CMEFlare Mechanisms

1
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

2
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
4
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)
5
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

6
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 )
7
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

8
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

9
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)

10
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

11
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

12
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

13
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)

14
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