Abstract
Context. Hot coronal jets are a basic observed feature of the solar atmosphere whose physical origin is still actively debated. Aims. We study six recurrent jets that occurred in active region NOAA 12644 on April 4, 2017. They are observed in all the hot filters of AIA as well as cool surges in IRIS slit–jaw high spatial and temporal resolution images. Methods. The AIA filters allow us to study the temperature and the emission measure of the jets using the filter ratio method. We studied the pre-jet phases by analysing the intensity oscillations at the base of the jets with the wavelet technique. Results. A fine co-alignment of the AIA and IRIS data shows that the jets are initiated at the top of a canopy-like double-chambered structure with cool emission on one and hot emission on the other side. The hot jets are collimated in the hot temperature filters, have high velocities (around 250 km s−1) and are accompanied by cool surges and ejected kernels that both move at about 45 km s−1. In the pre-phase of the jets, we find quasi-periodic intensity oscillations at their base that are in phase with small ejections; they have a period of between 2 and 6 min, and are reminiscent of acoustic or magnetohydrodynamic waves. Conclusions. This series of jets and surges provides a good case study for testing the 2D and 3D magnetohydrodynamic emerging flux models. The double-chambered structure that is found in the observations corresponds to the regions with cold and hot loops that are in the models below the current sheet that contains the reconnection site. The cool surge with kernels is comparable with the cool ejection and plasmoids that naturally appears in the models.
Highlights
Solar coronal jets are detected throughout the entire solar cycle in a wide wavelength range, from X-rays (Shibata et al 1992) to the extreme ultraviolet (EUV; Wang et al 1998; Alexander & Fletcher 1999; Innes et al 2011; Sterling et al 2015; Chandra et al 2015; Joshi et al 2017a)
Other interesting ejections are cool surges, which emerge in the form of unwrinkled threads of dark material in Hα (Roy 1973; Mandrini et al 2002; Uddin et al 2012; Li et al 2016), and sprays, which are very fast ejections that generally originate in active region filaments (Warwick 1957; Tandberg-Hanssen et al 1980; Pike & Mason 2002; Martin 2015)
In our observations in the beginning phase of the jets, the area of the northern and southern vaults is 1.4×1018 and 1.16×1018 cm2, respectively, and during the jet phase (11:47 UT), they become 1.05×1018 and 2.2×1018 cm2, respectively. This suggests that while the reconnection occurs, the emerging volume decreases, whereas the reconnected loop domain grows, as in the emerging flux models (Moreno-Insertis et al 2008; Moreno-Insertis & Galsgaard 2013; Nóbrega-Siverio et al 2016). (b) One main item for identifying the observation with the flux emergence models is the possibility that we observe a wide, cool, and dense plasma surge that is ejected in the neighbourhood of the vault and jet complex
Summary
Solar coronal jets are detected throughout the entire solar cycle in a wide wavelength range, from X-rays (Shibata et al 1992) to the extreme ultraviolet (EUV; Wang et al 1998; Alexander & Fletcher 1999; Innes et al 2011; Sterling et al 2015; Chandra et al 2015; Joshi et al 2017a). Pucci et al (2012) analysed the X-ray jets observed by Hinode November 2−4, 2007 and found that most of the jets are associated with oscillations of the coronal emission in bright points (for a recent review of coronal bright points, see Madjarska 2019) at the base of the jets They concluded that the pre-jet oscillations are the result of the change in area or temperature of the pre-jet activity region. We are able to identify a candidate location for the current sheet and reconnection site, and we follow the evolution of the cool surge and hot jets with individual blob ejections This is a clear case study for 2D and 3D MHD models where flux emergence is the trigger of the jet.
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