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Working Group E: The Pre-CME Sun
- Pre-eruption structure, evolution & energy release
- Global issues: helicity, homologous CMEs
- Inputs to CME initiation models
N. Gopalswamy
From First Elmau CME workshop
PresentationsPresenter Topic/Question Future Plans
J.-L. Bougeret Global Sun Homolog. CMEs
R. Canfield Separatrix surfaces, s CDAW 1999 data for CME- connection
S. Antiochos Bipoleshear
Seehafer -effect builds up helicity; released in CMEs
Use SOHO/MDI data
D. Maia Nonthermal brightening & Filament eruption
Do statistics
N. Gopalswamy Microwave filament &X-ray brightening
Chen/Shibata Filament Eruption & Emerging Flux
Simulation
K. Dere AR evolution & CMEs Use Lara et al. (2000) method
N. Gopalswamy Photospheric B flux change Do Statistics
S.Antiochos Inputs to CME models
N. Gopalswamy Nonradial Motion of filaments
Structure of CMEs
• Frontal structure
• Cavity
• Prominence Core
• Post-eruption Arcade (Two-ribbon in H-alpha, arcades in X-ray, EUV)
• Note: Not all structures are present in all CMEs!
‘Cavity’ in Eclipse Pictures
Where do CMEs originate?
• CMEs originate from closed field regions
- Active Regions
- Filament regions
- Combination of AR and Filament regions
- Transequatorial interconnecting regions
Closed Field Regions: Where one should look for pre-CME signatures
TIL
Filament
Active region
SOHO/EIT image 195 A H-alpha picture
• Structure (Sigmoids, Flux Ropes)
• Evolution (Flux Emergence, Flux cancellation, Shear, Twist)
• Energy Release (Small-scale Heating & Particle Acceleration)
Aspects of Pre-eruption Phase
Three-part structure before eruption (Yohkoh/SXT)
• Frontal (but sheared)
• Cavity hidden?
• Filament core
Pre-Eruption Structure:Sigmoids
• S- and reverse S-shaped structures in X-ray images of Active Regions (Rust & Kumar 1996).
• Erupt more often than non-sigmoidal regions (Canfield et al. 1999); Beware of apparent “sigmoids” (Glover et al., 2000)
• Relation to white light CMEs being studied• Coronal counterpart of photospheric shear?
(Ambastha et al., 1993)
Pre-eruption Structure: Flux ropes
• Naturally support prominences (Linker et al., 2001)
• Often observed as dark cavity in eclipse pictures• Formed before (Low, 2001) or during (Gosling et
al., 1990) eruption?• Interplanetary Magnetic Clouds are flux ropes
(Burlaga et al.,1981) • MC formed out of filament or cavity of the white
light CME? (Bothmer & Schwenn, 1994; Gopalswamy et al., 1998)
Pre-eruption Structure:Guiding Streamers
• Non-radial motion of filaments
• Obvious during Solar Minimum
• Latitudinal distribution of CMEs peaks near the equator; associated solar sources peak near the active region belt
The solar dipole field has strong influence on CME propagation
CME CPAs equatorward of
Prominence CPA during min
• Compared 186 microwave prominences with LASCO CMEs during 1996-2001
Pre-eruption Evolution• Substantial Flux emergence near filament before
eruption; polarity of new flux favorable for reconnection (Feynman & Martin, 1995)
- Confirmed by numerical simulation studies (Chen & Shibata, 2000)
• Significant changes in photospheric flux in small areas in the eruption region (Lara et al., 2000)
• CMEs without flux emergence also observed (Subramanian & Dere, 2001; Wang & Sheeley, 1999)
• Reconnection-favoring flux emergence
Simulation supports preeruption Reconnection (Chen & Shibata 2000)
• Flux emergence under the filament
• Flux emergence from the side
A transequatorial Eruption
• EIT 195 A difference image showing dimming at 08:36 UT
• LASCO image at 08:56 UT
Weak Dimming Before Eruption
AR-Active Region D-DimmingG- GOES X-ray Flux
Pre-eruption Evolution: Prolonged Dimming
• Weak, prolonged dimming for ~ 1 hr (Gopalswamy et al., 2001)
• Small-scale opening of field lines resulting in the eruption of underlying structure? (Antiochos et al., 1994)
Pre-eruption Energy Release
• Small-scale heating near filaments - consistent with reconnection scenario• Particle Acceleration- Radio bursts (400 MHz) near filaments
(Maia et al.)- Minutes before filament eruption- nonthermal energy release due to
reconnection
Filament Eruption Onset
Models: Goal & Observational Inputs
• Goal of Models:- High velocity (> 1000 km/s) opening of field
• Inputs:- Slow photospheric driving:-- emergence/submergence of flux-- shear/twist- B-stressing concentrated near Bz reversal line-- B-supports prominences/filaments
Summary of Numerical Models of CMEs
Model
Forbes et al., 1994 Linker, et al. 2001
Chen and Shibata, 2000
Antiochos et al., 1994
Wu et al., 2000
Chen et al., 1997
Pre-Eruption Structure
Flux rope in bipolar field: either emerges or forms in the corona
Flux rope in multipolar field
Sheared arcade in multipolar field
Flux rope with overlying streamer in the solar wind
Flux rope in equilibrium
Pre-eruption Evolution
Flux decrease/changes leading to loss of equilibrium
Flux emerges consistent with reconnection
Continued shearing
Increase in the azimuthal flux or shear of the streamer field
Increase in the azimuthal flux
Pre-eruption Energy Release
None
Reconnection energization at the site of emergence
Reconnection energization at coronal null/separator
None
None
Caution: This table is incomplete, mainly initiation
Homologous CMEs?
• Homologous flares are known: flares from the same region with same morphology and similar light curves.
• Are there homologous CMEs?- multiple CMEs from the same region• Candidate events: transequatorial CMEs
during April 27-May 8, 1998 (http://cdaw.gsfc.nasa.gov)
CMEs and Helicity - Solar Dynamo builds up helicity- Released by CMEs
• Use full-disk MDI magnetograms to calculate global distribution of H (assuming B to be constant over certain time intervals & exploiting the fact that B is seen different directions).
• Compare global helicity distribution and evolution with appearance of CMEs.
• Use vector magnetograms to study helicity and CMEs in active regions in comparison with the helicity of the global B.
“Reconnection-favoring” Flux Emergence
2000/09/12 SXR & H-alpha
Pre-eruption
Post-eruption
Energy Release Near Filament
Filament Eruption in EUV
• SOHO/EIT (195 A) images presented as a movie.
• The NW-SE filament in the southern hemisphere erupts and becomes the core of the white light CME
• Arcade formation follows the eruption
H-alpha:Before and After Eruption
2000/09/12 CME on the Disk
• SOHO/LASCO C3 movie
• Partial halo event consistent with the southern location on the disk
• The bright core is the filament
2000/09/12 CME in LASCO/C2
CMEs and ICMEs:A tentative correspondence
CMEs Near Sun• Shock • Frontal • Cavity • Prominence Core • Arcade Formation
ICMEs near Earth• Shock• Sheath• Ejecta/MC• Pressure Plug• --------------
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