CME/Flare Mechanisms Solar “minimum” event this January For use to VSE must be able to predict CME/flare Spiro K. Antiochos Naval 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) (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