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!

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Earth, Venus and Mars

427

Why is greenhouse effect so much stronger on Venus?

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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

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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

68

Surface radiation budget Wageningen (Monday Jan 8, 2018)

www.maq.wur.nl

69

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

71

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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