(Space Climate School, Saariselka, March, 2009) I. OUR OWN SUN (Space Climate School, Saariselka, March, 2009) Eric Priest (St Andrews)

space physics/astronomy 1. Why Study the Sun ? 1. Of great scientific interest in own right 2. Influence on Earth 3. Important for Astronomy -- fundamental cosmic processes 4. Many misconceptions….. Many basic properties still mystery (astrony) - interior, dynamo, corona, wind, flares So Sun is 1 of liveliest branches of space physics/astronomy

Another Theme: Many surprises caused by magnetic field (B) Sun is NOT a normal gas Sun is in 4th state of matter ("PLASMA") behaves differently from normal gas: B and plasma -- coupled (intimate, subtle) B exerts force on plasma -- stores energy

2. The SUN Vital Statistics ? Chemical composition Radius Age --

Overall Structure Interior: Core Convection zone Atmosphere: Photosphere, Chromosphere, Corona

Covered with turbulent convection cells: “Granulation” (1 Mm) 3. Photosphere Temperature 6000 K Covered with turbulent convection cells: “Granulation” (1 Mm) “Supergranulation” (15 - 30 Mm)

In close-up: points, flowers, ribbons (created by magnetic fields)

Dark because cool But why cool ? SUNSPOTS Photosphere --> Sunspots Harriot discovered (1610) w. telescope Dark because cool But why cool ?

New Model (Thomas & Weiss) Mixture: Dark filaments- (low) Bright filaments- (high)

Map of Photospheric Magnetic Field White -- towards you; Black -- away from you Regions around sunspots -- bipolar "Active Regions"

SURPRISES: -- B carried to edges of convection cells 1. Intense magnetic fields over whole Sun B carried to edges of convection cells 2. Patterns of sunspots/act. regs -- large flux tube --> dynamo …

Old Picture Atmosphere - static, T(r)

But - atmosphere is inhomogeneous Many temperatures in same region

4. Chromosphere is dynamic (2D Simulation) [Hansteen & Carlsson] Corona Chromo- sphere Photo- sphere (light/ dense)

Dynamic nature s. atmosphere Swedish Solar Telescope Quiet active region H-alpha 0.1 arcsec Continually-changing threads

5. CORONA Heating caused by magnetic field ("crown") -- See at ECLIPSE of Sun 5. CORONA Along open structures: -- fast solar wind SURPRISE (1940) -- Temperature is million degrees Students in St Andrews imaginative: Heating caused by magnetic field Structure outlines magnetic field

Total Eclipse - March 29, 2006 - Motion of Moon’s shadow

Over 1.5 hours: Light level decreases, Cooler, Shadows sharpen

In last 10 minutes: Light level and temperature decrease more quickly Wind Start to see planets Just before totality (when Moon covers Sun) -- Baily beads Red chromosphere Prominences Corona - glowing against jet black disc !

Just before totality 2nd Contact Magnetic tubes “prominences”

CORONA: Observe direct with EUV/X-ray telescope Normally need eclipse to see -- Glare of surface Observe direct with EUV/X-ray telescope As T increases (furnace), object becomes bluer

Picture with X-ray telescope: Coronal holes -- loops -- bright points Bright --> Denser

Hinode X-ray Telescope (2006--..)

6. SOHO (Solar & Heliospheric Observatory) Launched 1995. Orbiting Sun at point in phase with Earth Observing Sun continuously for 1st time (ESA/NASA) --> 1st comprehensive view of Sun MANY NEW SURPRISES

QN. -- ? Earth Influenced by Solar Variability Number of Sunspots Oscillates w. 11-year Cycle

Solar Cycle Sunspots - two zones between -35o and +35o latitude Leading spots have opposite polarities in 2 hemispheres [Hale] Leading polarity is closer to equator [Joy] Magnetic field reverses every 11 years

Solar cycle (ii) Spots emerge at high latitudes w. opposite polarity Sunspot minm -- no spots -- polar fields Spots emerge at high latitudes w. opposite polarity [later at lower latitudes] 90% active region flux cancels --10 % migrates -- following flux reaches poles reduces & reverses polar field-- new minm Global coronal magnetic field goes thro’ complex set of 17 topologies (Maclean & Priest, 2007) [Polar Fields: * maximum extent at s. minimum * change polarity 1-2 years after s. maximum]

Whole atmosphere varies with cycle Max Min Chromosphere Corona (Intensity Changes by 100) Schematic --> eq. streamers/polar holes

Solar wind velocity [polar plot, ULYSSES] Sunspot minimum [1994-95] FAST Solar Wind (700 km/s) in coronal holes SLOW Solar Wind (300 km/s) in equatorial streamers [Red = inward field Blue = outward field]

SURPRISE (1976) Realised NO sunspots in most of 17th centy "Maunder Minimum" -- Little Ice Age So B on Sun affects climate of Earth !! But mechanism not known !

SOHO --> Total Emission (t) 1996-2000 Emission varies by 0.2% -- passage sunspots Increase by 0.1% from sunspot min to max Much too small to produce global warming ?? Real & ?? cause

Solar cycle variations further back to: 1980 from several spacecraft [irradiance] 1400 from 10Be in ice cores 30, 000 yrs BP from 14C in tree rings (J Beer)

amazing observations from space CONCLUSIONS Solar Physics - golden age - observations Magnetic theory playing a key role Sense of vitality will continue amazing observations from space (SOHO, TRACE, RHESSI, Hinode, Stereo, SDO, Orbiter) - bright new young students