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Discovery of Bi-directional Jets at Coronal Hole Boundaries

Gerry Doyle reports that collaborative research with Maria Madjarska has revealed for the first time the presence of bi-directional jets and magnetic reconnection occurring at coronal hole boundaries. The SUMER observations obtained in NeVIII 770.42Å (6 x 10⁵K) and NIV 765.15Å ( 1.3 x 10⁵K) show small regions of a few arcsec size with strong blue- and red-shifted emission reaching Doppler shifts up to 150km s^-1 which are associated with bi-directional jets. The jets occur at coronal hole boundaries where evolving loop systems are present. Data from quiet-Sun regions obtained a few hours later on the same day with the same observing programme were used to compare the occurrence rate of bi-directional jets in such regions to those along coronal hole boundaries. We found that the number density of jets at the coronal hole boundaries is one order of magnitude higher than in the quiet Sun region. The role of such events in the evolution of the coronal hole boundaries is an important topic for further research.

Figure 5: The triangles show the positions of the bi-directional jets: reversed colour intensity image in NIV 765.15Å (left panel); Doppler shift map obtained by applying a single Gaussian fit from -30 to +30km s^-1 (middle panel); and reversed colour EIT FeXII 195Å image (right panel).