modelling magnetic reconnection and nanoflare heating in the solar corona the coronal heating...
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Modelling Magnetic Reconnection and Nanoflare Heating in the Solar
Corona
The Coronal Heating Problem
George BiggsAdvisors: Mahboubeh Asgari-Targhi & Nicole Schanche
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Why is the corona so hot?
Two main complementary theories:Alfvenic turbulence (1-3MK, stable heating)Flare heating (3-10MK, rapid dynamic heating)
Nanoflare heating can be influenced by Alfvenic turbulence
Image: National Geographic 2011/06. EUV view.
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Why Nanoflares?
• Hudson (1990) explored microflares
• Follow a power law with parameter of -1.8, this is too low to explain the observed heating
• Concluded a power law fit of over -2 is required
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Magnetic Reconnection
• Removes one crossing
• Depends on critical crossing number
• Only occurs in highly stressed situations
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Magnetic Energy and Crossing Number
Efree ∝
Image created using non-linear force free field fitting in CMS, HI-C data, 193 Å
B min = 381.05 GaussRadius = 191.7kmLength = 43.8Mm
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Braidwords -Modelling braided fluxtubes
• Complex crossings can be represented by a ‘braidword’• Braidword corresponds to string of integers representing crossings
Image on right (1,3,1,-4,2,-4,2,-4,3,-2,-4)
Images: Braidword examples from mathworld.wolfram.com
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Avalanche Model
• Analogy is a sand pile, once criticality is reached a small addition triggers avalanche
• Can be applied to reconnection
• In reconnection twisting motions of foot points are “grains of sand” being added
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Reconnection In Action
• Initial braidword {-1, -3, -1, 4, -2, 4, -2, 4, -2, 4, 4, 4, 4, -3, 2, 4, 4, 4, 4, -2, 1, 1, 1, -3, -2, 3, -1, -1, -1, 2, -4, -4, -4, -4, -2, 3, -4, -4, -4, -4, 2, -4, 2, -4, 2, -4}
• First reconnection occurs removing -2 crossing
• Final braidword {-1, -3, -1}
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Methods and Predictions
• Expect a power law distribution
• Initial parameters (B min, length, diameter) from the previously shown non-linear force free field modelling gives minimum crossing number
• Found parameters for energy simulation by running reconnection simulation with parameters optimised through repeated trials
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Finding Parameters• Analysed the results to see what the best fit was• Braidsize 10000, Reconnections 10000, Runs 500, Power Law -3.41401• Braidsize 500, Reconnections 1000, runs 500, Power Law = -3.02347
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Results Found power law fit as expected, approx. -2.8
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How This Dynamic Approach Differs
• Zirken&Cleveland(1992) modelled nanoflares using grid randomly depositing energy
• Longcope&Noonen(2000) also uses grid but evenly spaces opposite poles
• Both have shortcomings avoided in this analysis
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Comparison to Observation
• Analysed the Hi-C (High-Resolution Coronal Imager)region to determine the number of flares in the two day period surrounding Hi-C
• Expect distribution in types of flares with smaller more likely consistent with power law
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Results Of Observations
7/10/12 0:00 7/10/12 12:00 7/11/12 0:00 7/11/12 12:00 7/12/12 0:00 7/12/12 12:00 7/13/12 0:000
5
10
15
20
25 Distribution of Flare Intensities
Time Of Event
Stre
ngth
Of E
vent
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Past and Future
• Updated modelling of reconnection to include avalanche model
• Ran simulations using this updated model and found a power law as expected
• To the future: Increase sophistication of model further by including internal twist
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AcknowledgmentsAdvisors Dr Mahboubeh Asgari-Targhi & Nicole Schanche and help from Patrick McCauley
Dr. Henry “Trae” Winter, Dr. Kathy Reeves and the REU programme. NSF-REU solar physics programme at SAO, grant number AGS-1263241.
AIA contract SP02H1701R from Lockheed-Martin to SAO.
We acknowledge the High resolution Coronal Imager instrument team for making the flight data publicly available. MSFC/NASA led the mission and partners include the Smithsonian Astrophysical Observatory in Cambridge, Mass.; Lockheed Martin's Solar Astrophysical Laboratory in Palo Alto, Calif.; the University of Central Lancashire in Lancashire, England; and the Lebedev Physical Institute of the Russian Academy of Sciences in Moscow.