Dark Energy in the Solar Corona

1
Dark Energy in the Solar Corona

• H.S. Hudson, UCB SPRC

LMSAL, January 31, 2002
2
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

3
The corona is surprisingly stable. What is
the nature of this equilibrium?
4
The corona exhibits a "stick-slip" variability,
as shown on any GOES plot
5
The open fraction of coronal field lines (v.
roughly the area of the coronal holes) remains
approximately constant
6
REMARKS
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
potential field source-surface model
C. So how does energy build-up happen?
7
Imperturbability on a compact scale
Flares often involve multiple loops that dont
appear to touch. One loop brightening (pressure
pulse) usually doesnt affect its neighbors
geometrically. Sorry not to have any good
examples readily at hand.
8
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).
9
A beautiful coronal cusp resulting from a
flare/CME on June 6, 2000
10
The GOES time history for June 6-7, 2000
11
Oooops
Before After
12
100 DN
500 DN
153623 minus 145227 UT
Remember the movie!
13
Measurement results
Measurement geometry
14
Solar wind radial field lines
Source Surface
Corona force-free field
Photosphere
Minimal model for a CME initial
conditions
15
Radial field
Source Surface
FF
FF
Photosphere
Minimal model for a CME a flare has
happened!
16
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 dont see this happening.

17
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.
18
Seemingly identical interplanetary CMEs can have
very different coronal origins.
19
Impulsive flare North of equator Filament Dimming
Giant arcade South of equator Filament No dimming
20
Ulysses ICME observations (Gosling et al., 1994)
1
2
21
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 b.

22
An exception to prove the rulethe disruption of
a post-flarearcade - v. unusual
23
FFIs first...
24
(No Transcript)
25
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.

26
Once again, Ive managed to give a talk, the main
point of which is that I dont understand what is
going on...
27
(No Transcript)