April 13 - 27, 2005 April 13 - 27, 2005 eviews will be handed back Thurs/Fri to eviews will be handed back Thurs/Fri to es, fax, etc. es, fax, etc. s handed back next week. s handed back next week. ng for periods and patterns in climate recor ng for periods and patterns in climate recor try of Earth’s orbit try of Earth’s orbit nomical control of solar radiation nomical control of solar radiation ds and patterns as chronometers ds and patterns as chronometers nomical control of monsoons, ice sheets, nomical control of monsoons, ice sheets, iño, GHGs iño, GHGs ores as climate recorders ores as climate recorders
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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.
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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