SUN COURSE - SLIDE SHOW 8

Today: Solar flares & coronal mass ejections (CME’s)

1. Introduction - Sunspot Numbers

Corona Changes with Solar Cycle

Coronal Mass Ejections (see talk 3)SOHO Coronagraph -- Artificial eclipse

Can reach Earth - communications / satellites

Discovered huge ejections of plasma

2. Northern Lights(Aurora)

The Magnetic Field of the Earth•The Earth’s magnetic field is like that of a bar magnet close to the Earth

• The solar wind distorts the magnetic field into a comet like shape on the nightside (the magnetotail).

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Astronaut safety:Enhanced radiation levels

Telecommunicationand power lines

Indirect effects of CME impact

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What causes the aurora ?

Distortion of Earth’smagnetic field by CMEenergizes particles inthe magnetotail.

These particles hit themolecules of the upperatmosphere and makethem glow

Different colours: different molecules (oxygen, nitrogen), also the level of excitation of the molecules

What accelerates the particles ?

The Earth’s magnetic field shields us from any direct effects of CME’s !

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Reconnection in the tail

Energetic particles move along the magnetic field, andhit the atmosphere close to the north and south poles !

Aurora pictures taken from the Space Shuttle

Height of auroral emission: 100-400 km (60 - 200 miles)

Space shuttle orbit hassimilar height, so theSpace shuttle can go directly through the aurora !

Photo sphere

from SOHO

3. On October 28, 2003

Magnetic field

from SOHO

X-ray Intensity(t) -3rd largest

Outer Corona

from SOHO

CME 2000 km/s

(5 times faster than

normal)

Snow -- relc

particles

1 Week Later - Fireworks ContinuedSOHO Site (Nov 6):

Just as solar scientists were ready to start breathing normally again, active region 10486 blasted off yet another mega-flare. This one saturated the X-ray detectors on the NOAA's GOES satellites; the jury was therefore out for a while on the definitive classification of the flare -- speculations ranged from simply well above X20, to X40 or even X50. Today word came from the SEC that their best estimate was X28.

It is now official: We have a new number 1 X-ray flare for the record books.

The biggest solar flare ever recorded !

X-ray intensity(t)

Conjuring trick --

plasma appearing by magic ?

Close-up of plasma motions

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Solar Flare

Very sudden brightening in corona

-- due to appearance of heat

Occurs above complex sunspots

The only possible source of vast amount of energy - B

Heating is ohmic ( )

€

j 2 /σ

How do large currents appear ??

How is magnetic energy converted into heat (reconnection) ?

4. Overall Picture of Solar Flare

In core - magnetic tube twisted (energy stored in fff)

- erupts (catastrophe) - drives reconnection

Reconnection heats loops/ribbons

Reconnection proceeds -- loops rise

Chromosphere

Reconnection heats loops/ribbons

Reconn. Accelerate p’cles --> hard X

(Priest and Schrijver 1999)

Reconnection heats loopsContinues:new loops

form &evaporate.

Old loops cool & drain

Feet move apart

Ex of Loops Rising

Same process

for eruptions

outside a.r.

Ex of rising cusp

Before: twisted, force-

free -->

energy stored

Example from

SOHO

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TRACE - 1st image of j sheet

RHESSI Overlay of TRACE

•Blue contours: X-rays from very high energy particles

•Red contours: X-rays from high energy pcls

Reconnection accelerates particles --> hard X

Effects: (i) creates

wave

(ii) Wave --Movie from TRACE

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Cause of Eruption ?

Magnetic Catastrophe

2.5 D Model

Numerical Model

Suggestive of

Catastrophe

Cause of energy release

-- reconnection

When an X-point collapses

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Reconnection converts energy

Future Space Observatories

STEREO (NASA)* Two satellites* Stereoscopic images of corona

Solar Orbiter (ESA)* 3 times closer than Mercury

Solar Dynamics ObservatorySuccessor to SOHO(super - MDI + Trace)