface air temperature at night)

Q: Why do high-level clouds not significantly increase surface air temperature Q: Why do high-level clouds not significantly increase surface air temperature at night?at night?

Q: does ozone strongly affects radiation (see previous two slides)? Answer: No. Q: does ozone strongly affects radiation (see previous two slides)? Answer: No. It absorbs UV below 0.3 It absorbs UV below 0.3 μμm (which contains small amount of solar radiation m (which contains small amount of solar radiation only). It also absorbs infrared radiation around 9.6 only). It also absorbs infrared radiation around 9.6 μμm only.m only.

Q: Does ozone hole affect climate change? a) yes; b) no.Q: Does ozone hole affect climate change? a) yes; b) no.

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Balancing Act - Absorption, Balancing Act - Absorption, Emission, and EquilibriumEmission, 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!

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Zeng (2010; Eos Trans.)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)

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Enhancement of the Enhancement of the Greenhouse EffectGreenhouse Effect

global warming:global warming: due to increase of COdue to increase of CO22, CH, CH44, and other , and other greenhouse gases;greenhouse gases;

global average T increased by 0.6 global average T increased by 0.6 ooC in the past 100 yr;C in the past 100 yr;

expected to increase by 2-6 expected to increase by 2-6 ooC at the end of 21C at the end of 21stst century century positive and negative feedbackspositive and negative feedbacks

• Positive snow feedback: a) increasing temperatures lead toPositive snow feedback: a) increasing temperatures lead tomelting of snow/ice; b) this decreases surface albedo and increases melting of snow/ice; b) this decreases surface albedo and increases surface absorption of solar radiation; c) this increases temperaturesurface absorption of solar radiation; c) this increases temperature

• Potentially negative cloud-temperature feedbackPotentially 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 Warming the Air from BelowBelow

Radiation: Radiation: heat the groundheat the ground Conduction: Conduction: transport heat upward within 1 few cm of groundtransport heat upward within 1 few cm of ground Convection: Convection: transport heat upward within ~1 km of groundtransport 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

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Incoming Solar EnergyIncoming Solar EnergyLight 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 arescattered and only red lightreaches our eyes 27

Scattered and Reflected Scattered and Reflected LightLight

Scattering:Scattering: blue sky, white sun, and red sunblue sky, white sun, and red sun

Reflection:Reflection: more light is sent backwardsmore light is sent backwards

Albedo:Albedo: ratio of reflected over incoming solar radiationratio of reflected over incoming solar radiation

fresh snow: 0.8fresh snow: 0.8

clouds: 0.6clouds: 0.6

desert: 0.3desert: 0.3

grass: 0.2grass: 0.2

forest: 0.15forest: 0.15

water: 0.1water: 0.1

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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.

The Earth’s Annual Energy The Earth’s Annual Energy BalanceBalance

Q: What happens to the solar energy at top of the earth’s Q: What happens to the solar energy at top of the earth’s atmosphere, in the atmosphere, and at surface? A: next slideatmosphere, 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 Q: What is the energy balance at top of the atmosphere, in the atmosphere, and at surface? A: see slidethe atmosphere, and at surface? A: see slide

Q: top: 100 (solar) = 30 (reflection) + 70 (longwave)Q: top: 100 (solar) = 30 (reflection) + 70 (longwave) surface: 51 (solar) = 7 (convection) + 23 (evap) + 21 surface: 51 (solar) = 7 (convection) + 23 (evap) + 21

(net longwave)(net longwave) air: 7 (conv) + 23 (evap)+ 19 (solar) = 49 (net longwave)air: 7 (conv) + 23 (evap)+ 19 (solar) = 49 (net longwave)

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Solar constant = 1367 W/m2

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Heat is transferred by both atmosphere and oceanQ: What is the fundamental driving force of wind patterns in the atmosphere? A: differential heating 32

Why the Earth has SeasonsWhy the Earth has Seasons

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

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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

Seasons in the Northern Seasons in the Northern HemisphereHemisphere

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

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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

While the astronomic winter starts on December 21, meteorological winter season is usually defined as DJF (Dec-Jan-Feb) based on the 3 coldest months

Stepped ArtQ: In Tucson summer, the sun rises from: a) northeast; b) nearly east; c) southeast 36

Computing the maximum solar angle at noon on 21 June at latitude is simply: (90 +23.5 – latitude)

Local Seasonal Local Seasonal VariationsVariations

slope of hillsides: slope of hillsides: south-facing hills warmer south-facing hills warmer & drier& drier

vegetation differencesvegetation differencesQ: Without considering views, Q: Without considering views,

should Tucson homes have should Tucson homes have large windows facing large windows facing a) south; b) north?a) south; b) north?

Q: What would be the answer Q: What would be the answer for a North Dakota home?for a North Dakota home?

a) south; b) northa) south; b) north

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Q: why is the bridge in this figure the first to become icy?