Our knowledge about slow solar wind (~400 km/s) and especially its origin is very limited. Theoretical models suggest that coronal holes boundaries (CHBs) are the main source of the slow solar wind. The helmet-streamer loops are also considered as a possible source but with the major component still coming from the CHBs.
Because of the different rotational profiles in the corona and at photospheric level and the fact that coronal hole boundaries separate two topologically different magnetic field configurations, CHBs are presumably the region where a continuous opening and closing of magnetic field lines takes place. This reconfiguration is believed to happen through magnetic reconnection between
the open magnetic flux of the coronal hole and the closed one of the quiet Sun.
Madjarska, Doyle & van Driel-Gesztelyi (2004, ApJ, 603, 57) found the first evidence for magnetic reconnection along coronal hole boundaries using SUMER observations in spectral lines formed at transition region temperatures. This suggests that low lying loops which are abundant along CHBs are continuously evolving and reconnecting with the open magnetic flux of the coronal holes as predicted recently by Fisk (2005, ApJ, 626, 563).
Therefore, simultaneous spectroscopic, imager and magnetic field data are need to further explore this problem.
We already performed some equatorial coronal hole boundaries observations which are presently analysed. The analysis shows that it is of great importance to
have the same observations made in the quiet Sun and at polar coronal hole boundaries.
The EIS studies were modified to meet the new telemetry constrains.
Simultaneous observations with TRACE (in the UV channels so it can be run during the eclipse period) and MDI (while at disk center) will be requested as soon as Hinode decides on the dates and time slots. |
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