Locating the solar source of 13 April 2006 Magnetic Cloud

1. Locating the solar source of 13 April 2006 Magnetic Cloud K. Steed1, C. J. Owen1, L. K. Harra1, L. M. Green1, S. Dasso2, A. P. Walsh1, P. Démoulin3 and L. Van Driel-Gesztelyi1,3,4 1UCL - Mullard Space Science Laboratory 2University of Buenos Aires, Argentina 3Observatoire de Paris, France 4Konkoly University, Budapest, Hungary

2. 13 April 2006 MC: Observational Evidence • Forward fast shock • Sheath • ICME ejecta • - MC: ~16:00 UT (13 April 2006) – 01:15 UT (14 April 2006) • - Enhanced B • - Decrease in variability of B • - Smooth, coherent rotation of Bx, By and Bz • - Bipolar signature in By • - Low proton temp • - counterstreaming, suprathermal electrons • Duration ~ 9 hrs |B| nT Counterstreaming electrons Bx nT By nT Bz nT Proton Density #/cc SW Speed km/s Proton Temp Kelvin The magnetic cloud is LEFT-HANDED negative sign of helicity 0 0.5 1.0 1.5 2.0 2.5 3.0 Time after 12:00 UT 12 Apr 2006

3. Launch Window: 9 – 11 April 2006 - average measured speed of ejecta at 1 AU: ~ 520 km/s - distance travelled: ~ 1 AU - calculated propagation time: 80 h - calculated launch time: 12:00 UT 10 April 2006 - allows for acceleration/deceleration of the ejecta as it propagates away from the Sun No obvious CME signatures - flares, dimmings, etc. - makes the source region of the magnetic cloud more difficult to determine Locating the Solar Source of the Ejecta

4. At 12:00 UT 10 April 2006 (estimated launch time): 0869 0866 0867 Survey of Possible Source Regions 0871 • Three active regions on the limb, one active region on the disk • ALSO: Small northern hemisphere active region emerges • - not large enough to develop sunspots or be allocated a NOAA AR • number • An EUV brightening is observed at 05:47 UT 10 April 2006 in AR10869 at 195 Å (T = 1.5 x 106 K) AR10869: possible solar source of the ICME?

5. Magnetic helicity signs of possible source regions - magnetic “tongues” - For positive twist, the leading polarity appears elongated and extends southward of the following polarity. The mirror image is true for a negative sign of twist. - A positive twist is expected in southern hemisphere ARs like AR10869 Other Association Criteria • Leading polarity (negative) flux emerges along the southern side of the following (positive) polarity flux positive sign of helicity (right-handed) • Within the launch window, it was found that only the small, northern hemisphere active region was likely to have a negative sign of helicity (left-handed) • The leading (positive) polarity extends northward of the following (negative)polarity during the early emergence phase negative sign of helicity

6. Disappearing Filaments • A number of active region and quiescent filaments are observed in Hα within the launch window • One quiet Sun filament is located in the northern hemisphere (which is expected to have a negative sign of helicity) • - this filament is NOT seen to erupt within the launch window! • Coronagraph Observations • A faint, partial halo CME was observed at ~06:00 UT 10 April 2006 by LASCO • - extending towards the south west • - linear speed ~ 183 km/s • - estimated onset time ~ 04:00 UT 10 April 2006 Locating the Solar Source A lack of eruption signatures on the disk corresponding to this CME have led us to conclude that this was a BACK-SIDED EVENT • This is the only halo/partial halo CME recorded in the LASCO CME catalog within the launch window – also independently verified

7. At ~ 09:30 UT 11 April 2006: - a cusp is observed by EIT (195 Å) - formation of post- eruption loops is observed by TRACE (171 Å) SOLAR SOURCE: Northern Hemisphere AR Cusp-shaped coronal loops signature of eruption Cusp • AR is situated on the boundary of a coronal hole • - expected to erupt more readily than if it • were situated in the quiet Sun

8. LOCATION: eruption occurs close to disk centre TIMING: eruption occurs within the expected launch window SIGN OF HELICITY: the magnetic helicity sign of the magnetic cloud and the solar source are in agreement Linking the Coronal Eruption and the MC • It is predicted that the ACE spacecraft crossed the western leg of the MC, in agreement with the eastern position of the source region with respect to the central meridian • The magnitude of the FLUX within the magnetic cloud does not exceed the calculated flux within the active region • The location of the source region near to the central meridian at the time of the eruption, together with its close proximity to a coronal hole explains the presence of a high speed solar wind stream following the magnetic cloud

9. A magnetic cloud was observed by ACE on 13 April 2006 • Solar source: an eruption from a small, northern hemisphere active region at ~ 09.30 UT on 11 April 2006 • A number of pieces of evidence link the coronal eruption and this magnetic cloud: • - location • - timing • - sign of helicity • - spacecraft trajectory through the flux rope • - flux • - high speed solar wind flow following the MC • 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. SUMMARY