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