No Trace Left Behind: Stereo Observation of a Coronal Mass Ejection
  without Low Coronal Signatures
  The availability of high quality synoptic observations of the EUV and visible
corona during the SOHO mission has advanced our understanding of the low corona
manifestations of CMEs. The EUV imager/white light coronagraph connection has
been proven so powerful, it is routinely assumed that if no EUV signatures are
present when a CME is observed by a coronagraph, then the event must originate
behind the visible limb. This assumption carries strong implications for space
weather forecasting but has not been put to the test. This paper presents the
first detailed analysis of a frontside, large-scale CME that has no obvious
counterparts in the low corona. The event was observed by the SECCHI
instruments. The COR2A coronagraph observed a slow flux-rope type CME, while an
extremely faint partial halo was observed in COR2B. The event evolved very
slowly and is typical of the streamer-blowout CME class. EUVI A 171 images show
a concave feature above the east limb, relatively stable for about two days
before the eruption, when it rises into the coronagraphic fields and develops
into the core of the CME. None of the typical low corona signatures of a CME
were observed in the EUVI-B images, which we attribute to the unusually large
height from which the flux-rope lifted off. This interpretation is supported by
the CME mass measurements and estimates of the expected EUV dimming intensity.
Only thanks to the availability of the two viewpoints we were able to identify
the likely source region. The event originated along a neutral line over the
quiet sun. No active regions were present anywhere on the visible (from STEREO
B) face of the disk. Leaving no trace behind on the solar disk, this
observation shows unambiguously that a CME eruption does not need to have clear
on-disk signatures.
