Another unknown issue of the SW is the origin of slow solar wind

1. Another unknown issue of the SW is the origin of slow solar wind

2. Low-speed wind models Helmet-streamer Blob-loop reconnection Wang et al. (1999) Expanding active region Nakagawa & Uchida

3. Helmet-streamer model N Magnetic neutral sheet S Low-speed wind is associated with a neutral sheet.

4. Slow solar wind from an equatorial coronal hole N Magnetic neutral sheet S

5. potential field neutral line A neutral line does not traverse through the minimum speed locus. after Crooker et al., 1997

6. potential field neutral line ? ? after Kojima et al., 1999

7. potential field neutral line ? ? after Kojima et al., 1999

8. after Kojima et al., 1999

9. after Kojima et al., 1999

10. MHD simulation by Linker & Mikic ’99 V V N low density low speed from coronal hole

11. Hinode Continuous Upflow of Plasmas Sakao et al., 2007

12. after Kojima et al., 1999 Coronal hole model Helmet streamer model

13. Origin of slow SW(seCH) Coronal hole origin but ⇒ extra momentum source in lower corona Large NV High T (in seCH) Enhanced Heating in lower corona seCH StrongB (in seCH)

14. Slow SW from a polar CH

15. dependence on polar coronal hole scale size Slow solar wind from a polar coronal hole 1999 1991 2000 Oct. 1999

16. Small Polar Coronal Hole

18. Polar Low-speed Solar Wind at Solar Activity Maximum of Cycle 22 June 27, 1990 Ohmi et al. [2001]

19. 12G 4～6G 18G slower fast slower slow

20. Very slow solar wind originates from a small coronal hole vicinity of active regions. • When a polar coronal hole becomes very small, it becomes a source of slow solar wind.2.