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Appendix A

Appendix A. Length: m 1 km = 1000 m; 1 m = 100 cm = 1000 mm = 10 6 micrometer ( μ m) 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 Q: 10 μ m = ? a) 10 -5 m; b) 10 -6 m; c) 10 -7 m.

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Appendix A

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  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. = 12*2.54 = 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 = 20*1.6 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 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 • 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; 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 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: 3*105 km/s • Wein’s law λmax = 2897 (μmK)/T • Stefan-Boltzmann law E = σT4 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 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 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, earth’s 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 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)

  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 earth’s axis • Earth-sun distance has little effect on atmospheric temperature. • Q: if the earth’s 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

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