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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 Presentation
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Introduction,MHD Eqns, Induction eqn, Coronal loops
SUN COURSE - SLIDE SHOW 5
SUNS POTS
1. OBSERVATIONS
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
Dark because Cool
1600 K cooler than photo.
?? Why cool
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
Penumbra (40 Mm, B intermed, inclined) radial light/dark filaments
NEW THEORY - Weiss et al (2004)
Stunning Image(Swedish
telescope, La Palma)
Penumbral structure
created by B
Close-up of penumbra -> new surprises:
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Points moving along lanes; Bright flows in/out;
Strange dark cores
SURPRISES: -- patterns of sunspots
-- why ?
2. SOLAR CYCLE
Magnetogram
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:
Magnetic Tube Emerges
Creates pair of sunspots +/-
Opposite pattern in s. hemisphere
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
(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)
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)
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
No sunspots varies - 11-year
cycle
Also cycle in X-rays
And in shape of corona:
Chromosphere
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.
? Earth Influenced by Solar Variability
Number of Sunspots Oscillates w. 11-year Cycle
SURPRISE (1976)
"Maunder Minimum" -- Little Ice AgeSo B on Sun affects climate of Earth !!
How ??
Realised NO sunspots in most of 17th centy
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
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
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