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

2. 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

3. 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

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

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

6. Covered with turbulent convection cells: “Granulation” (1 Mm)
3. Photosphere
Temperature K
Covered with turbulent convection cells: “Granulation” (1 Mm)
“Supergranulation”
( Mm)

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

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

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

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

11. 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 …

12. Old Picture Atmosphere - static, T(r)

13. But - atmosphere is inhomogeneous
Many temperatures in same region

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

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

16. 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

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

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

20. 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 !

21. Just before totality
2nd Contact
Magnetic tubes “prominences”

24. 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

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

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

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

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

29. 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

30. 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]

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

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

33. 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 !

34. 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

35. 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)

36. 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