Polar low‐speed solar wind reappeared at the solar activity maximum of cycle 23

Abstract

The heliospheric tomography of the interplanetary scintillation (IPS) showed that low‐speed (≤350 km s−1) solar wind reappeared at the polar regions during the solar activity maximum of cycle 23. Comparing the distribution of solar wind velocity with the computed coronal magnetic structures, we found that the polar‐low speed streams at the north polar regions appeared just before the polar open fields were about to disappear. The actual existence of the calculated polar open fields was confirmed in the coronal hole maps from the He I 10830 Å absorption line, 195 Å Fe XII emission line, and white‐light images. This situation is very similar to the polar low‐speed streams observed at the previous solar activity maximum of cycle 22.