Prominence material identified in magnetic cloud

Abstract

Coronal mass ejections (CMEs) often appear in coronagraph images as three‐part structures composed of a leading bright front, a dark cavity and a bright core, which are believed to be associated with the sheath of compressed solar wind, the erupting magnetic flux rope and the cool and dense prominence plasma, respectively. However, a convincing identification of this three‐part structure in the in‐situ solar wind is extremely rare. Therefore, there still remains an open question as to what kind of signatures these three CME parts will reveal in the in situ data ([5]). Our work presents a clear identification of prominence material from in situ observations of the solar wind magnetic field and plasma parameters. The Helios 2 solar probe detected a magnetic cloud at 0.5 AU on 30 March 1976. In this event, we found a region with lower proton temperature and higher proton number density than outside, which is consistent with key features of a prominence as cold and dense solar material. During the same time we also found the occurrence of what possibly is He+, which is a special ion expected to occur only in prominence ejecta. Furthermore, the above observations were all made at a location related to the turning point of a bipolar structure of the interplanetary magnetic field, which is coincident with the notion that a solar prominence lies under the magnetic field lines of a bipolar region and is oriented along the neutral line. Furthermore, from our analysis of solar wind velocity distribution functions (VDFs) we can confirm by kinetic evidence that the plasma inside this special region is colder and more isotropic than outside. Above all, our observations circumstantially confirm the 3‐part CME model as described in references [10] and [7].