Chapter 1: Earth with no Atmosphere (no rotation) - Introduction - Kepler Laws - Milankovich Theory - Seasons - Energy Balance Chapter 2: Earth with

Transcription

1 Topics covered in Course: Chapter 1: Earth with no Atmosphere (no rotation) - Introduction - Kepler Laws - Milankovich Theory - Seasons - Energy Balance Chapter 2: Earth with Atmosphere (no rotation) - Atmospheric Composition - Water Vapor - Clouds and Climate - Radiation (SW and LW) - Scattering Chapter 3: Vertical Motions in Atmosphere (no rotation) - Thermodynamics - Lapse Rates - Atmospheric Layers - Instability - Clouds and Rain formation Chapter 4: Horizontal Motions in Atmosphere (with rotation) - General Circulation - Coriolis Force - Atmospheric Winds - Jet stream - Ocean currents - Storms Chapter 5: Global Issues (Science, Society and Politics) - Ozone Hole - Global Warming

2 Atmospheric Composition הרכב האטמוספירה

3 O 2 Trace Gases N 2 Water Vapor (H 2 O) Argon (Ar) Carbon Dioxide (CO 2 ) Neon (Ne) Helium (He) Methane (CH 4 ) Nitrous Oxide (N 2 O) Ozone (O 3 )

4 Nitrogen and oxygen concentrations experience little change, but carbon dioxide, methane, nitrous oxides, and chlorofluorocarbons are gases experiencing great increases in concentration.

5 ppm % Real Air

6 Why so much Nitrogen? It is volatile in most forms Eg. Ammonia gas It is unreactive with most solid earth material It is stable in sunlight. Why so much Oxygen? Produced by photosynthesis. Why so much Argon? It slowly degasses from rocks It is unreactive so stays in the atmosphere Argon is a noble gas Why so little carbon dioxide? Original atmosphere was probably about 25% CO 2 It dissolves in water It is used by plants in photosynthesis

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8 מחזור ההידרולוגי Water : The Hydrological Cycle

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11 יחס עירוב m Mixing Ratio w v = m d mass of water vapour mass of dry air [g/kg] Dry regions ~ 1 g/kg Tropics ~ 20g/kg = q Specific Humidity: לחות סגולית w + m d 1 + w m v m v Since m v << m d q~w Specific humidity NOT dependent on volume

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13 When evaporation = condensation w = w s w w s Saturation mixing ratio: w s m vs m d (mass of w.v. in saturated volume) Sat. vapor pressure e s depends only on T de s = L e s dt R v T 2 e, T are values at the phase change e s = e o exp (- L ) v R v T Clausius Clapeyron Equation L v = latent heat of vaporization per unit mass (2.25x10 6 Jkg -1 ) R v = Gas Constant for water vapor

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15 Clausius Clapeyron Curve נקודת הטל Dew point Temp. RH=100%.

16 Measurements of the Vapor Pressure in the Atmosphere

17 Relative Humidity RH = 100 w = 100 e [%] לחות יחסית w s e s RH is the ratio between the mixing ratio measured relative to the saturation value Dewpoint condensation of vapour to liquid

18 טמפרטורת נקודת הטל Dew Point Temperature: The temperature the air needs to be cooled in order to reach saturation (RH=100%) is called the dew point temp T d. Dry air T T d large Moist air T T d small Rule of thumb: T T d (100-RH) 5 If RH=85% T-Td ~3C Td T If T-Td = 15C RH ~ 25%

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20 RH=100% הטל נקודת Dew point Temp. q=14g/kg RH~90% q=14g/kg RH~60%. q=4g/kg RH~90%

21 Warm air can absorb more vapor than cold air, so for a given parcel of air, specific humidity declines from its highest in the tropics to its lowest in the colder poles. Desert air, at 30, however, is not more saturated than polar air.

22 How can we reach saturation in atmosphere? Add moisture

23 CONTRAILS (Condensation Trails)

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25 Evaporation Fog

26 Cool air

27 Fog ערפל

28 Radiation Fog Occurs at the ground when dew point temperature is reached by radiational cooling.

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30 Advection Fog Warm moist air that moves, or advects, above a cold surface may become cooled to its dew point temperature, creating an advection fog.

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32 Dew טל frost קרה T>0C T<0C

33 Mixing of Air Parcels

34 טמפרטורה הגולה הלחה ) w Wet Bulb Temperature (T The measurement of the air temperature will decrease by evaporation until it reaches saturation. Heat from the air evaporates water on the wet bulb, increasing the mixing ratio around the thermometer cooling air. At saturation T w there is no more evaporation, and therefore the air stops cooling RH=69% T d T w T In practice T w ~ T d +T 2

35 Psychrometer

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37 Solar and Terrestrial Radiation Electromagnetic Radiation קרינה אלקטרומגנטית E= h/λ c=

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39 Click to edit Master text styles BLACKBODY RADIATION Second level Plank s Law describes the radiation of a blackbody Third as a level function of temperature and frequency. It is derived Fourth from level the probable molecular energy distribution at a given temperature. Fifth level» B (T) = 2ħ 3 c 2 e ħ /kt - 1 Where: ħ = Plank s const.=6.624x10-34 Js c = speed of light=3x10 8 ms -1 k = Boltzman s const.=1.37x10-23 JK -1 T = temperature (K) = frequency (s -1 )

40 Stefan-Boltzman law: The integral of the Plank function over all frequencies. B(T) = B (T) d = T 4..and can be expressed in terms of a flux F = T = 5.67 x 10 W m K

41 Wien s Displacement Law: wavelength of maximum emission is inversely proportional to temperature. The hotter the object, the higher the frequency and the shorter the wavelength of emitted radiation. When db/d = 0 max = 2897 T [ in m]

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43 Kirchoff s Law: Good absorber is also a good emitter

44 How do we know the temperature of the Sun? Wavelength of Maximum Solar Energy = max =0.5 micron (10-6 m) Wien s Law: max =2897 T (micron = m) T = 2897 max (K) T (sun) ~ 6000 K

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48 Solar Radiation Radiation from the sun (photosphere) is essentially continuous similar to a blackbody at ~6000 K, although a bit less, particularly around 0.3 m and less.

49 Electromagnetic spectrum: Most of the radiation from the sun (99%) is between the wavelengths of 0.15 m and 4 m, and is called shortwave radiation. Of this 9% is in the UV ( < 0.4 m), 45% is in the visible ( m), and 46% in the infrared ( > 0.74 m).

50 Earth: T e = 15 C = 288 K => max = 10 micron

51 Short Wave (SW) Long Wave (SW) T sun = 6000K T e = 288K

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53 Earth s energy budget (averaged over the whole globe and over a long time) At the top of the atmosphere: Incoming shortwave = Reflected Shortwave + Emitted longwave At the surface: Incoming shortwave = Reflected shortwave + Net emitted longwave (emitted - incoming) + Latent heat flux + sensible heat flux Yellow: shortwave Red: longwave Sensible heat 7% Net Longwave 21% Latent heat 23%

54 2/3 albedo from clouds

55 Clouds Influence on the Climate

56 החזרת SW לחלל March 2000 בליעת LW באטמוספרה

57 השפעת עננים על SW השפעת עננים על LW Clouds have 2 opposing effects on the radiation balance

58 High Cirrus Clouds עננים גבוהים Warm the Earth חימום של כדור הארץ

59 Low stratus/cumulus clouds עננים נמוכים Cool the Earth קירור כדור הארץ

60 Deep Convective Clouds ענני סערה - קונבקטיבים No net influence on Surface Temperature לא משפיע על טמפרטורת כדור הארץ

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62 Without clouds the Earth would be warmer בלי עננים כדור הארץ היה חם יותר ~20C warmer

63 Impact of Clouds on Climate on radiation balance חימום קירור

64 Atmospheric influences on radiation Absorption (absorber warms) Reflection Scattering

65 פיזור אור Atmospheric Light Scattering Scattering is the redirection of energy. No energy is absorbed Reflection is a special case of scattering All substances reflect light with varying effectiveness (the albedo of the substance)

66 פיזור ריילי Rayleigh Scattering When >> particle radius (eg. O 2 and N 2 ) Intensity of scattered light: R is distance to particle is scattering angle n is refractive index of particles is wavelength of radiation d is diameter of particles For molecules of air no refractive index, but rather a polarization index

67 Why is the sky blue? I s ~ 1 4 short long Rayleigh Scattering is equal in all directions

68 פיזור ריילי

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70 Rayleigh Scattering The Earth has an atmosphere. So it has Rayleigh scattering and its sky appears blue The Moon has no atmosphere. So it has no Rayleigh scattering and its sky appears dark

71 Rayleigh scattering also explains reddish-orange sunsets when light travels through thick slice of atmosphere

72 הבזק ירוק Green Flash

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75 ליקוי הירח ירח אדום Lunar Eclipse Red Moon

76 פיזור מי Mie Scattering Scattering by aerosols in atmosphere, where ~ r particle size (eg. Dust, cloud drops, air pollution) Scatters forward predominately No dependence on wavelength reason for white clouds

77 Solid particles air pollution Cloud drop scatter all wavelengths equally

78 Polluted Air How does air pollution (particles) More drops impact cloud albedo? Higher Albedo Clean Air Less drops Lower Albedo אוויר מזוהם יותר טיפות עליה באלבדו אוויר נקי פחות טיפות ירידת באלבדו

79 A~0.7 A~0.9

80 Ship Tracks

81 Ship tracks produced by pollution from ship chimneys

82 עננים יותר בהירים

83 x 2 r

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85 What have we learned?? The atmosphere is made of mainly N 2 and O 2 with a little water vapor (~1%) The saturation vapor pressure (RH=100%) depends on temperature and the absolute amount of water vapor in the air (Clasius- Clapeyron) The amount of energy emitted by a body (sun, earth, cloud) depends only on that body s temperature (Stefan-Boltzman Law) The wavelength of maximum radiation is also determined only by the temperature of the body (Wien s Law) High clouds tend to warm the Earth s climate while low clouds tend to cool the climate In the atmosphere, solar radiation is scattered either by Rayleigh scattering (blue sky) or Mie scattering (white clouds)