sarah gibson

Sarah Gibson January 2006

Sigmoids, filaments and cavities: how do they connect?

Sigmoids, filaments, and cavities are of interest

• because of their observed connections to CMEs

• because they tell us about coronal equilibrium magnetic structures

MOTIVATION:

Brief review

• Observations of sigmoids, filaments, cavities at different stages in their evolution,

• How different magnetic models have been used to explain various aspects of these observations

We then use one particular flux rope model (partially erupting) to explain the whole story, e.g.

• Evolution

• How these different phenomena relate to each other

OUTLINE

1. Filaments

• Cold, dense

• Thin sheets above NL

• Inverse magnetic configuration

• Erupt -- often not completely

BACKGROUND: Observations of sigmoids, filaments, cavities vs. CMEs:

2. Cavities

• Density depletion

• Ubiquitous, associated with filament channel

• Morphology (circular cross-section, elongated tunnels (the ones we see), sharp edge (ditto))

• Long-lived

• Bodily erupt (3 part structure)


3. Sigmoids

• X-ray hot S-shaped loops/patterns

• Quiescent

• Eruptive

• Sigmoid --> cusp

• Reforming sigmoid below cusp


BACKGROUND: How models have explained these observations

1. Filaments

• Cold, dense -- supported by magnetic fields (dips)

• Thin sheets above NL -- sheared (shallow?) dips line up above NL

• Inverse magnetic configuration (flux rope/also Antiochos?)

• Erupt -- often not completely (many models!!! Partial -- where reconnection happens)


2. Cavities

• Density depletion -- high magnetic pressure

• Ubiquitous, assoc. with fil. channels -- flux rope, same magnetic structure as filaments

• Morphology (circular cross-section, elongated tunnels, sharp edge (that we see, anyway)) -- magnetic flux rope

• Long-lived -- thermal isolation

• Bodily erupt (3 part structure) -- pre-existing flux rope eruption


3. Sigmoids

• X-ray hot S-shaped loops/patterns: current sheets, reconnection in general, ohmic?

• Quiescent -- perturbation of BPSS (other?)

• Eruptive -- many models

• Sigmoid --> cusp -- spec. torok, others?

• Reforming sigmoid below cusp -- us --- transition to next section

BEFORE SigmoidDescribed in Fan and Gibson 2006

• Current sheets form during emergence of flux rope

• Along BPSS as predicted: BPSS field lines intersect current sheets towards their base. Bear in mind, true current sheet could extend higher as it would lose its dependence on field strength. And most of the BPSS lines intersect some part of the sigmoid CS. So, would expect heating of whole sigmoid surface.

• Some vertical central sheet also, as there is some kinking/squeezing of legs (see later discussion of sigmoid during eruption)

• described in Gibson et al. 2004)

• borne out for spherical simulation, non-erupting case (Fan and Gibson, 2006)

• Filament sits in the dips of the flux rope (but not necessarily all dips)

• Sigmoid heating in vicinity of BPSS (purple lines): intersect current sheets (orange)

• Relation of quiescent filament/sigmoid matches observations

• Sigmoid middle + all filament along inverse-S shaped neutral line

• Sigmoid ends curve over to bipole maxima

• Sigmoid vs. filament, above or below? Both -- sigmoid middle below, ends above -- projection effects: mostly appear above

BEFORE Sigmoid vs. filament

QuickTime™ and aBMP decompressor

are needed to see this picture.

BEFORE filament (different viewing angles)



• Which dips would fill?

• Not where intersect CS?

• Not where slope too steep?

• higher ones harder to get to?

BEFORE filament (which dips fill?)



• Quiescent case FG06

• Rope almost fully emerged -- bpss almost at boundary

• 3 part

• some necking

BEFORE Cavity +filament



DURING: rope erupts

DURING: current sheets form

As in quiescent case --

• CS form in region of original BPSS (but note BPSS now evolving)

• Also in vertical current sheet (VCS) at center (legs squeeze together)

DURING: topology mixes

1. Reconnections with the overlying arcade mixing the rope and arcade topologies

• Happens at flux rope leg-sheared arcade interface: part of BPSS

• F-F (rope) + A-A (loop) --> F-A (loop) + A-F (rope) (high (concave up) ends rooted in arcade, low (dipped) ends in rope bipole, because the high ends are closest to the rope-arcade interface)

What sort of reconnections occur at these current sheets?

Some are clear-cut, topology-changing reconnections:

2. Reconnection between the rope legs as they are squeezed together as the rope kinks

• F-A (rope) + A-F (rope) --> F-F (rope) remaining + A-A (rope) escaping

DURING: rope breaks in two

Rope breaks in two!

What sort of reconnections occur at these current sheets?

Some are clear-cut, topology-changing reconnections:

• Allows field lines to swap footpoints with neighboring lines (dark blue now has joined with light blue)

• Especially happens at BPSS, where one field line is “stuck” (dark blue) but neighboring field (light blue) just above is free to lift off

3. No change in topology, but footpoint motion ultimately facilitates rope-breaking and rope-arcade-mixing reconnections

DURING: interchange reconnectionsOthers involve multiple reconnections

DURING: sigmoid brighteningSigmoid heating will occur on field lines reconnecting at these current sheets

Initially:

• red lines through central vertical current sheet

• purple lines through leg current sheets (some of t=86 BPSS)

DURING: sigmoid brightening

We would expect reconnection-heated lines to at first appear sigmoid-shaped

DURING: sigmoid vs. filament



These initial sigmoid reconnecting field lines

• lie below filament that escapes (upper brown dips)

• lie either completely above filament that survives (lower brown dips), e.g. lines reconnecting at VCS

• or else wrap around surviving filament at BPSS, in the same manner as the quiescent sigmoid. Note as in that case, arched portion of sigmoid loops lie above filament


At least at first, centrally co-spatial X-ray sigmoid and filament

DURING: filament could break in two






Redo with more complete set of red reconnecting lines?

As eruption progresses

• upper flux rope escapes (upper blue lines -- initially dipped, potentially filament-bearing)

• lower filament settles down and survives (lower brown dips)

• reconnecting field lines go from sigmoid to cusp (red lines)

DURING: sigmoid vs. filamentAs eruption progresses

• upper flux rope escapes (upper blue lines -- initially dipped, potentially filament-bearing)

• lower filament settles down and survives (lower brown dips)

• reconnecting field lines go from sigmoid to cusp (red lines)



Redo with more complete set of red reconnecting lines?

•make a movie of erupting 3 part structure

DURING: Cavity erupts (3 part CME)

Rope has broken in two -- one erupting rope, rooted in arcade, and one remaining rope, rooted in original rope’s bipole. Separated by cusped post-flare loops.

AFTER: partial expulsion of rope

Note there is a smooth transition for the F-F end-state lines, from dipped rope (purple and red) to the tops of the rope (darkest orange) to cusped post-flare loops (lighter orange and yellow)

The final closed down A-A arcade appears here as the outermost black line.

AFTER: partial expulsion of rope

Multiple reconnections with the arcade and within the rope occur, breaking the rope in two, but these reconnections occur above the dipped portions of some field lines where filament mass could be

A significant set of dipped field lines remain in non-erupting portion of flux rope (e.g. red and pink/purple lines)

Some or all of the filament mass (depending which dips were originally filled) could survive the eruption

AFTER: Filament dips survive

Before After

Black line is the line separating dipped from concave up lines

Blue line is rope axis

AFTER: Filament dips survive

Before After

AFTER: lower filament unaffected by eruption



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AFTER: cusp overlying sigmoid

QuickTime™ and aYUV420 codec decompressor


Dimmings: • plot slices of density at base (or integrated along los at base)

• footpoints of erupting cavity

• could also plot footpoints of all open field lines

•Note since escaping flux rope is rooted in arcade, this would explain bigger dimmings than enclosed in sigmoid

AFTER: Cavity/dimmings

sarah gibson

Documents

sigmoid current sheets

magnetic flux ropelong

different magnetic models

emergence of flux rope

bpss lines

cuspreforming sigmoid

sigmoid surface

dips sigmoid heating