CME/Flare Mechanisms

• Solar “minimum” event this January • For use to VSE must be able to predict CME/flare

Spiro K. AntiochosNaval Research Laboratory

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

Where does Eruption Occur?

07/14/00 event – from Schrijver et al 08/16/05 NASA Science Update

• Filament channel provides necessary energy for eruption

• For long range prediction (groups A & B), need to understand how they form (and what they are!)

Why does Eruption Occur?

(e.g., T. Forbes)

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(DeVore et al)

+- PIL

• 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

• 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

Models for CME Initiation

Breakout Model

(from Lynch et al )• Multi-polar field & footpoint shear• Reconnection removes overlying flux• CME due to run-away expansion, accelerates when flare turns on

Twisted Flux Rope Model

• 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

(Fan 2005 – flux “emergence”)(Amari et al 2003 – flux “cancellation”)

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

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)

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

Observational Signatures of Breakout

• Initial potential state • Filament channel grows• Stressed field and null

• Onset of breakout reconnection• Null and distant brightenings?

• Footpoint signatures move toward neutral line

• Onset of flare reconnection

• Flare ribbons move apart as usual

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

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)

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