Scientific justification: 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 (open and closed), coronal hole boundaries 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. Wang & Sheely (2004, ApJ, 1196),
however, believe that the reconnection takes place very high in the solar atmosphere (~ 2.5R), and that it occurs continuously in the form of small, stepwise displacements of field lines. A very important part of the present research will be the search for the origin of the slow solar wind. The helmet-streamer loops are considered as a possible source of the slow solar wind but with the major component coming from the coronal hole boundaries. With this present study, we want to observe equatorial coronal hole boundaries in order to find spectroscopic signatures of the physical processes which take place using simultaneously SUMER/EIS observations which will permit observations in spectral lines covering a large temperature range (from 40 000 K to a few million degrees). TRACE and XRT/Hinode will provide high resolution imaging in EUV and X-ray, respectively. MDI and SOT magnetic field data are crucial for this study. The study will combine spectroscopy and imaging and thanks to the high resolution vector magnetograms we can derive the geometry and the 3D scaling via magnetic field extrapolation (Wiegelmann, 2004, Solar Phys. 219, 87). The STEREO EUV and
coronagraph observations will provide the necessary observational material for
studying the connection between the coronal hole boundaries evolution and the slow solar wind generation.
Target - equatorial coronal hole boundaries at three consecutive positions: at
disk center, W40-W50 degrees and limb. Additionally quiet Sun region observations before or after in order to be used as a reference.
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