sun course - slide show 5
DESCRIPTION
SUN COURSE - SLIDE SHOW 5. Introduction,MHD Eqns, Induction eqn, Coronal loops. SUNS POTS. 1. OBSERVATIONS. Existence known since 350 BC (Greece), 28 BC (China). Sunspots. In West, no ref until 850 AD; Galileo (1611). Umbra Penumbra. Site strong B. Flux tube - ?? Model. - PowerPoint PPT PresentationTRANSCRIPT
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Introduction,MHD Eqns, Induction eqn, Coronal loops
SUN COURSE - SLIDE SHOW 5
SUNS POTS
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1. OBSERVATIONS
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SunspotsExistence known since 350 BC (Greece), 28 BC (China)
In West, no ref until 850 AD;
Galileo (1611)
Site strong B.
Umbra
Penumbra
Flux tube - ?? Model
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Dark because Cool
1600 K cooler than photo.
?? Why cool
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LATEST IDEAS on NATURE of SUNSPOTSIntroduction
Observed over 2000 years
Hale (1908): strong B (3000G cf mean q Sun 3 - 20 G)
Outside sunspots: strong small-scale convn (gran, 1 Mm) + weak larger-scale convn (supergran, 15 Mm)
Umbra - (15 Mm, B strong, vertical) dark -- cool, inhibition of convection
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Penumbra (40 Mm, B intermed, inclined) radial light/dark filaments
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NEW THEORY - Weiss et al (2004)
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Stunning Image(Swedish
telescope, La Palma)
Penumbral structure
created by B
Close-up of penumbra -> new surprises:
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QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Points moving along lanes; Bright flows in/out;
Strange dark cores
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SURPRISES: -- patterns of sunspots
-- why ?
2. SOLAR CYCLE
Magnetogram
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In interior, plasma dominates --> moves B
Rotation shears B
Magnetic Field (B) and Plasma Coupled
B exerts force on plasma -- move together
--> 2 tubes B --> Emerge:
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Magnetic Tube Emerges
Creates pair of sunspots +/-
Opposite pattern in s. hemisphere
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Global Magnetic Field of Sun
mixed polarity -- at edge of supergranule cells -- covers Sun at s. minimum
ephemeral active regions (1019 Mx) -- emerge & migrate to boundary
--> network fragments (F = 2x1018 Mx, B = 1 kG) -- at edges of cells
internetwork fragments (F = 6x1016 Mx, B = 10-100 G ?) -- inside cells
(i) Quiet Sun - NetworkAt photosphere <|B|> ~ 3 - 20 G, but most is strong (1 kG) & vertical
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(ii) ACTIVE REGION FLUX
Spreads out --> remnant active region
Merges --> unipolar region -- one dominant polarity
Migrates to the poles --> polar field
Emerges as
•sunspots (B = 3 kG, flux = 1022
Mx)
* active regions --> faculae (bright)
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Solar Cycle Sunspots vary with period 8-15 years (average 11.1 yr) Two zones between -35o and +35o latitude
In opposite hemispheres, leading spots have opposite polarities (Hale) Leading polarity is closer to equator (Joy)
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New spots emerge at start of cycle at high latitudes w. opposite polarity
As cycle progresses, spots form at lower latitudes (Sporer)
Polar Fields: * maximum extent at s. minimum * change polarity 1-2 years after s. maximum
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No sunspots varies - 11-year
cycle
Also cycle in X-rays
And in shape of corona:
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Chromosphere
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SOHO (Solar & Heliospheric Observatory)
Orbiting Sun at L1 point in phase with Earth Observing Sun continuously for first time
QuickTime™ and aSorenson Video decompressorare needed to see this picture.
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? Earth Influenced by Solar Variability
Number of Sunspots Oscillates w. 11-year Cycle
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SURPRISE (1976)
"Maunder Minimum" -- Little Ice AgeSo B on Sun affects climate of Earth !!
How ??
Realised NO sunspots in most of 17th centy
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SOHO --> Total Emission (t) 1996-2000
Emission varies by 0.2% --
passage sunspots
Increase by 0.1% from sunspot min
to max
? Contribution to global warming
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SURPRISE (2001)Discovered that Global B of Sun doubled since 1900
Observed increase in T (blue)Best estimate of increase caused by Sun (yellow)
Only 1/3 global warming (1970 to 2000) caused by Sun
? Mechanism couple Sun/climate
? Effect on Global T of Earth