Plasma jets, observed as X‐ray jets with Hinode XRT telescope (Cirtain et al. 2007), UV jets (Brueckner & Bartoe 1983; Alexander & Fletcher 1999) and chromospheric jets (SOT Ca II H spectral line, Katsukawa et al., 2007; Shibata et al. 2007) are thought to be a manifestation of reconnection process in the solar atmosphere. The fundamental physical parameters of Hinode X‐ray jets are presented in (Savcheva et al. 2007). At present, the XRT jets were identified and described only in polar coronal holes. It is suggested that the occurrence of jets depends on the reconnection of an emerging magnetic bi‐poles with a system of open magnetic field lines. Since quiet sun regions predominantly hosts closed magnetic loops (although open field lines could be present, too) it is expected that X‐ray jets may be less frequent here. Besides, because of their week X‐ray emission and relatively small size, X‐ray jets may be difficult to distinguish against bright disk background of quiet sun areas.
We suggest that events, associated with XRT jets, could be also observed on the solar disk as a bright loops with cusps or loops with blobs (as shown in figure on the left. Image credit: NASA). The pointy shape of those loops suggests that they may be associated with reconnection and/or open (extended) field lines. We propose to consider spiky loops and cusps as an indication of a reconnection between a bi‐pole and the open field and, therefore, jets may be present at one end of a flaring loop (Canfield et al. 1996). Also, it is not excluded that quiet sun areas outside coronal holes may as well have numerous inclusions of open field lines as evidnced by EIT 285A images (right). This partial view of EIT 285A sun shows that a significant fraction of quiet sun is dark, suggesting that open field lines might originate from it (coronal holes are dark as well, only larger).
Association between X‐ray jets and Hα surges has been addressed in earlier works by Yokoyama & Shibata, 1995; Canfield et al. 1996), who showed both theoretically and observationally that cold chromospheric plasma may accelerate during reconnection between anemerging flux and the coronal field and be observed as Hα surges adjacent to the X‐ray jet. However, a statistical study of X‐ray jets and Hα surges has not yet been conducted. A coordinated observational campaign between Hinode XRT and Hα telescopes (as well as other wavelength such as those used in TRACE experiment) would be beneficial for better understanding of the underlying dynamics of magnetic fields. |
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