Coronal Mass Ejections without
photospheric/chromospheric
signatures
Session organizers: Alexei Pevtsov (NSO) and Vasyl Yurchyshyn (BBSO)
Discussion leaders: Yuhong Fan (HAO) and Benjamin Lynch (UCB)
“Stealth” CMEs
STEREO-A
LASCO
STEREO B
Robbrecht et al, 2009
Ma et al, 2010
Pevtsov et al 2011
O. Panasenco
It is not “stealth” if I can see it!
-Terminology (“stealth” or “without source region” or better (?)
“CMEs with hard-to-detect on-disk signatures”) – we do see some
changes in low corona if we know what to look for; there is always
a source region, if we know where to look at. Traditionally, we
expect flares, filament eruption, coronal waves and dimmings
associated with CMEs. “Stealth” CMEs do not have these attributes
and so, are harder to detect on the disk. But once they erupt, we
can see them well in higher corona.
Why we should care?
-A small but significant fraction of CMEs comes from
unidentifiable sources (Jie Zhang, major geostorms DST < -100;
1998-2005, 10 out of 88 CMEs had no clear source on the disk).
What are “stealth” CMEs?
• Do they represent a different class of CMEs
(same/different magnetic topology)?
• How common/rare they are? (specific phase
of solar cycle)?
• What makes them different from “regular”
CMEs?
Properties of “stealth” CMEs
-Are typically slow CMEs
-Are more massive than
“typical” CMEs
-More than half of the
“stealth CMEs” show
coronagraph signatures
indicative of the standard
flux rope eruption scenario
Jan 1 through Aug 31,
2009 – 1/3rd of CMEs
are “stealth”
Ma et al, 2010
B. Lynch
Courtesy of T. Berger (LMSAL)
“Stealth” CMEs originate from long high-corona flux ropes
(very stable, slow rising which allows:
 filament material to drain off completely prior to the
eruption) – O. Panasenco observed several cases when
filament channels had emptied prior to “stealth” CMEs
Torus instability to develop (Y. Fan model).
To collect significant amount of mass from streamer belt (M.
Kramar, A. Vourlidas)
“Stealth” CMEs originate from areas of weak magnetic field
(but in a weak field environment, the flux rope may form lower
in atmosphere)
Some CMEs are “stealth” because of limitation of our
observations (not looking at the right wavelength, insufficient
column density to make on-disk features visible etc.
Why we do not see signature of
eruption in low corona?
- “stealth” CMEs do not require
magnetic reconnection (Jie Zhang)
A. Vourlidas
dimming
- If the reconnection rules:
1. if it is a weak field
environment - much less energy is
released
2. bulk of energy goes to kinetic
energy and very little - to particle
acceleration
3. because of the height of the
erupting flux rope, the low corona
signatures are minor (or distant).
no dimming
How about forecasting of “stealth”
CMEs?
“Stealth” CMEs are not driven from below (photosphere/
chromosphere) – potentially could make easier to forecast?
 Flux rope is formed prior to eruption, current sheet is formed
below the flux rope, and filament had drained off – could these
properties be used for forecasting?
 (are we looking in the right place?) shear/stress along the
neutral line or helicity build up in the corona, – could any of these
be useful for forecasting?
Limb observations seems to be essential if the flux rope has the
right orientation (but limb observations of transequatorial “loops”
may give a hint of “stealth” CME configuration).
What is next?
• We need to develop forecasting tools for
“stealth” CMEs based on their properties
• Properties of “stealth” CMEs suggest that they
could be easier to model than “regular” CMEs.
• Case study? Potential candidates: 13 June
2010 (west limb), 12 June 2010 (east limb), 3
Mar 2011?