10-1
The Sun - Driving Force for
Climate
Physical Climate Systems
Climate
Change
Stratospheric
Chemistry/Dynamics
Sun
Volcanoes
Ocean
Dynamics
Terrestrial
Energy/Moisture
Global Moisture
Marine/
Biogeochemistry
Soil
Terrestrial
Ecosystems
Tropospheric Chemistry
Biogeochemical Systems
Human
Activities
CO2
Human Forcing
External Forcing
Atmospheric Physics/Dynamics
Land
Use
CO2
Pollutants
Climate and Global Change Notes
The Sun - Driving Force for
Climate
Solar Radiation and Its Variability
10-2
Science Concepts
The Sun
Solar Radiation Source
Nuclear Fusion Process
Einstein’s E = m c2 Law
Solar System
Sun Spots
1/R2 Law
Intensity
Angle of Incidence
Spherical Shape of Earth
Axis of Rotation
Orbital Plane
Solar Radiation Variability
Solar Output Variations
Planet-to-Planet Variations
Latitudinal Variations
Seasonal Variations
Long-Term Variations
Milankovitch Cycles
Eccentricity
Precession
Obliquity
The Earth System (Kump, Kastin & Crane)
•
•
Chap. 1 (pp. 14-15)
Chap. 15 (p. 303-306)
•
•
Chap. 4 (pp. 58-59; 66-68)
Chap. 14
(pp.and
274-278)
Climate
Global Change Notes
The Sun - Driving Force for
Climate
10-3
The Sun
•
Introduction
Science quotes of
5th and 6th graders
-
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
Most books now
say our Sun is a
star. But it still
knows how to
change back into a
Sun in the daytime.
Climate and Global Change Notes
The Sun - Driving Force for
Climate
10-4
The Sun (Con’t)
•
•
Medium size star
- Diameter = 1.39 x 10 6 km
(109 times the diameter of Earth)
- Mass = 2.0 x 10 30 kg
(3.3 x 10 5 times the mass of Earth)
QuickTime™ and a
Video decompressor
are needed to see this picture.
Rotation period = average ~27 days
- Variable rotation; Equatorial regions (~25 days)
faster than polar regions (~35 days)
Extreme
uv (30.4 nm)
Image
Climate and Global Change Notes
The Sun - Driving Force for
Climate
The Sun (Con’t)
•
http://sohowww.nascom.nasa.gov/
Coronal Mass Ejection over 8-h period 5-6 August 1999
Average temperature star
-
•
10-5
Interior temperature 15 x 10 6 K
Exterior skin temperature 6000 K
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Interior pressure = 100 x 10 9 times the
surface pressure of the Earth
http://sohowww.nascom.nasa.gov/
X-Ray
Image
QuickTime™ and a
Microsoft Video 1 decompressor
are needed to see this picture.
171 10-10 m
emission
showing the
solar corona at
a temperature
of about 1.3
million K
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Climate and Global Change Notes
The Sun - Driving Force for
Climate
10-6
The Sun (Con’t)
•
Plot of the relative number of stars vs
absolute magnitude shows that fainter
stars (large magnitudes) are much more
numerous than brighter stars
•
The Sun is more luminous than the majority of stars Climate and Global Change Notes
QuickTime™ and a
Video decompressor
are needed to see this picture.
10-7
The Sun - Driving Force for
Climate
Solar Radiation
•
Energy Source
-
•
Nuclear “fusion” of hydrogen to make helium, i.e.,
H2 + H2 => He4
Energy Amount
-
Converts 657 x 106 tons of H2 per s (596 x 109 kg / s)
-
Produces 653 x 106 tons of He2 per s (592 x 109 kg / s)
-
Thus, about 4 x 109 kg / s of mass is converted to energy
Science quotes of
5th and 6th
graders When they broke
open molecules,
they found they
were only stuffed
with atoms. But
when they broke
open atoms, they
found them
stuffed with
explosions.
This is fission.
-
Using Einstein's formula, E = m c2 where E is Energy;
m is Mass; c is Speed of light,3 x 108 m / s. Dividing by time, t, yields
P = E / t = ( m c2 ) / t where P is Power
-
Substituting the values for the Sun yields about P = 3.6 x 1026 watts
>
Note a watt equals a cal / s
Climate and Global Change Notes
10-8
Solar Radiation Variability
Solar Output Variability
•
Sunspots appear as dark spots
where temperatures in the
centers drop to about 3,700 K
•
Sunspots typically last several
days; very large ones may last
for several weeks
•
Sunspots are magnetic regions
with magnetic field strengths
thousands of times stronger
than the Earth's magnetic field
•
Sunspots usually come in
groups
•
Not many sunspots at this
time, but sometimes monthly
average is over a hundred
http://science.msfc.nasa.gov/ssl/
pad/solar/feature1.htm#Sunspots
http://spaceweather.com/
2/25/04
Climate and Global Change Notes
10-9
Solar Radiation Variability
Solar Output Variability
(Con’t)
•
Sunspot number
•
Note 11 year
solar or
sunspot cycle
•
Amount of
energy
emitted by
the Sun is
related to
the sunspot
cycle
http://earthobservatory.nasa.gov/Study/VariableSun/
Climate and Global Change Notes
10-10
Solar Radiation Variability
Solar Output Variability (Con’t)
•
Variations in solar
irradiance at the top
of the Earth’s
atmosphere over the
last 120 years
-
Note 11-year solar
or sunspot cycle
-
Very slight increase
over this 100+
record
Bulletin of American Meteorological
Society, June 2003, p. 743
http://www.doc.mmu.ac.uk/aric/gccsg/2-5-3.html
Climate and Global Change Notes
10-11
The Solar System
Percentage Mass of Components
•
•
To be a planet, an object must meet
three criteria:
Sun: 99.85%
Planets: 0.135%
(1) It must have enough mass and
gravity to gather itself into a ball.
(2) It must orbit the sun.
•
Comets: 0.01% ?
•
Satellites: 0.00005%
•
Minor Planets: 0.0000002% ?
•
Meteoroids: 0.0000001% ?
•
Interplanetary Medium: 0.0000001% ?
•
Jupiter consists of more than twice the matter of all the other planets
combined
(3) It must reign supreme in its own
orbit, having "cleared the
neighborhood" of other competing
bodies.
Climate and Global Change Notes
10-12
The Solar System
Description
•
Sun and
8 planets
and dwarf
planets
(Pluto and
others)
•
Satellites of the planets, numerous comets,
asteroids, meteoroids, and the interplanetary medium
Mercury Earth
Jupiter Saturn
Sun
Venus
Mars
Uranus
http://photojournal.jpl.nasa.gov/
Neptune
Pluto & other
dwarf planets
Climate and Global Change Notes
10-13
The Solar System
10th Planet Discovered??
http://science.nasa.gov/headlines/
y2005/29jul_planetx.htm?list159742
•
29 July 29 2005 - Astronomers discovered a new planet beyond Pluto, about 97
times farther from the Sun than Earth, i.e., 97 Astronomical Units (AU).
•
Scientists working to better estimate its size and its motions. They believe it
is bigger than Pluto
•
Astronomers determine a planets size by measuring its brightness
•
Planets shine by reflecting sunlight
The bigger the planet, generally speaking, the more reflection
The planet's temporary name is 2003 UB313. A permanent name has been
proposed to the International Astronomical Union
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Climate and Global Change Notes
10-14
The Solar System
10th Planet Discovered?? (Con’t)
•
•
August 2006 - International Astronomical Union (IAU) General Assembly in
Prague, stated that to be a planet an object must meet three criteria:
-
it must have enough mass and gravity to gather itself into a ball.
-
it must orbit the sun.
-
it must reign supreme in its own orbit, having "cleared the neighborhood" of
other competing bodies.
Thus, Pluto and 2003 UB313 and several other objects circling the Sun in orbits
similar to Pluto’s were defined as "dwarf planets”
Climate and Global Change Notes
10-15
The Solar System
Planet Plus Pluto Statistical Information
Name
Dist
Radius
Mass
Rot
Sat
Incl
Eccen
Den
Sun
0.
109.
332800.
25.-36.*
9.
-.-
-.-
1.41
Mercury
0.39
0.38
0.05
58.8
0.
7.
0.2056
5.43
Venus
0.72
0.95
0.89
244.
0.
3.394
0.0068
5.25
Earth
1.0
1.00
1.00
1.000
1.
0.000
0.0167
5.52
Mars
1.5
0.53
0.11
1.029
2.
1.850
0.0934
3.95
Jupiter
5.2
11.
318.
0.411
16.
1.308
0.0483
1.33
Saturn
9.5
9.
95.
0.428
18.
2.488
0.0560
0.69
Uranus
19.2
4.
15.
0.748
15.
0.774
0.0461
1.29
Neptune
30.1
4.
17.
0.802
8.
1.774
0.0097
1.64
Pluto
39.5
0.18
0.002
0.267
1.
17.15
0.2482
2.03
Dist = Distance to the Sun in AUs
Mass = Mass in terms of the Earth’s
Sat = Number of associated satellites
Eccen = Orbital eccentricity
Radius = Radius in terms of the Earth’s
Rotate = Rotation rate in Earth days
Incl = Orbital inclination in degrees
Den = Density in g/m3
* Sun’s period of rotation at the surface varies from ~25 days at the equator to 36 days at the
poles. Deep down, below the convective zone, the period of rotation appears to be 27 days.
Climate and Global Change Notes
10-16
Solar Radiation Variability
Solar Radiation Intensity
•
Intensity = energy per unit time per unit area = power per unit area; power
-
Units
> cal / s - m2 or watt / m2
‡ watt = cal / s
Solar Energy the Earth Receives
•
Sun’s energy is emitted in all
directions
•
Intensity of the Sun’s energy decreases as the square of the distance from the
Sun (radius of planet’s orbit) increases, i.e., referred to as the “One Over R 2
Law”
I a 1 / (distance ) 2 or
I a 1 / R2
Climate and Global Change Notes
10-17
Solar Radiation Variability
Solar Energy the Earth Receives (Con’t)
•
The Earth intercepts only a small portion of the Sun’s energy; about
1.62 x 10 17 watts
•
Solar power the Earth receives adds up to 18,000 times more energy than
humankind consumes as fuel and commercial energy
Climate and Global Change Notes
10-18
Solar Radiation Variability
Solar Energy the Planets Receive
Name
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Dist (m)
5.85 X 10 10
1.08 X 10 11
1.50 X 10 11
2.25 X 10 11
7.80 X 10 11
1.43 X 10 12
2.88 X 10 12
4.52 X 10 12
5.93 X 10 12
Radius (m)
2.42 X 10 6
6.05 X 10 6
6.37 X 10 6
3.38 X 10 6
7.01 X 10 7
5.73 X 10 7
2.55 X 10 7
2.55 X 10 7
1.15 X 10 6
Energy Received*
(watts)
1.54 X 10 17
2.83 X 10 17
1.62 X 10 17
2.03 X 10 16
7.26 X 10 17
1.46 X 10 17
7.04 X 10 15
2.87 X 10 15
3.37 X 10 15
Dist = Distance to the Sun
Radius = Planet’s radius
Energy Received = Energy received from the Sun
• Calculations based on numbers from the class laboratory exercise. More precise numbers will yield
slightly different results.
Mercury Earth
Jupiter Saturn
Sun
Venus
Mars
Uranus
Neptune
Pluto
Climate and Global Change Notes
10-19
Solar Radiation Variability
Radiation Balance Assumption
Name
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
Temp (K)
438.
322.
274.
223.
120.
89.
62.
50.
44.
Temp with
Albedo (K)
228. (75%)
250. (30%)
215. (15%)
Incoming
Solar
Radiation
Solid
Planet
Outgoing
Radiation
Temp = Planet’s average temperature assuming planet is a solid globe with no
atmosphere and no albedo
Temp with Albedo = Planet’s average temperature assuming planet is a solid globe with no
atmosphere, but with an albedo
Climate and Global Change Notes
10-20
Solar Radiation Variability
Solar Angle and Intensity
•
•
Area of a flashlight beam spreads over a larger area as the flashlight moves
from directly overhead to a more glancing angle
Intensity decreases as the angle between the light’s rays and the surface
decreases
Directly Overhead
Glancing Angle
Side View
Overhead View
Climate and Global Change Notes
10-21
Solar Radiation Variability
Solar Angle and Intensity (Con’t)
•
Global variability
-
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Tilt of axis effect on
solar intensity
http://svs.gsfc.nasa.gov/vis/a000000/a000000/a000077/index.html
Climate and Global Change Notes
10-22
Solar Radiation Variability
Solar Angle and Intensity (Con’t)
•
Intensity
decreases
as the angle
between the
Sun's rays and
the Earth's
surface
decreases
>
Axis of
Rotation
Glancing Angle
Directly Overhead
Angle
increases
as move
away from
tropics
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Climate and Global Change Notes
10-23
Solar Radiation Variability
Solar Angle and Intensity (Con’t)
•
Intensity
decreases
as the depth
of atmosphere
penetrated
increases
Axis of Rotation
Solar
Rays
Penetration
QuickTime™ and a
Depth
TIFF (Uncompressed) decompressor
are needed to see this picture.
Solar
Rays
Penetration
Depth
Atmospheric Layer
Climate and Global Change Notes
10-24
Solar Radiation Variability
•
Global variability
2)
•
-
Radiation Intensity ( W / m
Solar Angle and Intensity (Con’t)
Spherical shape
of the Earth
400
300
200
100
90N
Local variability
-
Solar Radiation
Intensity Received
50N
30N
10N 0
10S
30S
50S
90S
Latitude
Mountains
>
Southside for wine in NY
>
North side for ski slopes in NY
Climate and Global Change Notes
10-25
Solar Radiation Variability
Earth’s Orbit
•
Note: Orbit is elliptical;
it has an eccentricity
September 23
December 22
Perihelion
About
January 3
Sun
152 x 106 km
Aphelion
About
July 4
June 22
147 x 106 km
March 21
Climate and Global Change Notes
10-26
Solar Radiation Variability
Seasons
•
Caused by the tilt of the Earth's axis with
respect to the plane of the Earth's orbit
-
Changes both the angle between
the Sun's rays and the Earth's surface
and the depth of atmospheric penetration
-
Changes the length of daylight
-
Example: December solstice
(Northern Hemisphere Winter
solstice)
Factoids A planet’s rotation and tilt
are result of collisions.
Uranus axis is tilted 90°.
Venus rotates east to west
instead of west to east like
the Earth.
Climate and Global Change Notes
10-27
Solar Radiation Variability
Seasons (Con’t)
•
Earth’s annual
trip around the
Sun
http://svs.gsfc.nasa.gov/vis/a000000/a000000/a000077/index.html
Climate and Global Change Notes
10-28
Solar Radiation Variability
Seasons (Con’t)
•
Satellite view looking
down on the North
Pole
Climate and Global Change Notes
10-29
Solar Radiation Variability
Seasons (Con’t)
•
Satellite view looking up
at the South Pole
Climate and Global Change Notes
10-30
Solar Radiation Variability
Universal Time
d
2006
Perihelion Jan 4
Aphelion Jul 3
h
d
h m
d
h m
15
23
Equinoxes
Solstices
Mar 20 18 26
Jun 21 12 26
Sep 23 04 03
Dec 22 00 22
2007
Perihelion Jan 3
Aphelion Jul 7
20
00
Equinoxes
Solstices
Mar 21 00 07
Jun 21 18 06
Sep 23 09 51
Dec 22 06 08
2008
Perihelion Jan 3
Aphelion Jul 4
00
08
Equinoxes
Solstices
Mar 20 5 48
Jun 20 23 59
Sep 22 15 44
Dec 21 12 04
2009
Perihelion Jan 4
Aphelion Jul 4
15
02
Equinoxes
Solstices
Mar 20 11 44
Jun 21 5 45
Sep 22 21 18
Dec 21 17 47
2010
Perihelion Jan 3
Aphelion Jul 6
00
11
Equinoxes
Solstices
Mar 20 17 32
Jun 21 11 28
Sep 23 03 09
Dec 21 23 38
2011
Perihelion Jan 3
Aphelion Jul 4
19
15
Equinoxes
Solstices
Mar 20 23 21
Jun 21 17 16
Sep 23 09 04
Dec 22 05 30
http://aa.usno.navy.mil/data/docs/EarthSeasons.html
Climate and Global Change Notes
10-31
Solar Radiation Variability
Seasons (Con’t)
•
View of Earth from the Sun throughout the year
•
North and South poles are denoted by
June Solstice
June 21-22
Sun Vertical
at Latitude 23.5°N
September Equinox
September 21-22
Sun Vertical
at Latitude 0°
December Solstice
December 21-22
Sun Vertical
at Latitude 23.5°S
March Equinox
March 21-22
Sun Vertical
at Latitude 0°
Climate and Global Change Notes
10-32
Solar Radiation Variability
Seasons (Con’t)
•
Earth year animation from the Sun’s point of view
Climate and Global Change Notes
Global Radiation Budget
Variations
Seasons (Con’t)
Summer - 6/21 23:00 UTC
10-33
http://www.fourmilab.ch/cgi-bin/Earth
From 0°
Winter - 12/21 23:00 UTC
Sun’s Rays
Circle of illumination
Climate and Global Change Notes
Global Radiation Budget
Variations
Seasons (Con’t)
Summer - 6/21 23:00 UTC
10-34
http://www.fourmilab.ch/cgi-bin/Earth
From 45°S
Arctic Circle
Winter - 12/21 23:00 UTC
Climate and Global Change Notes
10-35
Solar Radiation Variability
Special Latitudes
•
Based on the Sun’s angle with the Earth’s surface
NP
Arctic Circle
23.5°
Tropic of Cancer
66.5°N
Equator
23.5°N
Tropic of Capricorn
Antarctic Circle
0°
23.5°S
66.5°S
Axis of Rotation
Climate and Global Change Notes
10-36
Solar Radiation Variability
Seasons (Con’t)
•
Antarctic Daylight
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Climate and Global Change Notes
10-37
Solar Radiation Variability
Solstice Shadows at Local Noon
June 21, '02
Where
Length of shadow
Your height
North Pole (90°N)
2.3
Los Angeles (34°N)
0.19
Huntsville (34°N)
0.19
New York (41°N)
0.31
Buenos Aires (34°S)
1.6
Johannesburg (26°S) 1.2
South Pole (90°S) no shadow
Dec. 22, '02
Shaq's (7’ 1”) Shadow
Length of shadow
Max - Min (ft, in)
Your height
no shadow
16' 4"
1.6
1' 4” - 11' 4
1.6
1' 4” - 11' 4
2.1
2' 2” - 14' 11"
0.19
1' 4” - 11' 4"
0.05
0' 4” - 8' 5”
2.3
16' 4"
The ratio of your height and the length of your shadow at local noon on Jun 21st
and Dec 22nd. To calculate how long your shadow would be on the first day of
summer in N.Y., multiply your height by 0.31 -- the ratio listed for N.Y. on Jun 21.
Length of shadow = Your height * tan (90° - Sun elevation @ local noon)
Sun elevation @ local noon = 90° - (Location’s latitude ± 23.5°)
where you use - if Sun is in your hemisphere and + if sun in alternate hemisphere
Climate and Global Change Notes
10-38
Global Radiation Budget
Variations
Seasons (Con’t)
Solar Parameters for:
•
•
•
•
Huntsville, AL
(Latitude: 34.4°N)
June Solstice (Northern Hemisphere Summer)
Maximum solar altitude angle:
79.1°
Longest day:
14.5 hours
Shortest night:
9.5 hours
Philadelphia, PA
(Latitude: 40.0°N)
73.5°
15 hours
9 hours
September Equinox (Northern Hemisphere Fall)
Solar altitude angle:
55.6°
Day:
12 hours
Night:
12 hours
50.0°
12 hours
12 hours
December Solstice (Northern Hemisphere Winter)
Minimum solar altitude angle:
32.1°
Shortest day:
9.5 hours
Longest night:
14.5 hours
26.5°
9 hours
15 hours
March Equinox (Northern Hemisphere Spring)
Solar altitude angle:
55.6°
Day:
12 hours
Night:
12 hours
50.0°
12 hours
12 hours
Climate and Global Change Notes
Global Radiation Budget
Variations
10-39
Seasons (Con’t)
All's Right With The World
by Robert Browning (1812 - 1889)
The years at the spring
The day's at the morn
Morning's at seven
The hill-side's dew-pearled
The lark's on the wing
The snail's on the throne
God's in his heaven...
All's right with the world!
Great poem but does the science seem correct?
Climate and Global Change Notes
10-40
Solar Radiation Variability
Seasons (Con’t)
Science quotes of 5th and 6th graders -
•
South America has cold summers and hot
Insolation
-
Incoming solar radiation
Solar energy per unit area
at the Earth’s surface
•
Same as solar energy intensity
•
Annual variation
•
Note: Southern Hemisphere receives
more radiation during its summer
(January) than does the Northern
Hemisphere during its summer (July)
-
winters, but somehow they still manage.
QuickTime™ and a
TIFF (Uncom pressed) decomp ressor
are n eeded to see this picture.
Remember Earth is closer to the
Sun in July than January
Climate and Global Change Notes
10-41
Milankovitch Cycles
Earth’s Orbit
•
Orbit changes with time in three
ways
Milankovitch
(Serbian astronomer)
1943
http://www.ngdc.noaa.gov/paleo/sli
des/images/base/iceage11.gif
Eccentricity
•
Defined as e = (a2 - b2)1/2 / a
where a is the semi-major axis
and b is the semi-minor axis
http://earthobservatory.nasa.gov/
Library/Giants/Milankovitch/
milankovitch.html
b
a
Earth
•
Sun
Currently e = 0.0167
http://earthobservatory.nasa.gov/Library/
Giants/Milankovitch/milankovitch_2.html
Climate and Global Change Notes
10-42
Milankovitch Cycles
Eccentricity (Con’t)
•
Jupiter’s gravitational force results in Earth’s orbit varying from nearly circular
with eccentricity near 0.0 to about 0.06
http://www.museum.state.il.us/exhibits/
ice_ages/eccentricity_graph.html
413,000 years
100,000 years
Eccentricity of the Earth's orbit
over the last 750,000 years
Blue line traces the eccentricity
of the elliptical orbit as it varies
from circular (0.0); red line
shows today's value for
comparison.
Berger and Loutre (1991)
•
Current difference in distance to the Sun at perihelion and aphelion is 3-4%
•
Period - Dominate period of 413,000 and minor period of 100,000 years
Climate and Global Change Notes
10-43
Milankovitch Cycles
Obliquity
•
Change in the tilt of the Earth's axis
•
Period — 41,000 years
•
Changes between ~22.1° and ~24.5°
-
•
Current tilt of axis is 23.5° but
23.5° tilt varies from 22.1° to 24.5°
Orbital Plane
Sun
Moon helps stabilize the obliquity;
without the Moon this variation in the tilt
could range much larger. The obliquity
angle could reach 85°
Less tilt implies
-
More snow at poles because more
moisture
-
Cooler summers, thus less snow melt
-
Therefore, good
conditions for
initiation of glaciers
http://earthobservatory.
nasa.gov/Library/Giants
/Milankovitch/milankovit
ch_2.html
Climate and Global Change Notes
10-44
Milankovitch Cycles
Obliquity
•
Variation in the tilt of the Earth's axis over the last 750,000 years
Blue line traces the
tilt in degrees; red
line shows today's
value for
comparison
Berger and Loutre
(1991)
http://www.museum.state.il.us/exhibits/ice_ages/tilt_graph.html
Climate and Global Change Notes
10-45
Milankovitch Cycles
Obliquity (Con’t)
•
Change in Ice for past 21,000 years (1/2 period)
•
Matches change in obliquity from 22.1° to 23.5°
http://geochange.er.usgs.gov/pub
/sea_level/Core/raw/quaternary/
images/gif/ice_age.gif
Climate and Global Change Notes
10-46
Milankovitch Cycles
Precession
•
Wobble in the tilt of the Earth's axis
•
Period — 22,000 years
•
Like spinning top
•
Changes hemispheric climate
not whole Earth
QuickTime™ and a
Sorenson Video 3 decompressor
are needed to see this picture.
http://earthobservatory.nasa.gov/Library/Giants/
Milankovitch/milankovitch_2.html
Planetary axes would not precess or change obliquity if the planets were perfect
spheres. However planetary rotation causes the equators to bulge. This gives a
“handle” that the gravity of the other planets “grabs onto”, and twists the planetary
spin. This causes precession and obliquity changes.
Climate and Global Change Notes
10-47
Milankovitch Cycles
Precession (Con’t)
•
Precession of the equinox over the last 750,000 years
Blue line traces the
precession; red line
shows today's
value
Berger and Loutre
(1991)
http://www.museum.state.il.us/exhibits/ice_ages/precession_graph.html
Climate and Global Change Notes
10-48
Milankovitch Cycles
Precession (Con’t)
•
September
Current
December
Sun
June
March
September
•
11,000 years from now
December
Sun
June
March
Climate and Global Change Notes
10-49
Milankovitch Cycles
Precession (Con’t)
•
Stars that Earth’s axis of rotation
point as the axis precesses
•
Note this means the pole star
changes with time
•
Currently Earth’s axis points
toward “Polaris”
Past, Present & Future Pole Stars
Year
c. 3,000BC
c. 1,000BC
Present
c. 4,000AD
c. 7,500AD
c. 14,000AD
Constellation
Draco
Usra Minor
Usra Minor
Cassiopeia
Cepheus
Lyra
Closest Star
Thuban
Kochab
Polaris
Alrai
Aldera min
Vega
http://inkido.indiana.edu/a100/celestialsphere2.html
Climate and Global Change Notes
10-50
Milankovitch Cycles
Precession (Con’t)
•
http://www.ukexpert.co.uk/photopost/
data/588/7the-pyramids.jpg
Dating the Pyramids
-
Egyptian pyramids at Giza were built roughly
4,500 years ago. How do we know?
>
By determining how long each individual
Pharaoh held power, adding all the years and working backwards
‡ Not very accurate
>
Carbon dating
‡ Provides dates for the pyramids plus or minus 100 years
>
Astronomical dating
The Ancient Egyptians aligned the sides of their pyramids to the points of the
compass, with extraordinary accuracy. The most accurate is the Pyramid of Khufu,
called the Great Pyramid. The east and west sides miss True North by less than
three minutes of arc (roughly one tenth the diameter of the full moon). It took over
4,000 years before the astronomer, Tycho Brahe, was able to take astronomical
measurements to a greater accuracy.
Climate and Global Change Notes
10-51
Milankovitch Cycles
Precession (Con’t)
•
How did they manage to align the sides so accurately with the North Pole?
Look at the time lapse photograph of stars over
a full night. Note all the visible stars appear to
move in circles (some big and some small).
Today the star Polaris (The North Star or Pole
Star) makes a very small circle indicating that
it’s very near the Celestial North Pole.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Because of precession, the Earth’s axis of
rotation is slowly sweeping out a great circle,
pointing to different parts of the sky. In the years when the pyramids were being
built, two stars, Mizar (Eta-Ursae Majoris) in the Big Dipper and Kochab (Beta-Ursae
Minoris) in the Little Dipper, appeared to rotate around the Celestial North Pole.
Star trails as the United Kingdom Infrared Telescope (UKIRT) watches the night sky. CREDIT:
Nik Szymanek. http://outreach.jach.hawaii.edu/pressroom/2003-estar/ukirtnight-small.jpg
Climate and Global Change Notes
10-52
Milankovitch Cycles
Precession (Con’t)
Precession is actually an advantage for dating the
pyramids. If you use the method outlined to the right
before 2,467 BC, your line would be slightly to the west
of True North and after that date you'd be to the east of
True North. The Pyramids of Giza show exactly this
relationship - the earlier ones are aligned slightly to the
west, and the later ones slightly to the east.
Using this method, dates of when the pyramids were built
have been calculated to within five years or so.
In 2,467 BC, it would have
been quite easy to find
True North. You'd have to
build some scaffolding, and
hang a string with a heavy
weight. This would hang
perfectly vertically, pointing
to the center of the Earth.
Then you'd wait until Mizar
and Kochab were vertically
aligned exactly with your
hanging string. Then a line
from you, to the hanging
string, would point due
north to the horizon.
http://www.abc.net.au/science/k2/moments/s221162.htm
Climate and Global Change Notes
10-53
Milankovitch Cycles
Periods of Change (Con’t)
Climate and Global Change Notes
10-54
Milankovitch Cycles
Periods of Change (Con’t)
•
Resulting change
Climate and Global Change Notes
10-55
Milankovitch Cycles
65°N Insolation and Glacial Cycles
•
Milankovitch theory suggests Earth
orbital changes result in the
observed 100 kyr cycle in ice ages
•
Gray bars indicate interglacial
periods, defined here as deviations
in 5 kyr average of at least 0.8
standard deviations above mean
•
Data Quinn et al. (1991),
Jonathan Levine's insolation
calculator and Lisiecki and
Raymo (2005)
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
http://en.wikipedia.org/wiki/Image:Milankovitch_Variations.png
This image
was produced by Dragons flight from publicly available
.
data, and is released under the GFDL
Lisiecki, L. E., and M. E. Raymo, 2005: A Pliocene-Pleistocene stack of 57 globally distributed benthic d18O
records. Paleoceanography, 20.
Quinn, T.R. et al., 1991: A three million year integration of the Earth's orbit. The Astronomical Journal, 101,
2287-2305.
Climate and Global Change Notes
10-56
Milankovitch Cycles
Temperature and Ice Ages
•
Comparison of Antarctic
ice core temperature
changes to changes in
global ice volume
•
Note they are highly
correlated
•
Red horizontal lines
indicate modern
temperatures and ice
volume
•
Note Antarctic temperature
http://en.wikipedia.org/wiki/Image:Ice_Age_Temperature.png
This image was produced by Dragons flight from publicly available
records show that the present
data, and is released under the GFDL
interglacial seems to be relatively
cool compared to previous interglacials
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Climate and Global Change Notes
10-57
Solar Radiation Variability
Earth’s Annual Temperature Cycle at 900 m b 1 km / 3,300
ft
Red = 20 Year Average
Yellow = 2003 Data
Green = 2004 Data
Short Yellow = 2005 Data
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
http://pm-esip.nsstc.nasa.gov/
Climate and Global Change Notes