sun course - slide show 8 today: solar flares & coronal mass ejections (cme’s)
TRANSCRIPT
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)