I. OUR OWN SUN(Space Climate School, Saariselka, March, 2009)

Eric Priest (St Andrews)

1. Of great scientific interest in own right

2. Influence on Earth

3. Important for Astronomy

-- fundamental cosmic processes

Many basic properties still mystery (astrony) - interior, dynamo, corona, wind,

flares

4. Many misconceptions…..

1. Why Study the Sun ?

So Sun is 1 of liveliest branches of space physics/astronomy

Sun is NOT a normal gas

B and plasma -- coupled (intimate, subtle)

behaves differently from normal gas:

Another Theme:Many surprises caused by magnetic field (B)

Sun is in 4th state of matter("PLASMA")

B exerts force on plasma -- stores energy

Vital Statistics

? Chemical composition

2. The SUN

RadiusAge --

Interior:Core

Convection zone

(> 0.7 R0)

Atmosphere: Photosphere, Chromosphere, Corona

Overall Structure

Covered with turbulent

convection cells: “Granulation”

(1 Mm)“Supergranulation”

(15 - 30 Mm)

3. PhotosphereTemperature 6000 K

In close-up:

points, flowers, ribbons

(created by magnetic

fields)

Photosphere --> Sunspots

Harriot discovered (1610) w. telescope

Dark because cool But why cool ?

SUNSPOTS

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"

2. Patterns of sunspots/act. regs-- large flux tube--> dynamo …

1. Intense magnetic fields over whole Sun

SURPRISES: --

B carried to edges of

convection cells

Old Picture Atmosphere - static, T(r)

But - atmosphere is inhomogeneousMany 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

Continually-changing threads

Quiet active region H-alpha

0.1 arcsec

("crown") -- See at ECLIPSE of Sun

SURPRISE (1940) -- Temperature is million degrees

5. CORONA

Heating caused by magnetic fieldStructure outlines magnetic fieldAlong open structures: -- fast solar windStudents in St Andrews imaginative:

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

ProminencesCorona - glowing against jet black disc !

2nd ContactJust before totality

Magnetic tubes “prominences”

Normally need eclipse to see -- Glare of surface

Observe direct with EUV/X-ray telescope

As T increases (furnace), object becomes bluer

CORONA:

Coronal holes -- loops -- bright points Bright --> Denser

Picture with X-ray telescope:

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

6. SOHO (Solar & Heliospheric Observatory)

Observing Sun continuously for 1st time (ESA/NASA)

Launched 1995. Orbiting Sun at point in phase

with Earth

MANY NEW SURPRISES

--> 1st comprehensive view of Sun

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)

Sunspot minm -- no spots -- polar fields

[Polar Fields: * maximum extent at s. minimum * change polarity 1-2 years after s. maximum]

Spots emerge at high latitudes w. opposite polarity[later at lower latitudes]

90% active region flux cancels --10 % migrates -- following flux reaches polesreduces & reverses polar field-- new minm

Global coronal magnetic field goes thro’ complex set of 17 topologies(Maclean & Priest, 2007)

Whole atmosphere varies with cycle

Chromosphere

Corona (Intensity Changes by 100)

Max Min

Schematic --> eq. streamers/polar holes

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]

Solar wind velocity [polar plot, ULYSSES]

SURPRISE (1976)

"Maunder Minimum" -- Little Ice Age

Realised NO sunspots in most of 17th centy

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:

1400 from 10Be in ice cores30, 000 yrs BP from 14C in tree rings (J Beer)

1980 from several spacecraft [irradiance]

7. CONCLUSIONS

Solar Physics - golden age - observations

Sense of vitality will continue

Magnetic theory playing a key role

- amazing observations from space(SOHO, TRACE, RHESSI,

Hinode, Stereo, SDO, Orbiter)

- bright new young students