Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh23b1638s&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH23B-1638
Other
2111 Ejecta, Driver Gases, And Magnetic Clouds, 7513 Coronal Mass Ejections (2101), 7526 Magnetic Reconnection (2723, 7835)
Scientific paper
Using ACE in situ data we identify and describe an interplanetary magnetic cloud (MC) observed near Earth on 13 April 2006. We also use multi-instrument and multi-wavelength observations from SOHO, TRACE and ground-based solar observatories to determine the solar source of this magnetic cloud. A launch window for the MC between 9 and 11 April 2006 was estimated from the propagation time of the ejecta observed near Earth. A number of large active regions were present on the Sun during this period, which were initially considered to be the most likely candidate source regions of the MC. However, it was determined that the solar source of the MC was a small, spotless active region observed in the Northern Hemisphere. Following an eruption from this region on 11 April 2006, the ACE spacecraft detected, 59 h later, the passage of the MC, preceded by the arrival of a weak, forward fast shock. The link between the eruption in this active region and the interplanetary MC is supported by several pieces of evidence, including the location of the solar source near to the disk centre and to the east of the central meridian (in agreement with the spacecraft trajectory through the western leg of the magnetic cloud), the propagation time of the ejecta, the agreement between the amount of flux in the magnetic cloud and in the active region, and the agreement between the signs of helicity of the magnetic cloud and the active region (which differs from the sign of helicity of each of the other active regions on the Sun at this time). In addition, the active region is located on the boundary of a coronal hole, and a high speed solar wind stream originating from this region is observed near Earth shortly after the passage of the magnetic cloud. This event highlights the complexities associated with locating the solar source of an ICME observed near Earth, and serves to emphasise that it is the combination of a number of physical characteristics and signatures that is important for successfully tying together the Earth-end and the Sun-end of an event. Further investigation of this MC has revealed some sub-structure towards its centre, observed as a small scale reversal of the azimuthal magnetic field of the MC, similar to that reported by Dasso et al., 2007. We explore several possible explanations for this signature, including the occurrence of multiple flux ropes and/or warping of the magnetic cloud. We also consider whether magnetic reconnection plays a role in creating the geometry that would explain these observations.
Dasso Sergio
Démoulin Pascal
Green Lucie M.
Harra Louise K.
Owen Christopher J.
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