Astronomical Control of Solar Radiation By Jessica Juday Lyudmila Koba Luke Mros Grant Prehn and Vincent Xu Earth spins on its axis Makes 1 complete revolution every 24hrs Earths axis is tilted at 235 ID: 211306
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Slide1
Chapter 7
Astronomical Control of Solar Radiation
By: Jessica Juday, Lyudmila Koba, Luke Mros, Grant Prehn and Vincent XuSlide2
Earth spins on its axis
Makes 1 complete revolution every 24hrs
Earth’s axis is tilted at 23.5°
Earth’s tilt referred to as it’s “obliquity”
Earth’s Tilted Axis of Rotation and the SeasonsSlide3
Earths Rotation Around the Sun
1 revolution around the Sun = 365 days
Earth’s tilt
combined with solar orbit gives us seasons
Seasons accumulate at Solstices
Summer Solstice - longest day
Winter Solstice - shortest day
Northern Hemisphere:
Summer Solstice Jun 21
st
Winter Solstice Dec 21
st
Southern Hemisphere:
Summer Solstice Dec 21
st
Winter Solstice Jun 21
st
(reverse from that of the north)Slide4
Earths Tilt and it’s Direction Are Constant Through
out OrbitReason why we have regular seasons
Earths tilt defines the Arctic Circles at 66.5°
During Winter Solstice, no direct sunlight reaches poleward of this latitude Slide5
At Winter Solstice, no direct sunlight
reaches
past this point Slide6
Equinoxes occur midway between solstices.
Direction of Earth’s tilt not pointing towards/away from the sun.
Days/Nights become equal in length
EquinoxesSlide7
Earths orbit is “
Elliptical”
Orbital eccentricity is due to gravitational pull on Earth from other planets
Earth’s distance from the Sun varies due to position in elliptical orbitClose pass: “
Perihelion”
Distant pass: “
Aphelion
”
Earths Eccentric OrbitSlide8
Close pass: “
Perihelion”
146 million km
Jan 3rd
Distant pass: “
Aphelion
”
152 million km
Jul 4
th
7 days longer between equinoxes
3% variation in distance
Slight changes in radiation received
Small effect on seasonsSlide9Slide10
Long-Term Changes
in Earth’s Orbit
Orbit varies due to gravitational attractions between Earth and other Celestial bodies
Causes variation in Earth’s angle of tilt, eccentricity of orbit and positions of solstices/equinoxes in the orbit
These variations are Cyclical…Slide11
Changes like Earth’s orbit and amount of radiation received occur in cycles.
We express these cycles as “Wavelengths
”
Cycles and Modulation…Slide12
Period
A wavelength expressed in units of time
Frequency
# of cycles that occur in 1 Earth year
AmplitudeMeasure of deviation from long-term averageSlide13
Modulation
Amplitude of peaks and valleys change in a cyclic way
Modulation of a cycle is not in itself a cycle!Slide14
If the Earth had a circular orbit with no tilt to the axis, we would have no seasons for there would be no change in solar radiation.
Extremes of TiltSlide15
Alternately, if Earth’s axis had a tilt of 90 degrees, the poles would alternate between day-long darkness, and day-long direct overhead sunshine.
Extremes of TiltEquator
90 degree tiltSlide16
Decreased axis tilt diminishes the difference in seasons and brings it closer to that of the example below.
Decreasing TiltsSlide17
Increased tilt of the axis results in more solar radiation at the summer season poles, and less to the winter season poles.
Effects on Polar RegionsSlide18
This can be described by reference to the major (longer) and minor (shorter) axis.The degree of departure from a circular orbit can be described by this equation.
The Shape of an EllipseE = Eccentricity
a and b = ½ the lengths of major and minorSlide19
The eccentricity of an ellipse is related to half of the lengths of it’s longer and shorter axesSlide20
Changes in Earth’s Orbit Through TimeThe earth’s orbit used to be more elliptical or “eccentric” than it is today.
There is orbital variation at periods of 413,000 years, and 100,000 years.Slide21
The longer cycle of 413,000 is not as noticeable because it appears in between the 100,000 year cycles between large and small peaks.Larger amplitudes appear at 200,000 yrs, 600,000 yrs, and 1,000,000 yrs.A third cycle happens at 2.1 million years, but it is weak in amplitude.
Eccentricity CyclesSlide22
Precession
What is it? -The motion of the axis of a spinning body, such as the wobble of
a spinning top,when an external force
acting on the axis.Slide23
Earths Three Forms of PrecessionPrecession of the Axis
Precession of the EllipsePrecession of the Solstices and the EquinoxesSlide24
1. Precession of the Earths Axis
-One rotation every 25,000 years-Caused by the gravitational pull on the earth's equatorial bulgeSlide25Slide26
-Causes the Celestial northern star to vary-Bright star at the bottom is the star VegaSlide27
Axial Precession CycleSlide28
- The ellipse of the earth’s orbit also hasa precession-Rate of precession is even slower than
that of the axial precession ~22,000 yearshttp://www.youtube.com/watch?v=82p-DYgGFjI&list=PL1Iewcbx3MoVFpQmNOgSy1cu8LeNZUegN2. Precession of the EllipseSlide29
3. Precession of the Equinoxes- The point where the equinoxes and solstices occur has a precession of it’s own.
Why is it important?-the point at which the solstices and equinoxes occur determines the intensity of the seasonsWhat is it caused by?-the combination of the precession of the axis and the ellipse.Slide30
One full rotation take between 19-23 Thousand years
What does it look like?Slide31Slide32
Insolation Changes by Month and SeasonLong-term changes in tilt
Long-term changes in precessionSlide33
June and December insolation variations
Precession at low and middle latitudeseffects of tilt evident only at higher latitudesSlide34
Phasing of insolation maxima and minimaDifference between North Pole and South PoleSlide35
Insolation Changes by Caloric SeasonsFamily of monthly precession curves
Caloric insolation seasonsSlide36
Caloric season insolation anomaliesSlide37
Complication from overlapping cyclesSearching for Orbital-scale Changes in Climatic RecordsSlide38
Time Series Analysis
Time Series AnalysisA method used to analyze climate record data, in hopes to extract rhythmic cycles.References patterns against a time component.
Spectral Analysis
Referencing sine waves with climate data to measure their correlation.A strong correlation indicates a strong cycle.
Power Spectrumthe result of a spectrum analysisUsed to show data.
prone to interference from equipment and climate irregularities.
Filtering
A method of honing in on a specific set of data to better analyze it without referencing other data.Slide39Slide40
Effects of Undersampling Climate Records
Time series analysis requires multiple cycle sightings to be accurate (>4).AliasingFalse trends found by way of undersampling.
Combated with frequent readings and large sample sizes.
False trends tend to only measure part of natural cycles. This causes skewed results.Slide41
Tectonic-Scale Changes in Earth’s Orbit
Earth’s characteristics are not set in stone and are prone to change over time.Coral studies from 440 million years ago.11% more tidal cycles per year.
Earth spun 11% more on its rotational axis.
Not everything in earth is a cycle we can see.