solar radiation, earth-sun geometry and climatology
TRANSCRIPT
Lecture 7Solar Radiation, Earth-Sun Geometry and , y
Climatology, part III
• Lambert's cosine law• Lambert s cosine law• Earth-Sun geometry
– Earth declination, elevation, zenith, hour and azimuth angles– seasons– sunrise and sunset times
• Radiation Climatology and Functional Relations for gy‘Weather Generation’
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Lambert's cosine law
Definition of zenith and elevation angles and the projection of area normal to incident rays on a flat surface
R i R AA
beam
horizontal
( )
Zenith Angle
horizontal
Elevation angle
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R A cos( ) sin( )horizontalR AR C
B
AC
A A
B
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Cosine of solar zenith angleCosine of solar zenith angle
1.0
) 0.6
0.7
0.8
0.9
cosin
e(
0 2
0.3
0.4
0.5
0.6
Solar Zenith Angle (degrees)
0 20 40 60 80
0.0
0.1
0.2
Values vary non-linearly between 1 and zero
g ( g )
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Values vary non linearly between 1 and zero
S l El i ( ) d Z i h ( ) A lSolar Elevation () and Zenith () Angles
sin( ) sin( )sin( ) cos( )cos( )cos( ) cos( ) h
is latitude, h is the hour angle and is declination angle.
Units: Radians!Units: Radians!
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Vectors describing the angle between the sun and a point on EarthVectors describing the angle between the sun and a point on Earth
S n
S
n
n S n n S n ( ) | ||( )|cos
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n S n n S n( ) | ||( )|cos
t t2 h t t
224 12
Earth rotates on its axis 2 radians in one day
Hour angle, h, is the fraction of 2 that the earth has turned after local solar noon:
h t t 12 0( )
(radians)12 ( )
t l ec t0 12
lc, longitudinal correction
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et, equation of time
lc is the longitudinal correction.lc is the longitudinal correction.
• 4 minutes for each degree of longitude east of the standard meridian
4 i t f h d f l it d t f th• - 4 minutes for each degree of longitude west of the standard meridian
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Longitudinal Correction
120105
90
75
60
45
30
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Equation of Time hours
L O
Equation of Time, hours
e f f f f f f ft
LNM
OQP
104 7 596 2 2 43 3 12 7 4 4293 2 0 2 193 33600
. sin( ) . sin( ) . sin( ) . sin( ) . cos( ) . cos( ) . cos( )
f d
180279 5 0 9856. . radians
Campbell and Norman, 1998
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p ,
Equation of timeEquation of time
urs
) 0.2
0.3
n o
f T
ime
(hou
0.0
0.1
Equati
on
-0.2
-0.1
Day
0 50 100 150 200 250 300 350
-0.3
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Values of h and cos(h) for several reference valuesValues of h and cos(h) for several reference values
Solar time (hour) h (radians) Cos(h)6 0 5 06 0.5 0
12 -1
18 1.5 01.5
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Geometrical configuration between the Sun and th E th d i th S S l tithe Earth during the Summer Solstice
Equator
Tropic of Cancer
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Earth and Sun Geometry during the Spring and Autumnal Equinoxy g p g q
Spring/AutumnalEquinox
Tropic of Cancer
Equator
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Configuration between the Sun and Earth during the Winter solstice g g
Winter Solstice
Equator
Tropic ofCapricorn
Equator
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Basic Earth/Sun Geometryas c a t /Su Geo et y
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Lutgens/Tarbuck, Atmosphere
Solar Declination Angle, radians
2 10( )D
2345180
2 10365
. cos( ( ) )D
D, day of year
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Seasonal variation in the declination angle
20
30n
Ang
le 10
Dec
linat
ion
-10
0
-20
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0 50 100 150 200 250 300 350-30
Solar elevation and azimuth angles at Sisters, OR (44o N) f d i t l ti d th ifor summer and winter solstices and the equinoxes
90
40
50
60
7060120
10
20
30
4030150
0 10 20 30 40 50 60 700
0102030405060700
10
20
0180
30
40
50
210 330
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60
70240
270
300
Solar elevation and azimuth angles at Oak Ridge, TN (36o N) for summer and winter solstices and the equinoxes
Oak Ridge, TN
70 60
90
120 36 oN
30
40
50
60
30150
0 10 20 30 40 50 60 700
10
20
0102030405060700
10
0180
20
30
40
50
210 330
60
70240
270
300
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Time of Sunrise/Sunset
sin( )sin( ) cos( )cos( )cos( ) h 0
cos( ) tan tanh
h 180h 180t t hsunrise 12 15
180
t t hsunset 12 15
180
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ESPM 129 Biometeorology 22Zachos et al Science 2001
Magnitude and Seasonality in Rg
Oak Ridge, TN199630
35
m-2
d-1
)
20
25
30
daily
sum
(MJ
m
10
15
20
Rg d
0
5
Day
0 50 100 150 200 250 300 350
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I CA
Estimating Solar Radiation as f(Tair and VPD)
Ione, CA
25
30
35m
-2 d
-1)
5
10
15
20
35ar R
adia
tion
(MJ
0
5
510
1520
2530
23
45
6
Sola
T air (C
)
0-1
01VPD (kPa)
R MJ m d T VPDg air( ) . . 2 1 0947 1033
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FLUXNET database
8000
J m
-2 y
-1) 6000
Rg
(M
2000
4000
0 10 20 30 40 50 60 70 80 900
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Latitude
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Credit: Youngryel Ryu
How Does Energy Availability Compare with Energy Use?gy y p gy
• US Energy Use: 105 EJ/yeargy y– 1018J per EJ– US Population: 300 106
– 3.5 1011 J/capita/year• US Land Area: 9 8 106 km2=9 8 1012 m2 = 9 8 108 ha• US Land Area: 9.8 106 km2=9.8 1012 m2 = 9.8 108 ha• Energy Use per unit area: 1.07 107 J m-2
• Potential, Incident Solar Energy: 6.47 109 J m-2
– Ione, CAIone, CA• Assuming 20% efficient solar system
– 8.11 1010 m2 of Land Area Needed (8.11 105 km2, the size of South Carolina)
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Ivanov et al 2008 WRR
Rn as a f(Rg)
800
600
800
Temperate broadleafRn=-23+0.86Rg
Rn
(W m
-2)
400
0
200
Boreal jack pineRn=-27+0.897Rg
Rg (W m-2)
0 200 400 600 800 1000
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Rn = a + b Rg
intercept (W m-2)
slope vegetations source
-73.85 0.787 Zea mays Davies and Idso (1979)
-29 0.842 boreal forest Dubuyah
-27 0.897 Pinus banksiana
ddb + CV
-23 0.860 deciduous forest
ddb +cvforest
-66 0.86 Picea sitchensis
Jarvis et al. (1976)
-110 0.87 Pinus taeda Jarvis et al. (1976)
38 0 91 Pi J i t l (1976)-38 0.91 Pinus sylvestria
Jarvis et al. (1976)
-63 to -124 0.655 to 0.808
wheat Denmead (1976)
-91 0.72 grassland Ripley and Redman (1976)
-60 0.85 Ponderosa pine, OR
Anthoni (unpublished
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Ione CAIone, CA
40m
-2 d
-1
30
35
ncom
ing,
MJ
m
25
20
30
Long
wav
e In
rC
20
0
10
01
23
Tair,
VPD, kPa
ESPM 129 Biometeorology 32
SummarySummary
• Lamberts cosine law describes the amount of radiation received on the horizontal relative to the sun’s zenith anglethe horizontal relative to the sun s zenith angle.
• The amount of radiation received on an inclined surface is a function of the angle between the sun the that projection normal to the surface.
• The axis of rotation of Earth is tilted 23.5 degrees• The amount of radiation received is a function of its latitude and the
sun’s declination angle.• Seasons arise as the Earth revolves around the sun because the• Seasons arise as the Earth revolves around the sun because the
Earth’s tilted rotation axis causes the shaded and sunlit faces of Earth to change.
• Radiation fluxes can be estimated empirically with weather variables lik t t d h iditlike temperature and humidity
ESPM 129 Biometeorology 33