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April 13 - 27, 2005. NOTE: Reviews will be handed back Thurs/Fri to mailboxes, fax, etc. Midterms handed back next week. Searching for periods and patterns in climate records: Geometry of Earth’s orbit Astronomical control of solar radiation Periods and patterns as chronometers - PowerPoint PPT Presentation
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April 13 - 27, 2005April 13 - 27, 2005
NOTE: Reviews will be handed back Thurs/Fri toNOTE: Reviews will be handed back Thurs/Fri tomailboxes, fax, etc.mailboxes, fax, etc.Midterms handed back next week.Midterms handed back next week.
Searching for periods and patterns in climate records:Searching for periods and patterns in climate records:• Geometry of Earth’s orbitGeometry of Earth’s orbit• Astronomical control of solar radiationAstronomical control of solar radiation• Periods and patterns as chronometersPeriods and patterns as chronometers• Astronomical control of monsoons, ice sheets, Astronomical control of monsoons, ice sheets, El Niño, GHGsEl Niño, GHGs• Ice cores as climate recordersIce cores as climate recorders
In addition to long-term trends, Zachos found regularly-spaced warm-cold alternations
Ultimately named “Milankovitch cycles” after Milutin Milankovitch,Serbian mathematician (1879 - 1958).
Developed mathematical theory of Earth’s ice ages based onamount of sunlight Earth receives (published in 1920).
After Raymo, M.E., Ann. Rev. Earth Plan. Sci. 22, 353-383, 1994
View of Sun and Earth from above the North Pole
day nightN
Eccentricity and the shape of Earth’s Orbit
Earth’s currently 0.017 --> nearly circularMaximum = 0.06
2a = major axis
2b = minor axisempty focus
E
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-6
Eccentricity and the shape of Earth’s Orbit
empty focus
rr*
r + r* = 2a
EPerihelion
Aphelion
E
E
What happens to the solar flux at perihelion and aphelion?Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-6
Where are Northern Hemisphere Summer and Winter located?
Shape of Earth’s Orbit Today
Equinox: length ofnight and day are equal.
Solstice: longest andshortest days of the yearRuddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-2
Milutin Milankovitch
Calculated the changes in Earth’s orbital parameters during the past.
= 0.005
Presently = 0.0167
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-7
All of the Planets in the Solar System are pulling on Earth
E V
M
J
S
EV
M
J
S
All of the Planets in the Solar System are pulling on Earth
Sun’s equator
Mercury VenusEarth Mars
Jupiter
Ecliptic
Earth is not “straight up and down” with respect to the ecliptic.
Obliquity and the Eclipitc
Obliquity- Earth’s tilted rotation axis
No tilt --> No seasons
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-3a
Obliquity- Earth’s tilted rotation axis
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-1
Obliquity- Earth’s tilted rotation axis
Northern Hemisphere Winter:• occurs at perihelion• tilted AWAY from Sun• winter radiation higher than for circular orbit
Southern Hemisphere Summer:• occurs at perihelion• tilted TOWARDS Sun• summer radiation higher than for circular orbit
At present
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-5
Obliquity- Earth’s tilted rotation axis
Northern Hemisphere Summer:• occurs at aphelion• tilted towards Sun• summer radiation lower than for circular orbit
Southern Hemisphere Winter:• occurs at aphelion• tilted away from Sun• winter radiation lower than for circular orbit
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-5
Obliquity- Earth’s tilted rotation axis
Northern Hemisphere Summer:• occurs at aphelion• tilted towards Sun• summer radiation lower than for circular orbit
Northern Hemisphere Winter:• occurs at perihelion• tilted AWAY from Sun• winter radiation higher than for circular orbit
At present, northern summers and winters are both milderthan they could be. Low seasonal contrast.
At present Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-13
Obliquity- Earth’s tilted rotation axis
At present, southern summers and winters are both extreme.High seasonal contrast.
Southern Hemisphere Summer:• occurs at perihelion• tilted TOWARDS Sun• summer radiation higher than for circular orbit
Southern Hemisphere Winter:• occurs at aphelion• tilted away from Sun• winter radiation lower than for circular orbit
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-13
Obliquity- Earth’s tilted rotation axis
Earth’s obliquity varies from ~22 to 24.5˚with a period of 41,000 years.
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-4
Wobble- Precession of Earth’s rotation axis
Wobble = DIRECTION in which spin axis leans
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-8
Wobble- Precession of Earth’s rotation axisEarth’s rotation axis sweeps out a circle every 27,500 years.• Right now, axis points at Polaris (North Star)• ~2000 B.C.. Alphas Draconis was pole star• ~ 14,000 A.D. Vega will be pole star
en.wikipedia.org
Appearsclockwisewhen viewedfrom abovenorth pole.Appears counter-clockwisewhen startsviewedfrom Earth.
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-9
Precession of Earth’s orbit
Elliptical shape of Earth’s orbit is rotating,
Precession of Earth’s orbit
Elliptical shape of Earth’s orbit is rotating
Precession of Earth’s orbit
Elliptical shape of Earth’s orbit is rotating
Appears counter-clockwise when viewed from above Earth’sNorth pole
Precession of Earth’s orbit
Elliptical shape of Earth’s orbit is rotating
Wobble and precession of ellipse IN OPPOSITE DIRECTIONS.Combined effect: 23,000 years to make a full cycle.
Appearsclockwisewhen viewedfrom aboveNorth pole
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-9
Equinoxes and solstices move around the ellipse
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-2
Effect of Precession on sunlight received
0.5 Myr0.5 Myr
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-14
Today
Half a precessional cycle in the past
• Summer at perihelion • LOTS of solar radiation
• Winter at aphelion• Minimal solar radiation
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-13
Insolation changes with latitude AND season through time
Ruddiman, W.F., “Earth’s Climate, Past and Future,” W.H. Freeman, 2001, Fig. 8-16
Inco
min
g F
lux
W/m
2
Calendar Year AD
1.3 W/m2
0.1 %
Redrawn from Frolich and Lean, 1998
Does all this affect Earth’s climate?
Critics said: effect exceeds the cause.
Data to support Milankovitch was a long time coming
Oscillations every100,000 years
Oscillations every23,000 and 41,000 years
After Raymo, M.E., Ann. Rev. Earth Plan. Sci. 22, 353-383, 1994
150
200
250
300
350
400
0 100000 200000 300000 400000
Age (yr BP)
1960 - 2000 AD
450,000 year record of CO2 from Vostok Ice Core, Antarctica
Data generously made available online by the Vostok Ice Core group,
N
R
R
N
Normal Reverse
Orbital Tuning-- what do you think?
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20
10
0
Meters below seafloor (
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mbsf
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)
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2
4
6
8
12
14
16
18
1 0 -123
δ18
O
1st reversal = 780,000 yr B.P.
top = 0 yr
] = ~ 90 - 115,000 years apart
Orbital Tuning-- what do you think?
Orbital tuning:1. Apply magnetostratigraphy2. Assign wiggles to be spaced 100,000 years3. Match peaks and troughs to insolation curve
Orbital Tuning in the Vostok ice core
Generously made available online at http://www.usgcrp.gov/usgcrp/images/Vostok.jpg