The Origin and Development of the May 1997 Magnetic Cloud
David Webb Submitted: 2000-08-28 16:00
A complete halo coronal mass ejection (CME) was observed by the SOHO LASCO
coronagraphs on May 12, 1997. It was associated with activity near Sun center,
implying that it was aimed Earthward. Three days later on May 15 an interplanet-
interplanetary shock and magnetic cloud/flux rope transient was detected at the
WIND spacecraft 190 Re upstream of Earth. The long enduring southward magnetic
fields associated with these structures triggered a geomagnetic storm. The CME
was associated with a small coronal arcade that formed over a filament eruption
with expanding double ribbons in Hα emission. The flare was accompanied by
a circular EUV wave, and the arcade was flanked by adjacent dimming regions. We
surmize that these latter regions marked the feet of a flux rope that expanded
Earthward into the solar wind and was observed as the magnetic cloud at Wind. To
test this hypothesis we determined key parameters of the solar structures on May
12 and compared them with the modeled flux rope parameters at Wind on May 15.
The measurements are consistent with the flux rope originating in a large
coronal structure linked to the erupting filament, with the opposite-polarity
feet of the rope terminating in the depleted regions. However, bidirectional
electron streaming was NOT observed within the cloud itself, suggesting that
there is not always a good correspondence between such flows and ejecta.
Authors: D.F. Webb, R.P. Lepping, L. Burlaga, C. DeForest, D. Larson, S. Martin, S.P. Plunkett, and D.M. Rust.
Publication Status: JGR, Vol. 105 , No. A12 , 27,261
Last Modified: 2000-12-08 12:57