APPLICATIONS of RECONNECTION

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APPLICATIONS of RECONNECTION
1. The CORONA
Yohkoh Bright Pts Loops Holes
A magnetic world Tfew MK
How is the Corona Heated ?
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Recent Space Observations

• Low-freq. waves
• -- few obsns in plumes and flare-excited loops
• High-freq. waves
• -- ? heating outer corona
• Most evidence (low corona)
• --gt

reconnection
elegant explanation for many diverse phenomena
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How is Reconnection Working in Corona ?
(i) Drive Simple Recon. at Null by photc.
motions --gt X-ray bright point
Supported by TRACE
(ii) Binary Reconnection -- motion of 2
sources (iii) Separator Reconnection --
complex B
(iv) Braiding (v) Coronal Tectonics
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(ii) Binary Reconnection
Many magnetic sources in solar surface

• Relative motion of 2 sources -- "binary"
  interaction
• Suppose unbalanced and connected --gt Skeleton

• Move sources --gt "Binary" Reconnection
• Flux constant - - but individual B-lines
  reconnect

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Cartoon Movie (Binary Recon.)

• Potential B
• Rotation of one Source about another

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(iii) Separator Reconnection

• Relative motion of 2 sources in solar surface
• Initially unconnected

Initial state of numerical expt. (Galsgaard
Parnell)
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Comput. Expt. (Parnell / Galsgaard
Magnetic field lines -- red and
yellow Strong current Velocity isosurface
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(iv) Braiding
Parkers Model
Initial B uniform / motions braiding
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Numerical Experiment (Galsgaard)
Current sheets grow --gt turb. recon.
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Current Fluctuations
Heating localised in space -- Impulsive in time
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(v) CORONAL TECTONICS
? Effect on Coronal Heating of Magnetic Carpet

• (I) Magnetic sources in surface are
• concentrated

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(II) Flux Sources Highly Dynamic
Magnetogram movie (white ve , black -ve)

• Sequence is repeated 4 times
• Flux emerges ... cancels

• Reprocessed very quickly (14 hrs !!!)

? Effect of structure/motion of carpet on
Heating
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Life of Magnetic Flux in Surface

• (a) 90 flux in Quiet Sun emerges as ephemeral
  regions (1 per 8 hrs per supergran, 3 x 1019 Mx)

• (b) Each pole migrates to boundary (4 hours),
  fragments --gt 10 "network elements" (3x1018 Mx)

• (c) -- move along boundary (0.1 km/s) -- cancel

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From observed magnetograms - construct coronal
field lines
- statistical properties most close low down
Time for all field lines to reconnect
only 1.5 hours
(Close, Parnell, Priest)
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Coronal Tectonics Model

• (Priest, Heyvaerts Title)
• Each "Loop" --gt surface in many sources

• Flux from each
• source topology
• distinct --
• Separated by
• separatrix surfaces

• As sources move, coronal fields slip
  ("Tectonics")
• --gt J sheets on separatrices separators
  --gt Reconnect --gt Heat

• Corona filled w. myriads of separatrix/separator
  J sheets, heating impulsively

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Fundamental Flux Units

• Intense tubes (B -- 1200 G, 100 km, 3 x 1017 Mx)

not Network Elements

• Each network element -- 10 intense tubes

• Single ephemeral
• region (XBP) --

100 sources
800 seprs, 1600 sepces

• Each TRACE
• Loop --

10 finer loops
80 seprs, 160 sepces
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TRACE Loop
Reaches to surface in many footpoints.
Separatrices form web in corona
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Corona - Myriads Different Loops
Each flux element --gt many neighbours But
in practice each source has 8 connections
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Theory

• Parker -- uniform B -- 2 planes -- complex
  motions
• Tectonics -- array tubes (sources) -- simple
  motions

• (a) 2.5 D Model
• Calculate equilibria --
• Move sources --gt
• Find new f-f equilibria
• --gt Current sheets
• and heating

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3 D Model

• Demonstrate
• sheet formation
• Estimate heating

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Results

• Heating uniform along separatrix
• Elementary (sub-telc) tube heated uniformly

• But 95 photc. flux closes low down in carpet
• -- remaining 5 forms large-scale connections
• --gt Carpet heated more than large-scale corona

• So unresolved observations of coronal loops
• --gt Enhanced heat near feet in carpet
• --gt Upper parts large-scale loops heated
  uniformly less strongly

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2. SOLAR FLARES CMEs
SOHO Coronagraph -- Artificial eclipse
Discovered huge ejections of plasma
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? Effect on the Earth -- Space Weather
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Aurora
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Other Consequences
Damage to satellites, astronauts Disruption to
radio/phone communications, power grids
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On October 28, 2003
Photo sphere from SOHO
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Magnetic field
from SOHO
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X-ray Intensity(t) -3rd largest
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Outer Corona from SOHO
CME 2000 km/s (5 times faster than normal)
Snow -- relc particles
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Aurora in St Andrews on Wed
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Thurs
Thurs
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1 Week Later - Fireworks Continued
- the biggest solar flare ever recorded !
X-ray intensity(t)
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Nov 4 SOHO coronal image (1.6 MK)
1st5 hours
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Nov 4 EIT 284 (2.0 MK)
every 6 hours
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Compare Temps 80,000 K, 1.6 MK, 2.0 MK
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Close-up of plasma motions
Conjuring trick -- plasma appearing by magic ?
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2.1 Eruption

• N.B.
• Flare CME are part of 1 magnetic eruptive
  process
• (short MHD connection time)

• Role of filament/prominence -- indicator of
  high
• shear
• So perhaps eruption is driven more from core,
  where
• most energy is stored

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Overall Picture of Eruption
In core - magnetic tube twisted (energy stored
in fff rather than current sheet) - erupts
(catastrophe or breakout) - drives reconnection
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Reconnection heats loops/ribbons
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Reconnection heats loops/ribbons
Chromosphere
Reconnection proceeds -- loops rise
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Reconnection heats loops
Continuesnew loops form evaporate. Old loops
cool drain Feet move apart
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Example from SOHO
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Example from TRACE (171 A)
1 MK (Fe IX) 20 MK (Fe XVI)
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RHESSI Overlay of TRACE

• Red contours 12 25 keV X-ray flux.

• Blue contours 50 100 keV X-ray flux.

• Particle acceleration
• DC acceleration in sheet Fermi in collapsing
  trap
• ? Shock acceleration

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Cause of Eruption ?
Magnetic Catastrophe
2.5 D Model
(or a breakout)
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Numerical Model
Suggestive of Catastrophe
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3. CONCLUSIONS

• Understanding how B interacts with plasma
• Key to many solar system phenomena

• Two main equations
• Induction equation -- advection diffusion
• Eqn. motion -- magnetic tension pressure
  forces

• Reconnection - difft roles in coronal heating -
  binary, sepr, braiding
• XBP - usually driven reconnection
• High corona -- ? high-frequency waves
• Coronal loops -- ? turbulent reconnection

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• Need in future
• Effect magnetic carpet
• Effect complex magnetic topology
• Test viability of Coronal Tectonics Model

• Develop 3D reconnection theory

• Bright new students, like you !

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FINALLY -- the MAIN QUESTION
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