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Lecture 3a: Radiation in the Atmosphere and Climate (Chapter 2)

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Title: Lecture 3a: Radiation in the Atmosphere and Climate (Chapter 2)


1
Lecture 3a Radiation in the Atmosphere and
Climate (Chapter 2)
2
Solar constant and solar radiation
3
Radiation processes in the atmosphere
4
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5
Wave spectrum Short wave Long wave
6
Climate Forcing
The ultimate driving force on the earth the
sun Solar constant is the average solar
radiation that reaches the earth on a
perpendicular plane to the sun ray (total area
?R2) S01368 W/m2 . Short wave radiation (solar
radiation) is normally the average solar
radiation on the surface of the spherical earth
(total area 4?R2) S S0/4342 W/m2 Long wave
radiation (terrestrial radiation) is the back
radiation to the space by the earth with an
effective temperature T as Q?T4 , where
?5.67 ?10-8 W/m2K4 is the Stefan-Boltzman
constant.
7
Blackbody radiation
A blackbody at temperature (in K) radiates energy
at different wave length ? as
where
are constants. The radiation has a maximum value
at the wavelength
?maxa/T, where a2897 ?m K.
Integrated in all the wavelength, we have the
radiation energy flux as E?T4
8
Why tropics is warmer than the poles?
Latitudinal distribution
9
Latitudinal distribution pole-equator
contrast, implication for circulation
10
Why summer is warmer than winter?
Four seasons
11
Why climate is different in different regions
Continental vs Marine Climate
Annual temperature range
12
Land sea contrast Thermal inertial
13
Why the Earth surface temperature is about 15oC
(288K)?
  • Climate modeling
  • Global Mean (0-Dimension) climate model
  • Radiative equilibrium climate models (Lecture 3
    Note. A)

14
Radiative Equilibrium Model
Total heat flux across the surface S - ? T4
0 T c (S/ ?)1/4 , S342 Wm2 ? T c
279oK6oC, Too cold! ,
15
Cloud Albedo Effect Radiative Equilibrium Model
Total heat flux across the surface (1-a)S - ?
T4 0 T cc (1-a)S/ ?1/4 , ? T cc
255oK -18oC Even colder
16
Greenhouse Effect (H2O!)
Heat fluxes surface (1-a)S ? Tg4 - ? T4
0 Top (1-a)S - ? Tg4 0 (or
radiation balance for the glass layer 2? Tg4
? T4 ) Tg ((1-a)S/ ?)1/4 Tcc255K , ? Tcg
21/4Tg288oK15oC About right
17
How does the climate respond to global warming
forcing?
CO2 induced Radiative Forcing Climate Sensitivity
18
CO2 induced Radiative Forcing
  • RF 5.25 ln (CO2) W/m2 (S.
    Arrhenius, 1900)
  • Examples Present relative to 1850 (CO2 250ppm)
  • RF5.25 ln (385 / 250 ppm) 2.5 W/m2
  • Doubliing CO2
  • RF5.25 ln (500 / 250 ppm) 4 W/m2

Climate Sensitivity ?TbRF b
climate sensitivity! increase in
temperature per unit increase in
radiative forcing
19
Svante Arrhenius
Born 19 February 1859(1859-02-19) Vik, Sweden
Died 2 October 1927(1927-10-02) (aged 68) Stockholm, Sweden
Nationality Swedish
Fields Physics, chemistry
Institutions Royal Institute of Technology
Alma mater Uppsala University Stockholm University
Doctoral advisor Per Teodor Cleve, Erik Edlund
Doctoral students Oskar Benjamin Klein
Known for Arrhenius equation Theory of ionic dissociation Acid-base theory
Notable awards Nobel Prize for Chemistry (1903) Franklin Medal (1920
20
Global Warming Response Radiative Equilibrium
Model
RF(CO2)
Global warming prediction
Total flux S RF- ? T4 0 T (SRF)/
?1/4 (S/ ?)1/4 bRF Tc bRF,
here RFltltS or global warming ?T T- Tc
bRF Climate sensitivity bd (S/ ?)1/4 /dS
1/(4 ?Tc 3)0.2 K / Wm-2 ? Double CO2
?T bRF 0.2 4 0.8oK, small??
21
Cloud Albedo Effect Radiative Equilibrium Model
Total heat flux across the surface (1-a)S RF-
? T4 0 T cc (1-a)S/ ?1/4 , ? T cc
255oK -18oC Climate sensitivity b1/(4
?Tcc 3)0.37 K / Wm-2 Double CO2 ?T
bRF 0.37 4 1.5oK greater
!
22
Greenhouse Effect (H2O!)
Heat fluxes surface (1-a)S RF-? Tg4 - ?
T4 0 Top (1-a)S RF-? Tg4 0 T
cg 2(1-a)S/ ?1/4 288oK15oC Now climate
sensitivity , b1/(4 ?Tcg 3)0.45 K /
Wm-2 Double CO2 ?T bRF 0.45 4
1.8 2oK, even greater !
23
Svante Arrhenius
To explain the ice age, Arrhenius estimated that
halving of CO2 would decrease temperatures by 4 -
5 C (Celsius) and a doubling of CO2 would cause
a temperature rise of 5 - 6 C. In his 1906
publication, Arrhenius adjusted the value
downwards to 1.6 C (including water vapour
feedback 2.1 C). Recent (2007) estimates from
IPCC say this value (the Climate sensitivity) is
likely to be between 2 and 4.5 C. Arrhenius
expected CO2 doubling to take about 3000 years
it is now estimated in most scenarios to take
about a century.
24
Lecture 3b Heat Transfer in the
Atmosphere (Chapter 2)
25
Convection, Stratification
26
Latitudinal Differential Heating-- The driving
force for circulation
27
Atmospheric General Circulation
28
Rotation
29
Coriolis force
30
Monsoon, precipitation
31
monsoons
32
Subtropical High
H
Geostrophic flow
33
Surface temperature, Clouds
Extratropical cyclones
Tropical convection
Extratropical cyclones
34
Infrared Images
Extratropical cyclones
Tropical convection
Extratropical cyclones
35
Water vapor content
36
Extratropical Cyclone, Storm Track
Infrared (long wave)
Visible light (short wave)
Water vapor
37
Regional climate Regional topographic effect
38
Vertical structure of the atmosphere
39
Vertical mass distribution
Troposphere
40
The Role of Water Fuel for the Climate Heat
Engine Hydrological Cycle
41
Latent heat of melting and vaporization
42
Water vapor content
43
Lecture 3c Heat Transfer in the Ocean (Chapter
2)
44
Ocean Circulation, Ocean Gyres
45
How does wind drives the ocean?
Ekman flow Ekman spiral Ekman layer
46
Ocean gyres
47
Vertical temperature structure Thermocline
48
Wind-driven Upwelling
49
Overturning circulation
50
Thermohaline circulation
51
Thermo--haline circulation
Equator Saline
North Pole Fresh
Equator Warm
North Pole Cold
Haline circulation
Thermal circulation
Thermo-Haline circulation
52
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53
Schematic figure of various branches of climatic
teleconnections in the atmosphere and ocean. The
atmospheric teleconnections occur at fast time
scales, usually shorter than monthly to seasonal
(not marked). The oceanic teleconnection occurs
at a wide range of time scales as marked.
54
Lecture 3d Climate Modeling (Chapter 2)
55
Climate Modeling
  • General Circulation Model
  • Energy Balance Model
  • (L3 Note.B)

56
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57
CCSM3 (T31_gx3v5) Dyn Veg
TRACE-21 Experiment Set Up
  • Atmosphere (CAMT31)
  • 3.75o x 3.75o x 26 level
  • Ocean (POPSea Ice)
  • 3 to 0.5o on equator
  • Land (CLMLPJ)
  • Forcing
  • realistic orbital, GHGs,
  • continental ice sheet (ICE-5G, each 500-yr)
  • land sea mask (twice)

Meltwater No. 1 uncertainty!
58
Earth System Model
Biogeochemical Cycle (e.g. Carbon cycle)
59
Test Climate Model Climate Sensitivity
  • From last glacial era, we know this is roughly 5
    C per 7 W/m2
  • glacial to post-glacial
  • This amounts to 0.75 C / W m-2
  • IPCC says for doubling of CO2, should expect 1-6
    C of warming

60
LGM Climate
CLIMAP SST
Model SST
Model Tair
1) CO2 vs. ice sheet 2) Proxy uncertainty vs.
model uncertainty
Liu et al., 2002, GRL
61
The End Lecture 3
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