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We present the formation of quasi-periodic cool spicule-like jets in the solar atmosphere using 2.5-D numerical simulation in two-fluid regime (ions+neutrals) under the presence of thermal conduction and ion-neutral collision. The non-linear, impulsive Alfv\'enic perturbations at the top of the photosphere trigger field aligned magnetoacoustic perturbations due to ponderomotive force. The transport of energy from Alfv\'en pulse to such vertical velocity perturbations due to ponderomotive force is considered as an initial trigger mechanism. Thereafter, these velocity perturbations steepen into the shocks followed by quasi-periodic rise and fall of the cool jets transporting mass in the overlying corona., Comment: In Press; Philosophical Transactions of the Royal Society A; 21 Pages; 06 Figures. Philosophical Transactions is the oldest English science journal in the world, which has been published continuously since March 1665 as launched by Henry Oldenburg

Coronal Mass Ejections (CMEs) are the most energetic expulsions of magnetized plasma from the Sun that play a crucial role in space weather dynamics. This study investigates the diverse kinematics and thermodynamic evolution of two CMEs (CME1: 2011 September 24 and CME2: 2018 August 20) at coronal heights where thermodynamic measurements are limited. The peak 3D propagation speed of CME1 is high (1,885 km/s) with two-phase expansion (rapid and nearly constant), while the peak 3D propagation speed of CME2 is slow (420 km/s) with only a gradual expansion. We estimate the distance-dependent variations in the polytropic index, heating rate, temperature, and internal forces implementing the revised FRIS model, taking inputs of 3D kinematics estimated from the GCS model. We find CME1 exhibiting heat-release during its early-rapid acceleration decrease and jumps to the heat-absorption state during its constant acceleration phase. In contrast to CME1, CME2 shows a gradual transition from the near-adiabatic to the heat-absorption state during its gradually increasing acceleration. Our analysis reveals that although both CMEs show differential heating, they experience heat-absorption during their later propagation phases, approaching the isothermal state. The faster CME1 achieves an adiabatic state followed by an isothermal state at smaller distances from the Sun than the slower CME2. We also find that the expansion of CMEs is primarily influenced by centrifugal and thermal pressure forces, with the Lorentz force impeding expansion. Multi-wavelength observations of flux-ropes at source regions support the FRIS model-derived findings at initially observed lower coronal heights., Comment: 23 pages, 9 figures, accepted for publication in The Astrophysical Journal (ApJ)

Multiwavelength observations of the propagating disturbances (PDs), discovered by Atmospheric Imaging Assembly (AIA) onboard Solar Dynamics Observatory (SDO), are analyzed to determine its driving mechanism and physical nature. Two magnetic strands in the localised 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 (ROI). We extrapolate potential magnetic field lines at coronal heights from observed Helioseismic and Magnetic Imager (HMI) 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, it provides conclusive evidence of magnetic reconnection. In addition, spectroscopic analysis of Interface Region Imaging Spectrograph (IRIS) Si IV 1393.77 {\AA} line profiles show a rise of line-width in the same time range depicting presence of mass motion in the observed cusp-shaped region. PDs are observed to exhibit periodicities of around four minutes. The speeds of PDs measured by Surfing Transform Technique are almost close to each other in four different SDO/AIA bandpasses, i.e., 304, 171, 193 and 131 {\AA} excluding the interpretation of PDs in terms of slow magnetoacoustic waves. We describe comprehensively the observed PDs as quasi-periodic plasma flows generated due to periodic reconnection in vicinity of a coronal magnetic null., Comment: 21 Pages; 10 Figures; Accepted for the Publication in The Astrophysical Journal

We study a blowout jet that occurs at the west limb of the Sun on August 29$^{th}$, 2014 using high-resolution imaging/spectroscopic observations provided by SDO/AIA and IRIS. An inverse $\gamma$-shape flux-rope appears before the jet{--} morphological indication of the onset of kink instability. The twisted field lines of kink-unstable flux-rope reconnect at its bright knot and launch the blowout jet at $\approx$06:30:43 UT with an average speed of 234 km s$^{-1}$. Just after the launch, the northern leg of the flux rope erupts 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 $\approx$ 03 minutes. IRIS spectra (Si~{\sc iv}, C~{\sc ii}, and Mg~{\sc ii}) may also indicate the occurrence of magnetic reconnection through existence of broad $\&$ complex profiles and bi-directional flows in the jet. Further, we have found that line broadening is periodic with a period of $\approx$ 03 minutes, and plasma upflow is always occurs when the line width is high, i.e., multiple reconnection may produce periodic line broadening. The EM curves also show the same period of $\approx$ 03 minutes in different temperature bins. The images and EM show that this jets spire is mainly cool (chromospheric/transition region) rather than hot (coronal) material. Further, line broadening, intensity, and EM curves have a period of $\approx$03 minutes, which strongly supports that multiple magnetic reconnection triggers QPPs in the blowout jet., Comment: The Astrophysical Journal (In press), 25 pages, 12 figures

We use multiwavelength imaging observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) to study the evolution of Kelvin-Helmholtz (K-H) instability in a fan-spine magnetic field configuration. This magnetic topology exists near an active region AR12297 and is rooted in a nearby sunspot. In this magnetic configuration, two layers of cool plasma flow in parallel and interact with each other inside an elongated spine. The slower plasma flow (5 $km s^{-1}$) is the reflected stream along the spine field lines from the top, which interacts with the impulsive plasma upflows (114-144 km s$^{-1}$) from below. This process generates a shear motion and subsequent evolution of the K--H instability. The amplitude and characteristic wavelength of the K-H unstable vortices increase, satisfying the criterion of the fastest growing mode of this instability. We also describe that the velocity difference between two layers and velocity of K-H unstable vortices are greater than the Alfven speed in the second denser layer, which also satisfies the criterion of the growth of K-H instability. In the presence of the magnetic field and sheared counter streaming plasma as observed in the fan-spine topology, we estimate the parametric constant, $\Lambda\ge$1, that confirms the dominance of velocity shear and the evolution of the linear phase of the K-H instability. This observation indicates that in the presence of complex magnetic field structuring and flows, the fan-spine configuration may evolve into rapid heating, while the connectivity changes due to the fragmentation via the K-H instability., Comment: 14 pages, 8 figures, accepted for publication in ApJ

Using the multi-temperature observations from SDO/AIA on 30th December 2019, we provide a signature of prominence driven forced magnetic reconnection in the corona and associated plasma dynamics during 09:20 UT to 10:38 UT. A hot prominence segment erupts with a speed of 21 km/s and destabilises the entire prominence system. Thereafter, it rose upward in the north during 09:28 UT to 09:48 UT with a speed of 24 km/s. The eruptive prominence stretches overlying field lines upward with the speed of 27-28 km/s , which further undergo into the forced reconnection. The coronal plasma also flows in southward direction with the speed of 7 km/s, and both these inflows trigger the reconnection at 09:48 UT. Thereafter, the east and westward magnetic channels are developed and separated. The east-west reorganization of the magnetic fields starts creating bi-directional plasma outflows towards the limb with their respective speed of 28 km/s and 37 km/s. Their upper ends are diffused in the overlying corona, transporting another set of upflows with the speed of 22 km/s and 19 km/s. The multi-temperature plasma (Te=6.0-7.2) evolves and elongated upto a length of ~10^5 km on the reorganized fields. The hot plasma and remaining prominence threads move from reconnection region towards another segment of prominence in the eastward direction. The prominence-prominence/loop interaction and associated reconnection generate jet-like eruptions with the speed of 178-183 km/s. After the formation of jet, the overlying magnetic channel is disappeared in the corona., Comment: The Astrophysical Journal; 12 Pages; 06 Figures

We analyze the characteristics of a quiescent polar prominence using the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). Initially, small-scale barb-like structures are evident on the solar disk, which firstly grow vertically and thereafter move towards the south-west limb. Later, a spine connects these barbs and we observe apparent rotating motions in the upper part of the prominence. These apparent rotating motions might play an important role for the evolution and growth of the filament by transferring cool plasma and magnetic twist. The large-scale vortex motion is evident in the upper part of the prominence, and consists of a swirl-like structure within it. The slow motion of the footpoint twists the legs of the prominence due to magnetic shear, causing two different kinds of magnetic reconnection. The internal reconnection is initiated by a resistive tearing-mode instability, which leads to the formation of multiple plasmoids in the elongated current sheet. The estimated growth rate was found to be 0.02--0.05. The magnetic reconnection heats the current sheet for a small duration. However, most of the energy release due to magnetic reconnection is absorbed by the surrounding cool and dense plasma and used to accelerate the plasmoid ejection. The multiple plasmoid ejections destroy the current sheet. Therefore, the magnetic arcades collapse near the X-point. Oppositely directed magnetic arcades may reconnect with the southern segment of the prominence and an elongated thin current sheet is formed. This external reconnection drives prominence eruption., Comment: 21 pages, 11 figures, Accepted for publication in Solar Physicss

We analyze the eruption of a coronal plasma channel (CPC) and an overlying flux rope using \textit{Atmospheric Imaging Assembly/Solar Dynamic Observatory} (AIA/SDO) and \textit{Solar TErrestrial RElations Observatory} (STEREO)-A spacecraft data. The CPC erupted first with its low and very faint coronal signature. Later, above the CPC, a diffuse and thin flux rope also developed and erupted. The spreading CPC further triggered a rotating jet-like structure from the coronal hole lying to its northward end. This jet-like eruption may have evolved due to the interaction between spreading CPC and the open field lines of the coronal hole lying towards its northward foot-point. The CPC connected two small trans-equatorial coronal holes lying respectively in the northern and southern hemisphere on either side of the Equator. These eruptions were collectively associated with the stealth-type CMEs and CME associated with a jet-like eruption. The source region of the stealth CMEs lay between two coronal holes connected by a coronal plasma channel. Another CME was also associated with a jet-like eruption that occurred from the coronal hole in the northern hemisphere. These CMEs evolved without any low coronal signature and yet were responsible for the third strongest geomagnetic storm of Solar cycle 24. These stealth CMEs further merged and collectively passed through the interplanetary space. The compound CME further produced an intense geomagnetic storm (GMS) with Dst index= -176 nT. The $z$-component of the interplanetary magnetic field [$B_{z}$] switched to negative (-18 nT) during this interaction, and simultaneous measurement of the disturbance in the Earth's magnetic field (Kp=7) indicates the onset of the geomagnetic storm.

MRT unstable plumes are observed in a loop-like eruptive prominence using SDO/AIA observations. The small-scale cavities are developed within the prominence, where perturbations trigger dark plumes (P1 \& P2) propagating with the speed of 35-46 km s$^{-1} $. The self-similar plume formation shows initially the growth of linear MRT unstable plume (P1), and thereafter the evolution of non-linear single mode MRT unstable second plume (P2). The Differential Emission Measure (DEM) analysis shows that plumes are less denser and hotter than the prominence. We have estimated the observational growth rate for both plumes as 1.32$\pm$0.29$\times$ 10$^{-3}$ s$^{-1}$ and 1.48$\pm$0.29$\times$ 10$^{-3}$ s$^{-1}$ respectively, which are comparable to the estimated theoretical growth rate (1.95$\times$ 10$^{-3}$ s$^{-1}$) . The nonlinear phase of an MRT unstable plume (P2) may collapse via Kelvin-Helmholtz vortex formation in the downfalling plasma. Later, a plasma thread has been evident in the rising segment of this prominence. It may be associated with the tangled field and Rayleigh-Taylor instability. The tangled field initiates shearing at the prominence-cavity boundary. Due to this shear motion, the plasma downfall has occurred at the right part of the prominence-cavity boundary. It triggers the characteristic of KH unstable vortices and MRT unstable plasma bubbles propagating at different speeds and merging with each other. The shear motion and lateral plasma downfall may initiate hybrid KH-RT instability there., Comment: 25 pages, 8 figures, 1 table

Using multiwavelength imaging observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) on 03 May 2012, we present a novel physical scenario for the formation of a temporary X-point in the solar corona, where plasma dynamics is forced externally by a moving prominence. Natural diffusion was not predominant, however, a prominence driven inflow occurred firstly, forming a thin current sheet and thereafter enabling a forced magnetic reconnection at a considerably high rate. Observations in relation to the numerical model reveal that forced reconnection may rapidly and efficiently occur at higher rates in the solar corona. This physical process may also heat the corona locally even without establishing a significant and self-consistent diffusion region. Using a parametric numerical study, we demonstrate that the implementation of the external driver increases the rate of the reconnection even when the resistivity required for creating normal diffusion region decreases at the X-point. We conjecture that the appropriate external forcing can bring the oppositely directed field lines into the temporarily created diffusion region firstly via the plasma inflows as seen in the observations. The reconnection and related plasma outflows may occur thereafter at considerably larger rates., Comment: 14 Pages; 07 Figures; The Astrophysical Journal (in press)

We analyze the observations from Solar TErrestrial RElations Observatory (STEREO)-A\&B/COR-1 of an eruptive prominence in the intermediate corona on 7 June 2011 at 08:45 UT, which consists of magnetic Rayleigh-Taylor (MRT) unstable plasma segments. Its upper northward segment shows spatio-temporal evolution of MRT instability in form of finger structures upto the outer corona and low inter-planetary space. Using method of Dolei et al.(2014), It is estimated that the density in each bright finger is greater than corresponding dark region lying below of it in the surrounding intermediate corona. The instability is evolved due to wave perturbations that are parallel to the magnetic field at the density interface. We conjecture that the prominence plasma is supported by tension component of the magnetic field against gravity. Using linear stability theory, magnetic field is estimated as 21-40 mG to suppress growth of MRT in the observed finger structures. In the southward plasma segment, a horn-like structure is observed at 11:55 UT in the intermediate corona that also indicates MRT instability. Falling blobs are also observed in both the plasma segments. In the outer corona upto 6-13 solar radii, the mushroom-like plasma structures have been identified in the upper northward MRT unstable plasma segment using STEREO-A/COR-2. These structures most likely grew due to the breaking and twisting of fingers at large spatial scales in weaker magnetic fields. In the lower inter-planetary space upto 20 solar radii, these structures are fragmented into various small-scale localized plasma spikes most likely due to turbulent mixing., Comment: 19 Pages, 6 Figures, 1 Table (In Press ApJ)