Flows in NOAA AR 8210: An overview of MURI progress to thru Feb.’04
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Flows in NOAA AR 8210: An overview of MURI progress to thru Feb.’04
• Modelers prescribe fields and flows (B, v) to drive eruptions in MHD simulations
• MURI goal: use data to do this! Must find (B, v).• IVM & MDI tell us B. How do we get v?• LCT: commonly used method, but not acceptable!• MEF: developed by UCB-MURI.• ILCT: modified LCT, developed by UCB-MURI.• NOAA AR 8210 Results
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Q: Can we simulate relevant CME process(es)?
Traditionally, modellers:
1. start with magnetic field configuration B(x,y,z),
2. then drive boundary with velocities v(x,y,t) to store
energy and, perhaps,
3. trigger an eruption!
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MURI: drive simulations directly from data
1. Start with photospheric mag’gram (IVM data just presented)…(*)
2. and best guess at initial field topology (also just presented)…(*)
3. then evolve with MHD simulations, consistent w/photospheric evolution, conserving topology along the way
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Q: How do we get velocities from magnetograms?
24 hour MDI movie on 1 May 1998
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Three Velocity Reconstruction Methods
1. Local Correlation Tracking (LCT)
2. Minimum Energy Fitting (MEF)
3. Induction + LCT (ILCT)
• LCT:
i) cross-correlate subregions between two images;
ii) find shift that maximizes cross-correlation;
iii) interpret shift as velocity? tricky!LCTu
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LCT applied to MDI data
• Note shear across neutral line near (10,40) --- track (+/-) indep.• Note flux emergence near (50,70) --- fools LCT!
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Minimum Energy Fitting (MEF):
• LCT can’t drive codes: no vz, not consistent with
• We developed method consistent w/z-comp. of ideal induction equation:
• Represent unkown vector fields w/potentials:
tB
)vB-Bv(E)(1
t
Bzzz
z
c
)z (vB-Bv zz
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MEF, cont’d:
• Induction eqn. determines :
• Constrain by minimizing integrated velocity field, – this quadratic form resembles ‘energy,’ hence “MEF.”– assumes
• Solution v(x,y) is “as small as possible, consistent with the data.”
2z
t
B
)v( 2z
2vda
0Bv
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• Apparent horizontal motion can be either true horizontal motion, or vertical motion of a tilted field geometry.
zzzzz
vB - vB uBvB
B - v u
ILCT: Reinterpret LCT, a la Demoulin & Berger (2003)
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ILCT, cont’d: Find
• Similar to MEF, use scalar potentials:
• As w/MEF: indn eqn. fixes ; ass’d.
• Instead of minimizing ‘energy’ to find , ILCT uses LCT to constrain :
)uB( 2LCTz
)z (vB-BvuB- zzz
0Bv
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These data used in our AR 8210 simulations. (*)
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Conclusions Re: I-LCT, MEF
• Some method of deriving from data is required to drive MHD codes.
• Method must be consistent with magnetic field evolution, . (Will use .)
• UCB-MURI team has developed two novel methods, where none existed before.
• Our methods are only consistent with --- still more work to be done!
zv,v
tB
tBz
0Bv
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Amari et al. Initial Velocity
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Cancellation flow in Amari et al.
(BACK)
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Vector Field in AR 8210, c. 1 May Eruption
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NLFFF of AR 8210, from S.Regnier
(BACK)
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Data-driven ZEUS Run
(BACK)
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Q:What is the proximate cause of CMEs?
• Energization: Field emerges (twisted?); flows in high- photosphere stress ‘line-tied’ coronal field.
• Impulsive Release: Corona undergoes massive, violent restructuring: a CME
• Released Energy: is stored in currents, both those present at emergence and those induced by flows
‘STORAGE & RELEASE’ PARADIGM