How small can an interplanetary magnetic cloud source-region be?

MANDRINI, C.H.; POHJOLAINEN, S.; DASSO, S.; GREEN, L.M.; DÉMOULIN, P.; VAN DRIEL-GESZTELYI, L.; FOLEY, C.; COPPERWHEAT, C.

París

Congreso; 35th COSPAR Scientific Assembly; 2004

COPAR

Using multi-instrument and multi-wavelength observations (SOHO/MDI and EIT, TRACE and Yohkoh/SXT), as well as computing the coronal magnetic field of a tiny bipole combined with modelling of WIND in situ data, we provide evidence for the smallest sigmoid eruption - CME - interplanetary magnetic cloud event ever observed. The tiny bipole, which was observed very close to the solar disc centre, had 100 times less flux than an average active region (AR). In the corona it had a sigmoidal structure and we detected a very high level of twist. On 11 May 1998, at about 8 UT, the sigmoid underwent eruption evidenced by expanding elongated EUV loops, dimmings and formation of a cusp. The WIND spacecraft detected 4.5 days later one of the smallest magnetic clouds (MC) ever identified (100 times less flux and radius than an average MC). The link between the sigmoidal EUV bright point eruption and the interplanetary magnetic cloud is supported by several pieces of evidence: good timing, same coronal loop and MC orientation relative to the ecliptic, same magnetic field direction and magnetic helicity sign in the coronal loops and in the MC, comparable magnetic flux measured in the dimming regions and in the interplanetary MC and, most importantly, the pre- to post-event change of magnetic helicity in the solar corona is found to be similar to the helicity content of the cloud, when assuming a length compatible with the fact that thecloud can be dettached from the Sun one day after its ejection. These observations are a challenge to present theoretical CME models, and show us the need of missions such us Solar B and Stereo to contribute to our understandig of the broad spectrum covered by solar eruptive phenomena.