1
RadiationLecture by Bert Heusinkveld(thanks to Bert Holtslag&Leo Kroon)
Meteorology and Climate: Module 4 (Jan 9, 2019)
Basics of Solar and Terrestrial RadiationAlbedo, emissivityGreenhouse Effect
Atmospheric Optical Effects(blue sky, rainbow, halo)
Radiation Balances
2Radiation
Clouds
Precipitation
Moisture
&
Stability
Heat
Atmospheric Dynamics
&
Rotations
Models & Prediction
Boundary Layer
Climate
Today’s Temperatures and Precipitation
(www.knmi.nl)
3
4
Satellite picture at 10.30 UTC (www.knmi.nl)
5
Weather Map 06 UTC (7 h local time)(www.knmi.nl)
6
Weather Map 12 UTC (13 h local time)(www.knmi.nl)
Thunderstorms in Europe? https://www.lightningmaps.org/
Mistral: Ventusky
Wind from the north:https://earth.nullschool.net/
Winter coming? 8
Web link:ECMWF T anomaly
9Weather and Forecasting
Temperature Forecast Plume starting Jan 9, 2019 (KNMI)
Long term record maximum temperature
Long term record minimum temperature
Long term mean max and min temperature
10Weather and Forecasting
KNMI forecast plumes: klimaatpluim
11
Surface Weather at Wageningen(www.maq.wur.nl)
Veenkampen weather stationhttp://www.met.wur.nl/veenkampen/Graphs/Cur/graphs.html: website
12The electromagnetic spectrum (Fig 4.1)
13
Orbital factors
The electromagnetic spectrum and wave lengths
hE
c
c
/
][31.0. mradwaveshort
][503. mradwavelong
speed of light (2.998 x 108 m/s)
frequency (1/s)
energy photon (J)
h is Planck's constant(h = 6.626 × 10-34 J.s)
15
Radiation black body given by Planck’s law
Planck’s law
Blackbody radiative emissiondepends on wave length and
temperature
1)(
)(
5
1
2
Tc
e
cTB
See MetClip 4a!
16
T = 6000 K T=255 K
Shortwave radiation Longwave radiation
17
Black body: Wien’s law about the wavelength of peak emission
Radiation black body given by Planck’s law
Radiation laws
][2897
max mT
18
This would imply ~ 5000 K
][622.0577.0 morangeyellow
But, melting iron ~ 1800K
Why can we see it anyway?
][2897
max mT
Radiation is not only emitted near maximum
19
Black body: Stefan-Boltzmann law about TOTAL amount of emission by Black body:
T in Kelvin!!
Radiation laws
4* TE
428 /1067.5 KmW
20
Generally Non-black body:
Radiation laws
**
blackbodyEE
If emissivity is not dependent on wavelength we have a so-called grey body:
4** TEE blackbodygreybody
Most natural surfaces:
Atmosphere (clear to cloudy skies):
1
0.16.0
21Distance to the sun important
for radiation top atmosphere
Inverse square law (W&H 4.7):
𝐹 ∝1
𝑟2
22
Orbital factors
(1 Gm=1 billion m = 1 million km)
23
Orbital factors
Earth’s orbit around the sun is elliptic
and disturbed by moon!
4 July(farest
distance)
3 Jan(closest
distance)
Impact of moon orbit on earthHere illustrated for water on earth (not to scale)
24
Thanks to Wouter Holtslag and Jacob van Berkel
25
Module 2 Radiation
Position of the sun
Perihelion (3 Jan): Earth –Sun distance
smallest
Aphelion (4 July): Earth-Sun distance
largest
At the solstice the tilt of the Earth's axis is most inclined toward or away from the Sun(above Tropic of Cancer in NH or Capricorn in SH)
27Average daily insolation (MJ/day m2) top atmosphere
(Figure 10.5, p 423 book)
1 MJ/day m2
=11.57 W/m2
Thus more insolation in Dec-Jan!
(earth closer to the sun)
28Planet Earth
Receiving Solar Radiation, butreflecting part by Clouds andSurface: ALBEDO
Albedo on average ~30% for Earth and Atmosphere
(average cloud fraction: 60% for land area and about 70% for ocean area)
Albedo on average ~15% for clear skies only
30Global mean radiation balance top of atmosphere
CK
SAT
eº18255
4
14
S= 1368 Wm-2
Solar constant
2)1( RSA In
albedo Normal area
424e
TR Out
Effective radiation temperatureTotal area
A, Albedo: 30%for Earth andAtmosphere
R drops outWhat happens forlarger S or A?
𝟏 − 𝑨 𝑺 = 𝟒𝝈𝑻𝒆𝟒Radiation balance:
31Radiation balance with an Atmosphere
4
122
41
44
4
SATT
TS
A
as
a
Suppose the atmosphere is
• transparant for Solar radiation• not transparant for longwaveradiation (thus the air emissivity=1)
Factor 2 represents “Greenhouse-effect” due to presence of atmosphere!
This simple model gives: Ts= 303 K = 30ºC...
Top atmosphere:
Balance atmosphere:
32Radiation
(at clear skies!)
Absorption dependson wave length and(trace) gases!
Atmospheric ‘Window’ for 8 – 14 micron:Longwave radiation canescape through atmosphere
Shortwave (Solar)
Longwave (Earth and
Atmosphere)
33Radiation Balance including an Infrared window
Emissivity coefficient ofthe atmosphere e1
CKTe
AS
eT
s
s
º172908.0
142
24
Cº16nsobservatio From
Note: There are also other processes active than radiation(see later in this lecture)
Top:
𝝈𝑻𝒔𝟒 =
𝟎. 𝟐𝟓𝑺 𝟏 − 𝑨 − 𝒆𝝈𝑻𝒂𝟒
(𝟏 − 𝒆)
𝝈𝑻𝒔𝟒 =
𝟎. 𝟐𝟓𝑺 𝟏 − 𝑨 𝟐 − 𝒆𝝈𝑻𝒔𝟒
𝟏 − 𝒆 𝟐
𝟐 𝟏 − 𝒆 𝝈𝑻𝒔𝟒 + 𝒆𝝈𝑻𝒔
𝟒 =𝟐𝑺 𝟏 − 𝑨
𝟒
𝝈𝑻𝒔𝟒 𝟐 − 𝟐𝒆 + 𝒆 =
𝟐𝑺 𝟏 − 𝑨
𝟒
𝟏 − 𝒆 𝝈𝑻𝒔𝟒 + 𝒆𝝈𝑻𝒂
𝟒 =𝑺
𝟒(𝟏 − 𝑨)
𝟐𝒆𝝈𝑻𝒂𝟒 = 𝒆𝝈𝑻𝒔
𝟒
Note: atmosphere fully transparent for solar radiation!
Atmosphere:
Now calculate Ts:
34
FAQ 1.3, Figure 1Greenhouse effect = Atmosphere effect!
35
Earth, Venus and Mars
427
Why is greenhouse effect so much stronger on Venus?
36
The solar constant isn’t …
Last 30 years on average S~1366 W/m2
https://www.pmodwrc.ch/en/research-development/solar-physics/tsi-composite/
37
Position of the sun
Definitions: sun position angles
Zenith (above observer O)
Zenith angle(angle with zenith)
Sun elevation angle(angle with the surface)
Azimuth (angle from the North)
38
Position of the sun
Dec
June
May/July
Sept/Mar
Oct/feb
Nov/Jan
Aug/Apr
180
Centre=Zenith, Circles: Sun angles
Local solar time
39
Position of the sun
Combine with Fish Eye photo to examine Shadowing at certain location
40Break
41Great Wall of China just after sunrise (Fig 4.14)
What explains these colors?
42Absorption, Reflection and Transmission
a + r + t = 1I r I
a I
I
reflected
absorbed
transmitted
See MetClip 4b!
43Extinction of radiation in atmosphere (Fig 4.10)
Due to scattering and absorption of molecules, aerosols, cloud
particles, etc: Attenuation depends on wave length and particle size
dz
ds
s
N
K
I
dsNKIdI
cos
1sec
:
:
:
:
: Radiation Intensity
Scattering efficiency
Number of particles/m3
Areal cross section
Distance in direction of beam
44Atmospheric particle size (r) and wavelength
determine type of scattering (Fig 4.11)
rx
2
Dimensionlesssize parameter
45
Scattering of visible radiation ( )
Fig. 4.12
)(10 4 rmr)(1.0 rmr
)(1 rmr
m 5.0
Mie scattering
Rayleigh scattering
47Rayleigh scattering and atmospheric colors
Rayleigh scattering most effective for blue: 1) Sky is blue above due to scattering of air molecules
2) After a long atmospheric path (at sunrise) most blue is depleted and red remains
45.347.0
64.0
)(
)(
)(64.0
)(47.0
4
4
redK
blueK
redm
bluem
K
Scattering efficiency:
Scattering
51
Roy Lichtenstein, Sunrise, 1965
Atmospheric radiation effects on Mars52
Sun set on Mars
Observations by the Mars Sounder “Curiosity”
Daytime atmosphere on Mars
(relatively more aerosols,
less molecules than on earth)
http://www.nasa.gov/mission_pages/msl/index.html
53Primary and Secondary Rainbows (Fig 4.15)
54Refraction of light by raindrops (Fig 4.16)
Raindrops act like a prismgiving component colors
Secondary rainbow bydouble reflection
(8 degrees above primary)
55Formation of Haloes by ice crystals (Fig 4.17)
56Refraction of light in hexagonal ice crystals and
the 22 and 46 degrees halos (Fig 4.18)
58
SunSundog
Very often a Sundog if Cirrus is present!
(part of Halo)
59
Two Views of the limb of
the Earth from Space
(Fig 4.36, p 146)
with upper blue sky and
lower orange pure colour
Lower photo taken 2
months after Pinatobo
eruption shows layers of
aerosols in lower
stratosphere
Why is the universe black?
61
Figure 4.34:
Annual mean
absorbed solar and
outgoing longwave
radiation at top of
atmosphere
62Figure 4.35: Annual mean net radiation at top of
atmosphere
63
Global average of net radiation top and bottom atmosphere
Net radiation: Q0* = K0- K0
- L0
Global average: 0 = 100 - 31 – 69 (%)
Radiation balance
Net radiation : Q* = K- K + L - L
Global average: 30 = 49 – 19 (%)
No radiation balance
64
after Kiehl and Trenberth (1997)
Earth´s annual global mean energy budget
31% 100%69%
65Cloud Effects on Earth’s Energy Budget
66
Short & Longwave Only Longwave
Radiation: Day and Night
67Diurnal cycle surface radiation budget
Components radiation balance obtained by the Meteorology group (WUR),
Kansas, U.S.A.
-100
0
100
200
300
400
500
600
700
800
Time
350
750
1150
1550
1950
2350 35
075
0
1150
1550
1950
S_in
S_out
L_in
L_out
Rnet
clouds
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Surface radiation budget Wageningen (Monday Jan 8, 2018)
www.maq.wur.nl
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Sunshine duration Wageningen (Monday Jan 8, 2018)
www.maq.wur.nl
70Measurement of solar radiation
Extraterrestrial radiation
TOA
Direct beam atnormal incidence
Direct beam atthe horizontal plane Diffuse radiation
Total = direct + diffuse
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Surface radiation budget Wageningen (Monday Jan 8, 2018)
www.maq.wur.nl
72Wageningen 80 year Observations
Annual solar incoming radiation at surfaceArrows indicate major volcanic eruptions
74Application: Solar Energy
76Long wave Radiation effects often visible in nature
Frost and dew
77
Buildings also produce longwave radiation
contributing to Heat Stress in Summer
78Summary
Basics of Solar and Terrestrial radiation
Kirchhoff’s law,
Greenhouse effect
Scattering, Absorption and Emission
Radiation balance
Monday’s test
Test is on PC and is 1 hour total in 2 parts:
. First part is closed book
. Second part open book: Bring book and reader!
Once you start with second part, you can not return to first part
Dictionary is also allowed! Use calculator of PC
Note final exam is still on paper!
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