Low‐speed solar wind from the vicinity of solar active regions

Abstract

We have investigated the origin of low‐speed winds observed in association with active regions near the equator at times of solar activity minimum. The solar wind velocity distribution on a source surface at 2.5 R s is derived by interplanetary scintillation tomographic analysis, and compact low‐speed regions in it are investigated in relation to active regions and large‐flux‐expansion regions. We show that although the low‐speed regions tend to be located near active regions, they are more closely associated with large flux expansion from the vicinity of active regions. We find that slow solar wind does not arise from closed magnetic loops above an active region, but instead the low‐speed stream originates from the vicinity of one polarity side of the active region. Therefore the low‐speed stream, unlike the helmet streamer, has a single magnetic polarity. This can explain why compact low‐speed streams are often not associated with a heliospheric current sheet.