Presentation on theme: "Astronomical Control of Solar Radiation"— Presentation transcript:
1 Astronomical Control of Solar Radiation Chapter 7Astronomical Control of Solar RadiationBy: Jessica Juday, Lyudmila Koba, Luke Mros, Grant Prehn and Vincent Xu
2 Earth’s Tilted Axis of Rotation and the Seasons Earth spins on its axisMakes 1 complete revolution every 24hrsEarth’s axis is tilted at 23.5°Earth’s tilt referred to as it’s “obliquity”
3 Earths Rotation Around the Sun 1 revolution around the Sun = 365 daysEarth’s tilt combined with solar orbit gives us seasonsSeasons accumulate at SolsticesSummer Solstice - longest dayWinter Solstice - shortest dayNorthern Hemisphere:Summer Solstice Jun 21stWinter Solstice Dec 21stSouthern Hemisphere:Summer Solstice Dec 21stWinter Solstice Jun 21st(reverse from that of the north)
4 Earths Tilt and it’s Direction Are Constant Throughout Orbit Reason why we have regular seasonsEarths tilt defines the Arctic Circles at 66.5°During Winter Solstice, no direct sunlight reaches poleward of this latitude
5 At Winter Solstice, no direct sunlight reaches past this point
6 Equinoxes Equinoxes occur midway between solstices. Direction of Earth’s tilt not pointing towards/away from the sun.Days/Nights become equal in length
7 Earths Eccentric Orbit Earths orbit is “Elliptical”Orbital eccentricity is due to gravitational pull on Earth from other planetsEarth’s distance from the Sun varies due to position in elliptical orbitClose pass: “Perihelion”Distant pass: “Aphelion”
8 Close pass: “Perihelion” Distant pass: “Aphelion” 146 million kmJan 3rdDistant pass: “Aphelion”152 million kmJul 4th7 days longer between equinoxes3% variation in distanceSlight changes in radiation receivedSmall effect on seasons
10 Long-Term Changes in Earth’s Orbit Orbit varies due to gravitational attractions between Earth and other Celestial bodiesCauses variation in Earth’s angle of tilt, eccentricity of orbit and positions of solstices/equinoxes in the orbitThese variations are Cyclical…
11 Cycles and Modulation… Changes like Earth’s orbit and amount of radiation received occur in cycles.We express these cycles as “Wavelengths”
12 Period Frequency Amplitude A wavelength expressed in units of time # of cycles that occur in 1 Earth yearAmplitudeMeasure of deviation from long-term average
13 Modulation Amplitude of peaks and valleys change in a cyclic way Modulation of a cycle is not in itself a cycle!
14 Extremes of TiltIf 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.No Tilt
15 Extremes of TiltAlternately, if Earth’s axis had a tilt of 90 degrees, the poles would alternate between day-long darkness, and day-long direct overhead sunshine.Equator90 degree tilt
16 Decreasing TiltsDecreased axis tilt diminishes the difference in seasons and brings it closer to that of the example below.
17 Effects on Polar Regions Increased tilt of the axis results in more solar radiation at the summer season poles, and less to the winter season poles.
18 a and b = ½ the lengths of major and minor The Shape of an EllipseThis 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.E = Eccentricitya and b = ½ the lengths of major and minor
19 The eccentricity of an ellipse is related to half of the lengths of it’s longer and shorter axes
20 Changes in Earth’s Orbit Through Time The 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.
21 Eccentricity CyclesThe 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.
22 Precession What is it? -The motion of the axis of a spinning body, such as the wobble ofa spinning top,when an external forceacting on the axis.
23 Earths Three Forms of Precession Precession of the AxisPrecession of the EllipsePrecession of the Solstices and the Equinoxes
24 1. Precession of the Earths Axis -One rotation every 25,000 years-Caused by the gravitational pull on the earth's equatorial bulge
28 2. Precession of the Ellipse - The ellipse of theearth’s orbit also hasa precession-Rate of precessionis even slower thanthat of the axialprecession~22,000 years
29 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.
30 One full rotation take between 19-23 Thousand years What does it look like?One full rotation take between Thousand years
37 Complication from overlapping cycles Searching for Orbital-scale Changes in Climatic Records
38 Time Series Analysis Power Spectrum Time Series Analysis A method used to analyze climate record data, in hopes to extract rhythmic cycles.References patterns against a time component.Spectral AnalysisReferencing 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.FilteringA method of honing in on a specific set of data to better analyze it without referencing other data.
40 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.
41 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.