Unusually low density regions in the compressed slow wind: Solar wind transients of small coronal hole origin

Abstract

We report on two small solar wind transients embedded in the corotating interaction region, characterized by surprisingly lower proton density compared with their surrounding regions. In addition to lower density, these two small solar wind transients showed other interesting features like higher proton temperature, higher alpha-proton ratios, and lower charge states (C+6/C+5 and O+7/O+6). A synthesized picture for event One combining the observations by STEREO B, ACE, and Wind showed that this small solar transient has an independent magnetic field. Back-mapping links the origin of the small solar transient to a small coronal hole on the surface of the Sun. Considering these special features and the back-mapping, we conclude that such small solar wind transients may have originated from a small coronal hole at low latitudes.