Dark energy in the solar corona
• Not the "dark energy" of the cosmos, but B!
• MHD equilibrium
• Imperturbable compact event
• Imperturbable cusp
• Two CMEs
• Blow-out of LPS
The open fraction of coronal field lines (v. roughly the area of the coronal holes) remains approximately constant
A. There isn't much braiding observed in quiet-Sun magnetic fields (K. Schrijver, 2001)
B. Predictions of the solar wind are happy with a “potentialfield” source-surface model
REMARKS
C. So how does “energy build-up” happen?
Imperturbability on a compact scale
Flares often involve multiple loops that don’t appear to touch.
One loop brightening (pressure pulse) usually doesn’t affect its neighbors geometrically.
Sorry not to have any good examples readily at hand.
Imperturbability on a large scale
The same principle applies - often the distant corona ignores what looks to us like a titanic explosion.
Excellent example from June 6-7, 2000 (see APOD).
Photosphere
“SourceSurface”
Solar wind: radial field lines
Corona: force-free field
Minimal model for a CME: initial conditions
Minimal model of a CME
• A force-free coronal equilibrium interfaces to a radial field in the solar wind, initially.
• A flare happens and a CME opens a large new swathe of field lines.
• The MHD equilibrium prior should adjust to a new equilibrium state outside the CME.
• We don’t see this happening.
How “massive” is the corona?
1. Total magnetic energy = 1034 ergs, hence a major CME is a 1% effect.
2. A major CME occupies 1 steradian hence a major CME is a 10% effect.
3. In any case there should be a local effect on the equilibrium.
Inferences
• The solar-wind structures resulting from a CME may have little to do with the coronal structure causing it.
• The energy involved is hard to trace, because the dominant term is the coronal B field, especially if it is low
Dark energy in the solar corona
• Apparently great perturbations can occur without disrupting the basic equilibrium of the corona.
• Great perturbations often do not permanently displace nearby coronal structures.
• Extremely different solar perturbations can cause nearly identical ICMEs.
• The bottom line: coronal MHD equilibrium is not easy to understand intuitively.
Once again, I’ve managed to give atalk, the main point of which is thatI don’t understand what is going on...