1. Data-Driven MHD Modeling of CME Events
Session Summary, day 2
Session Organizers: Yuhong Fan (HAO), George Fisher (SSL/UCB),
Mark Linton (NRL-DC), Brian Welsch (SSL/UCB)

2. Slava Titov: "Structural Analysis of the Coronal Mag-netic Field: How Can It Be Used in Models of CMEs?"
Start: review of separatrix surfaces, and quasi-separatrix layers
(QSLs) as sites of reconnection;
Q := "squashing factor" quantifies rate of change of field-line connectivity near a QSL
Q enables:
localising preferred sites of reconnection, i.e., quasi-separators
identifying building blocks, e.g., erupting and non- strands of flux ropes
(3) determine evolving fluxes for each blocks
(4) relate observable structures to building blocks:
H-alpha flare ribbons,
EUV dimmings,
X-ray sigmoids

3. Relation to observational features
t=32 (≈ 38 min after the CME onset)
The ribbons propagate outward from the PIL by increasing in length.
The area of dimmings (footprints of erupting FR) quickly expands and then disappears.

5. Roussev: Use Dynamic Flux Emergence Simulations (w/Galsgaard & Archontis) to Drive Coronal Model
This enables driving with more self-consistent boundary conditions.
- required rescaling β from photospheric to coronal values, and decreasing peak field strength.
Flux rope forms, and erupts; post-eruption field consists of two flux ropes, which form a “double J” structure
synthetic X-ray emission resembles observed sigmoids
Topology matters: nulls & QSLs play important roles (cf., Titov)
Footpoints of erupting rope do not remain stationary, but move across surface as eruption proceeds.
Flux rope does not remain intact: after eruption, two flux ropes are formed, linking “core" of emerged field to external field

6. Magnetic Field Geometry at Early Times
t = 68 min
Reconnection becomes increasingly complicated as flux rope emergence proceeds.
Magnetic flux and helicity continuously leave the flux emergence region via sequence of reconnection events.
Newly formed field lines posses fair amount of twist and writhe due to transfer of mutual helicity (prior to reconnection) to self-helicity (after reconnection).

7. Magnetic Field Geometry at Later Times
t = 3 h
Two confined flux ropes left in low corona have one footprint coinciding with footprint of original flux rope, and another footprint located well outside flux emergence region.
Electric current and plasma temperature very high along each flux-rope channel!
Strong soft X-ray emission (double-J shape) comes from regions occupied by two flux ropes, as well as region in between.

8. Magnetic Field Geometry at Later Times
t = 68 min
t = 3 h

9. Several “data inspired” simulations of actual eruptions were presented: Zuccarello; Fan; Jin.
Models had varying degrees of thermodynamic realism.
Fan’s CME was slower than the observed CME:
Fan: Rescaling must preserve height profile of B.
Fisher: If you get a 1000 km/sec eruption, how do you change parameters to achieve a 2000 km/sec eruption?
Mikic: To increase eruption energy, confine the pre-eruption field more strongly.
Fisher: So, for instance, if you want to build a pipe bomb, you should not use a cardboard tube, you should instead use a metal tube.
Mikic: Yes, you want to prevent expansion for a while…
Meng Jin studied a CME shock with one-T and two-T models:
1T: 9 MK precursor far ahead of shock
2T: 3 MK peak e- T, 100 MK peak proton T (Mach #’s near 4)
Heat flux saturation (not in model) was discussed

10. Reinard: Charge-state predictions from MHD CME simulations can be used to interpret in situ observations.
QFe derived from Breakout model
QFe derived from Flux cancellation
QFe observations for the two May 19-21, 2007 MCs
MC2
MC1
STA
ACE
STB