We briefly describe the "standard model" for the production of coronal mass ejections (CMEs), and our view of how it works. We then summarize pertinent recent results that we have found from SOHO observations of CMEs and the flares at the sources of these magnetic explosions. These results support our interpretation of the standard model: a CME is basically a self-propelled magnetic bubble, a low-beta plasmoitl, that (1) is built and unleashed by the tether-cutting reconnection that builds and heats the coronal flare arcade, (2) can explode from a flare site that is far from centered under the full-blown CME in the outer corona, and (3) drives itself out into the solar wind by pushing on the surrounding coronal magnetic field

Moore, Ronald L.

Seuss, Steven T.

Sterling, Alphonse C.

NASA Technical Reports Server

MSFC- 531
Conference Book Title
ASP Conference Series, Vol. XXX, YEAR
Editor 1, Editor 2 and Editor 3, eds.
New Evidence that CMEs are Self-Propelled Magnetic
Bubbles
Ronald L. Moore1 , Alphonse C. Sterling1,2 and Steven T. Suess1
1NASA/MSFC, VP62, Huntsville, AL 35812, USA
2 JAXA/ISAS, Hinode Group, 3"1"1 Yoshinodi, Sagamihara, Kanagawa
229"8510, Japan
Abstract.
We briefly describe the "standard model" for the production of coronal
mass ejections (CMEs), and our view of how it works. We then summarize
pertinent recent results that we have found from SOHO observations of CMEs
and the flares at the sources of these magnetic explosions. These results support
our interpretation of the standard model: a CME is basically a self~propelled
magnetic bubble, a low-beta plasmoitl, that (1) is built and unleashed by the
tether-cutting reconnection that builds and heats the coronal flare arcade, (2)
can explode from a flare site that is far from centered under the full-blown CME
in the outer corona, and (3) drives itself out into the solar wind by pushing on
the surrounding coronal magnetic field.
1. The Standard Model for CME Production
The scenario for CME production that is now often referred to as the "standard
model" is presented in detail in Moore & Sterling (2006). This is the picture for
ejective solar eruptions that was first put forth by Hirayama (1974) and has been
modified and further supported by many subsequent observational and modeling
studies (e.g., Kopp & Pneuman 1976; Heyvaerts et al 1977; Moore & LaBonte
1980; Sturrock et al 1984; Moore & Roumeliotis 1992; Shibata et al 1995; Rust
& Kumar 1996; Moore et al1997; Antiochos 1998; Shibata 1998; Antiochos et al
1999; Canfield et al1999; Forbes 2000; Roussev et al 2003; Qiu et al 2004; Gibson
et al 2004, 2006; Rust & LaBonte 2005; Wang 2006). In the present-day version
of the standard model (e.g., Fig. 1 of Moore & Sterling 2006), the source of a
CME, before it explodes, is a closed bipolar magnetic arcade, in which the core
field, the field rooted near the polarity inversion line, is strongly sheared and
twisted and is partly a sigmoidal flux rope. Dictated by specifics of the configu-
ration and evolution of the field in and around the sheared-core arcade, eruption
of the sigmoidal core field can be initiated via: internal tether-cutting reconnec-
tion·and/or external tether-cutting reconnection (breakout reconnection) and/or
MHD instability. Whether or not internal tether-cutting reconnection is part of
the eruption onset process, it is soon strongly driven between opposite-polarity
stretched legs of the core field where they implode against each other below the
erupting flux rope. This reconnection adds magnetic flux to the erupting flux
rope above it and simultaneously adds an equal amount of flux to the growing
ftal'e arcade below it. The growing flux-rope "plasmoid with legs" explodes into
1
https://ntrs.nasa.gov/search.jsp?R=20080003846 2019-08-30T02:12:42+00:00Z
2 R.L. Moore et a1
Figure 1. Schematic depiction of the stemming of the nearly radial magnetic
field of the outer corona from non-radial fields of the inner corona, and the
consequent over-and-olltprogression of a CME that explodes from a suitably
located source region.
the outer corona as the interior of the CME. The whole CME explosion is driven
by the magnetic pressure of its flux-rope-plasmoid interior, which is built and
unleashed by the tether-cutting reconnection, and which drives the CME out
into the solar wind by pushing against the ambient coronal magnetic field.
Evidence that CMEs are driven by their magnetic pressure was pointed
out before Yohkoh (Moore 1998a,b). As was anticipated (Moore 1991), Yohkoh
X-ray movies of sigmoid eruptions verified that sheared-core arcades erupt ac-
cording to the standard model (Sterling et al 2000; Moore et al 2001). We
have found new evidence from SOHO that CMEs are driven by their magnetic
pressure (Moore et al 2007).
2. New Observations Explained by the Standard Model
Our recent studies of CME explosions observed by SOHO indicate that whether
an explosion of a sheared-core arcade produces a CME, and if it does, whether
the CME explodes nearly radially outward from its source or instead is an "over-
and-out" CME like that sketched in Figure 1, depend as much on the strength
and arrangement of the largr~scalemagnetic field in which the exploding arcade
is embedded as on the size and field strength of the exploding arcade.
In Bemporad et al (2005), we reported a particular variety of over-and-out
CME that we call "streamer puffs." From the observations, we inferred that a
streamer-puff CME is driven by the magnetic pressure of a flux-rope plasmoid
that explodes from a compact sheared-core arcade embedded in one foot of an
outer loop of the large magnetic arcade that forms the base of a coronal streamer.
The exploding plasmoid is guided up the leg of the large loop by the field of the
streamer arcade, but has enough magnetic pressure to blowout the top of the
CMEs: Self-Propelled Magnetic Bubbles 3
loop, thereby producing a streamer-puff CME that travels out along the radial
path of the streamer. Moore et ill (2007) reported a streamer~puff CME that was
driven by an exceptionally strong explosion of a compact sheared-core arcade
in a foot of the blown-out loop of the streamer arcade. In this event, strong
coronal dimming occurred in the remote non-flare foot of the blown-out loop,
confirming the Bemporad et al (2005) magnetic-arch-blowout scenario for the
production of streamer-puff over-and-out CMEs. This scenario is a version of
the standard model (see Moore et al 2007).
The observed production of streamer-puff CMEs suggested to us that when
any CME-producing flux-rope plasmoid explodes from a sheared-core arcade, its
pressure, which is nearly all magnetic, exceeds the surrounding coronal pressure,
which is also mostly magnetic. In Moore et al (2007) we therefore surmised that
as the flux-rope plasmoid erupts out through the corona it expands laterally un-
til it achieves lateral pressure balance with the surrounding corona. The lateral
pressure balance of the CME with the coronal field beyond 2~3 Rsun , which
is nearly radial (as in Fig. 1), results in the CME attaining a final constant
heliocentric angular width, 8CME, in the outer corona. This, and the impli-
cation of the standard model that the magnetic flux content of the full-blown
CME is roughly the same as that in the full-grown flare arcade produced by
the same reconnection that builds the CME plasmoid, yield the following sim-
ple approximate equation that can be tested by measuring 8CME of an observed
CME in the outer corona and measuring the heliocentric angular width 8 Flare of
the full-grown co-produced flare arcade: BFlare;:::j 1.4(8cl'vIE/8Flare)2 G, where
BFlare is the flare-site field strength required if the standard model is essentially
the right physical picture for CME production. The coefficient 1.4 in this equa-
tion is set by the strength of the radial magnetic field in the outer corona, which
we estimated by extrapolation from the radial component of the interplanetary
magnetic field mea.'3ured by Ulysses.
Table 1: Test Results
CME Source ElCME 8Ftare Rqrd Rqrd BFtar" Source
(date) Region (deg) (deg) BFlare Fits Region(Gauss) Source Mag.
Region? Energy**
(Yes/No) (ergs)
2002 Centered on
May 20 small 41 2.2 ;:::j 490 Yes rv 1032
15 spot
1999 QR
Feb 9 filament 64 27 ;:::j8 Yes rv 1032
arcade
2003 Centered on
Nov 4 giant 128 8.7 ;:::j 300 Yes rv 1033
15 spot
* Required BFlare ;:::j 1.4(8cl'vIE/8Flare)2 Gauss
** Source Region IVlagnetic Energy == (B2/8-rr) (8FlareRSun)3
In Moore et al (2007), we tested this equation against three well-observed
CMEs that exploded from radically different source regions. For each event, the
4 R.L. Moore et a1
equation gave a value of BFlare that was appropriate for the magnetic setting of
the source of the CME explosion, and was strong enough for the pre-eruption
sheared-core arcade to have had ample free magnetic energy to have produced
the explosion (see Table 1). This positive test indicates that the standard model
is essentially the correct picture for CME explosions, and that a CME is basically
a magnetic bubble that drives itself out into the solar wind by pushing on the
surrounding coronal magnetic field (Moore & Sterling 2006; Moore et al 2007).
Acknowledgments. This wQrk was funded by the Heliophysics Division of NASA's
Science Mission Directorate.
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New Evidence that CMEs are Self-Propelled Magnetic Bubbles

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