No abstract

In this paper, we use the Si iv 1393.755 Å spectral line observed by the Interface Region Imaging Spectrograph (IRIS) in the quiet-Sun (QS) to determine the physical nature of the solar transition region (TR) oscillations. We analyse the properties of these oscillations using wavelet tools (e.g. power, cross-power, coherence, and phase difference) along with the stringent noise model (i.e. power law + constant). We estimate the period of the intensity and Doppler velocity oscillations at each chosen location in the QS and quantify the distribution of the statistically significant power and associated periods in one bright region and two dark regions. In the bright TR region, the mean periods in intensity and velocity are 7 min and 8 min, respectively. In the dark regions, the mean periods in intensity and velocity are 7 min and 5.4 min, respectively. We also estimate the phase difference between the intensity and Doppler velocity oscillations at each location. The statistical distribution of the phase difference is estimated, which peaks at −119° ± 13°, 33° ± 10°, 102° ± 10° in the bright region and at −153° ± 13°, 6° ± 20°, 151° ± 10° in the dark regions. The statistical distribution reveals that the oscillations are caused by propagating slow magneto-acoustic waves encountered with the TR. Some of these locations may also be associated with standing slow waves. Moreover, in the given time domain, several locations exhibit the presence of both propagating and standing oscillations at different frequencies.

We studied a blowout jet that occurred at the west limb of the Sun on 2014 August 29 using high-resolution imaging/spectroscopic observations provided by the Solar Dynamics Observatory/Atmospheric Imaging Assembly and the Interface Region Imaging Spectrograph. An inverse γ-shaped flux rope appeared before the jet–morphological indication of the onset of kink instability. The twisted field lines of the kink-unstable flux rope reconnected at its bright knot and launched the blowout jet at ≈06:30:43 UT with an average speed of 234 km s−1. Just after the launch, the northern leg of the flux rope erupted completely. The time–distance diagrams show multiple spikes or bright dots, which is the result of periodic fluctuations, i.e., quasi-periodic fluctuations (QPPs). The wavelet analysis confirms that QPPs have a dominant period of ≈3 minutes. IRIS spectra (Si iv, C ii, and Mg ii) may also indicate the occurrence of magnetic reconnection through the existence of broad and complex profiles and bidirectional flows in the jet. Further, we found that line broadening is periodic with a period of ≈3 minutes, and plasma upflow always occurs when the line width is high, i.e., multiple reconnection may produce periodic line broadening. The emission measure (EM) curves also show the same period of ≈3 minutes in different temperature bins. The images and EM show that this jet spire is mainly cool (chromospheric/transition region) rather than hot (coronal) material. Further, line broadening, intensity, and EM curves have a period of ≈3 minutes, which strongly supports the fact that multiple magnetic reconnection triggers QPPs in the blowout jet.

Multiwavelength observations of the propagating disturbances (PDs), discovered by Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO), are analyzed to determine their driving mechanism and physical nature. Two magnetic strands in the localized corona are observed to approach and merge with each other, followed by the generation of brightening, which further propagates in a cusp-shaped magnetic channel. Differential emission measure analysis shows an occurrence of heating in this region of interest. We extrapolate potential magnetic field lines at coronal heights from the observed Helioseismic and Magnetic Imager vector magnetogram via Green’s function method using MPI-AMRVAC. We analyze the field to locate magnetic nulls and quasi-separatrix layers (QSLs), which are preferential locations for magnetic reconnection. Dominant QSLs including a magnetic null are found to exist and match the geometry followed by PDs; therefore, this provides conclusive evidence of magnetic reconnection. In addition, spectroscopic analysis of Interface Region Imaging Spectrograph Si iv λ1393.77 line profiles show a rise of line width in the same time range depicting the presence of mass motion in the observed cusp-shaped region. PDs are observed to exhibit periodicities of around 4 minutes. The speeds of PDs measured by the surfing transform technique are close to each other in four different SDO/AIA bandpasses, i.e., 304, 171, 193, and 131 Å, excluding the interpretation of PDs in terms of slow magnetoacoustic waves. We describe comprehensively the observed PDs as quasiperiodic plasma flows generated as a result of periodic reconnection in the vicinity of a coronal magnetic null.