Spectroscopic Observations and Modelling of Impulsive Alfv\'en Waves Along a Polar Coronal Jet

Using the Hinode/EIS 2$"$ spectroscopic observations, we study the intensity, velocity, and FWHM variations of the strongest Fe XII 195.12 \AA\ line along the jet to find the signature of Alfv\'en waves. We simulate numerically the impulsively generated Alfv\'en waves within the vertical Harris current-sheet, forming the jet plasma flows, and mimicking their observational signatures. Using the FLASH code and the atmospheric model with embedded weakly expanding magnetic field configuration within a vertical Harris current-sheet, we solve the two and half-dimensional (2.5-D) ideal magnetohydrodynamic (MHD) equations to study the evolution of Alfv\'en waves and vertical flows forming the plasma jet. At a height of $\sim 5~\mathrm{Mm}$ from the base of the jet, the red-shifted velocity component of Fe XII 195.12 \AA\ line attains its maximum ($5~\mathrm{km\,s}^{-1}$) which converts into a blue-shifted one between the altitude of $5-10~\mathrm{Mm}$. The spectral intensity continously increases up to $10~\mathrm{Mm}$, while FWHM still exhibits the low values with almost constant trend. This indicates that the reconnection point within the jet's magnetic field topology lies in the corona $5-10~\mathrm{Mm}$ from its footpoint anchored in the Sun's surface. Beyond this height, FWHM shows a growing trend. This may be the signature of Alfv\'en waves that impulsively evolve due to reconnection and propagate along the jet. From our numerical data, we evaluate space- and time- averaged Alfv\'en waves velocity amplitudes at different heights in the jet's current-sheet, which contribute to the non-thermal motions and spectral line broadening. The synthetic width of Fe XII $195.12~\mathrm{\AA}$ line exhibits similar trend of increment as in the observational data, possibly proving the existence of impulsively generated (by reconnection) Alfv\'en waves which propagate along the jet

Observational Evidence of Sausage-Pinch Instability in Solar Corona by SDO/AIA

We present the first observational evidence of the evolution of sausage-pinch instability in Active Region 11295 during a prominence eruption using data recorded on 12 September 2011 by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We have identified a magnetic flux tube visible in AIA 304 \AA\ that shows curvatures on its surface with variable cross-sections as well as enhanced brightness. These curvatures evolved and thereafter smoothed out within a time-scale of a minute. The curved locations on the flux tube exhibit a radial outward enhancement of the surface of about 1-2 Mm (factor of 2 larger than the original thickness of the flux tube) from the equilibrium position. AIA 193 \AA\ snapshots also show the formation of bright knots and narrow regions inbetween at the four locations as that of 304 \AA\ along the flux tube where plasma emission is larger compared to the background. The formation of bright knots over an entire flux tube as well as the narrow regions in < 60 s may be the morphological signature of the sausage instability. We also find the flows of the confined plasma in these bright knots along the field lines, which indicates the dynamicity of the flux tube that probably causes the dominance of the longitudinal field component over short temporal scales. The observed longitudinal motion of the plasma frozen in the magnetic field lines further vanishes the formed curvatures and plasma confinements as well as growth of instability to stablize the flux tube.Comment: 12 pages, 5 figure

Rotating Network Jets in the quiet Sun as Observed by IRIS

Aims. We perform a detailed observational analysis of network jets to understand their kinematics, rotational motion and underlying triggering mechanism(s). We have analyzed the quiet-Sun (QS) data. Methods. IRIS high resolution imaging and spectral observations (SJI: Si iv 1400.0 \AA, Raster: Si iv 1393.75 \AA) are used to analyze the omnipresent rotating network jets in the transition-region (TR). In addition, we have also used Atmospheric Imaging Assembly (AIA) onboard Solar Dynamic Observation (SDO) observations. Results. The statistical analysis of fifty-one network jets is performed to understand various their mean properties, e.g., apparent speed (140.16+/-39.41 km/s), length (3.16+/-1.18 Mm), lifetimes (105.49+/-51.75 s). The Si iv 1393.75 \AA line has secondary component along with its main Gaussian, which is formed due to the high-speed plasma flows (i.e., network jets). The variation of Doppler velocity across these jets (i.e., blue shift on one edge and red shift on the other) signify the presence of inherited rotational motion. The statistical analysis predicts that the mean rotational velocity (i.e., \delV) is 49.56 km/s. The network jets have high angular velocity in comparison to the other class of solar jets. Conclusions. The signature of network jets are inherited in TR spectral lines in terms of the secondary component of the Si iv 1393.75 \AA line. The rotational motion of network jets is omnipresent, which is reported firstly for this class of jet-like features. The magnetic reconnection seems to be the most favorable mechanism for the formation of these network jets.Comment: 14 Pages; 6 Figures; In Press Astronomy & Astrophysic