Evidences for Low-speed Streams from Small Coronal Hole

Abstract

Using the WIND spacecraft data, we have studied properties of the locally bunched low‐speed stream which was found in association with active regions by tomographic analysis of interplanetary scintillation observations. The source region of this low‐speed stream was inferred to be a small coronal hole at vicinity of active regions by tracing potential magnetic field lines. The following WIND spacecraft observations support this inference of coronal hole origin. (1) Observed magnetic fields have properties of coronal hole origin: IMF polarity is the same as that of the coronal hole, and a magnetic neutral sheet was not observed in the stream. (2) Variations of velocity and density in the stream are as steady and uniform as those in typical high‐speed wind. In addition, we have found that the relative He abundance Nα/NP in this low‐speed stream has 0.032, which is more than two times higher than that in low‐speed wind in the heliospheric plasma sheet (0.013) and very near to that of high‐speed wind from the large coronal hole (0.040). However, proton mass flux density and freeze‐in temperature from the ratio of O7+/O6+ are about 1.5 times higher than those in the coronal hole high‐speed streams. These results imply that the low‐speed steam is originated from a small coronal hole with high mass flux density and is strongly heated in the lower corona.