CMEFlare Mechanisms - PowerPoint PPT Presentation
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CMEFlare Mechanisms
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CME/Flare Mechanisms. Solar 'minimum' event this January ... see disturbance along spine, distant brightening (see also papers by Sterling & Moore et al) ... – PowerPoint PPT presentation
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Title: CMEFlare Mechanisms
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CME/Flare Mechanisms
Spiro K. Antiochos Naval Research Laboratory
- Solar minimum event this January
- For use to VSE must be able to predict CME/flare
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Present State of Understanding on CME/Flare
Mechanisms
- Know where eruption can occur
- Sheared filament channel
- Very robust indicator
- Promising ideas for why eruption occurs
- Reconnection and twisted flux rope models
- But not yet able to determine when
- Essential for predicting possible
geo-effectiveness - Observationally constrained
- Also need to determine how will erupt
- Essential for predicting SEPs
3
Where does Eruption Occur?
- Filament channel provides necessary energy for
eruption - For long range prediction (groups A B), need to
understand how they form (and what they are!)
07/14/00 event from Schrijver et al 08/16/05
NASA Science Update
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Why does Eruption Occur?
- Strongly non-potential field forms in narrow
region over polarity-inversion line - Exact topology still unobserved
- critical for eruption mechanism
- Held down by potential overlying coronal field
- Force balance breaks down and field expands
outward explosively producing CME, shock,
particles, etc. (see
following talk by Roussev) - Field reconnects below eruption to a more
potential state producing flare, X-rays, etc. - Generic to all models
-
PIL
-
(DeVore et al)
-
(e.g., T. Forbes)
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Models for CME Initiation
- Reconnection models (Resistive)
- Sheared 3D arcade topology (but not essential)
- Reconnection removes overlying field
- Tether-cutting reconnection inside filament
channel - Breakout reconnection outside filament channel
- Needs multi-polarity system
- Twisted flux rope models (Ideal)
- Twist is essential to pre-eruption topology
- Generally bipolar polarity region (not essential)
- Ideal (kink-like) instability/loss-of-equilibrium
moves aside overlying field
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Breakout Model
- Multi-polar field footpoint shear
- Reconnection removes overlying flux
- CME due to run-away expansion, accelerates when
flare turns on
(from Lynch et al )
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Twisted Flux Rope Model
(Fan 2005 flux emergence)
(Amari et al 2003 flux cancellation)
- Bipolar field with some process to form twisted
rope - Bulk of energy still in shear
- Rope lifts/kinks for some critical twist,
overlying field moves aside
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Why does Eruption Occur?
- Both breakout and twisted flux rope models shown
to produce fast eruption in idealized 3D
simulations - Role of tether-cutting still unclear
- Now testing with observed magnetic fields
- Beginning to incorporate better plasma energetics
- Need to incorporate better photosphere-corona
interaction - Flux emergence and cancellation
- But, overall, impressive progress has been made
in recent years
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When will Eruption Occur?
- Breakout onset of fast reconnection at coronal
null - Current sheet thins to critical scale
- Flux rope system reaches critical twist or
energy - Question needs more theoretical and numerical
study - Given answer, then in principle, could use
observations to determine coronal B - Effective extrapolation methods in use
- But B not measured in force-free region
- Perhaps some combination of observations will
work (need STEREO, SOLAR-B, and SDO)
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When will Eruption Occur?
- Given sufficiently accurate field (and driver),
could use numerical models to predict eruption - Reconnection calculate free energy see DeVore
poster
calculate growth of current sheets - Twisted rope calculate equilibrium and ideal
stability - But photospheric driving (emergence/cancellation)
may be difficult to predict - For near term, need to find pre-eruption
observational signatures - For breakout, pre-eruption reconnection
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Observational Signatures of Breakout
- Filament channel grows
- Stressed field and null
- Onset of breakout reconnection
- Null and distant brightenings?
- Initial potential state
- Footpoint signatures move toward neutral line
- Onset of flare reconnection
- Flare ribbons move apart as usual
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Signatures of Breakout in July 14, 1998 Flare
- Extrapolated potential field (Aulanier et al
2000) - Two-flux system embedded bipole, topology
identical to 3D breakout simulation
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Signatures of Breakout in July 14, 1998 Flare
- Overlying loops disappear before flare and see
disturbance along spine, distant brightening (see
also papers by Sterling Moore et al)
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Prospects for Future
- Theoretical/numerical work proceeding at good
pace - Have effective mix of groups, codes, expertise,
- Need to concentrate on resolving basic physics
questions - Will have revolutionary observations in few years
- Solar-B (and SOLIS) vector B fields ultra-high
resolution - 90? viewing from STEREO
- Multi-T images from SDO, spectroscopy from
Solar-B - Need campaign-style attack on
- How do filament channels form?
- What is their magnetic structure?
- Both theory and observations should be ready by
Sentinels - Provide in situ tests for CME/flare mechanisms
- Determine structure of eruption near Sun
- Connect eruption to particle production
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