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Multi-thermal atmosphere of a mini-solar flare during magnetic reconnection observed with IRIS  

Reetika Joshi   Submitted: 2021-02-05 13:12

Context. The Interface Region Imaging Spectrograph (IRIS) with its high spatial and temporal resolution facilitates exceptional plasma diagnostics of solar chromospheric and coronal activity during magnetic reconnection. Aims. The aim of this work is to study the fine structure and dynamics of the plasma at a jet base forming a mini-flare between two emerging magnetic fluxes (EMFs) observed with IRIS and the Solar Dynamics Observatory instruments. Methods. We proceed to a spatio-temporal analysis of IRIS spectra observed in the spectral ranges of Mg II, C II, and Si IV ions. Doppler velocities from Mg II lines were computed using a cloud model technique. Results. Strong asymmetric Mg II and C II line profiles with extended blue wings observed at the reconnection site (jet base) are interpreted by the presence of two chromospheric temperature clouds: one explosive cloud with blueshifts at 290 km s-1 and one cloud with smaller Doppler shift (around 36 km s-1 ). Simultaneously at the same location (jet base), strong emission of several transition region lines (e.g. O IV and Si IV), emission of the Mg II triplet lines, and absorption of identified chromospheric lines in Si IV broad profiles have been observed and analysed. Conclusions. Such observations of IRIS line and continuum emissions allow us to propose a stratification model for the white light, mini-flare atmosphere with multiple layers of different temperatures along the line of sight in a reconnection current sheet. It is the first time that we could quantify the fast speed (possibly Alfvénic flows) of cool clouds ejected perpendicularly to the jet direction via the cloud model technique. We conjecture that the ejected clouds come from plasma which was trapped between the two EMFs before reconnection or be caused by chromospheric-temperature (cool) upflow material similar to a surge during reconnection

Authors: Reetika Joshi,Brigitte Schmieder, Akiko Tei, Guillaume Aulanier, Juraj Lörincík, Ramesh Chandra, and Petr Heinzel
Projects: None

Publication Status: Published
Last Modified: 2021-02-06 13:54
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Cause and Kinematics of a Jetlike CME  

Reetika Joshi   Submitted: 2020-10-30 06:58

In this article, we present the multi-viewpoint and multiwavelength analysis of an atypical solar jet based on data from Solar Dynamics Observatory, SOlar, and Heliospheric Observatory, and Solar TErrestrial RElations Observatory. It is generally believed that coronal mass ejections (CMEs) develop from the large-scale solar eruptions in the lower atmosphere. However, the kinematical and spatial evolution of the jet on 2013 April 28 suggests that the jet was clearly associated with a narrow CME with a width of ≍25° and a speed of ≍450 km s-1. To better understand the link between the jet and the CME, we performed a coronal potential field extrapolation from the line-of-sight magnetogram of the active region. The extrapolations suggest that the jet eruption follows the same path of the open magnetic field lines from the source region, which provides a route for the jet material to escape from the solar surface toward the outer corona.

Authors: Reetika Joshi, Yuming Wang, Ramesh Chandra, Quanhao Zhang, Lijuan Liu , and Xiaolei Li
Projects: None

Publication Status: Accepted
Last Modified: 2020-11-01 22:32
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The role of small-scale surface motions in the transfer of twist to a solar jet from a remote stable flux rope  

Reetika Joshi   Submitted: 2020-10-30 06:56

Context. Jets often have a helical structure containing ejected plasma that is both hot and also cooler and denser than the corona. Various mechanisms have been proposed to explain how jets are triggered, primarily attributed to a magnetic reconnection between the emergence of magnetic flux and environment or that of twisted photospheric motions that bring the system into a state of instability. Aims. Multi-wavelength observations of a twisted jet observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory and the Interface Region Imaging Spectrograph (IRIS) were used to understand how the twist was injected into the jet, thanks to the IRIS spectrographic slit fortuitously crossing the reconnection site at that time. Methods. We followed the magnetic history of the active region based on the analysis of the Helioseismic and Magnetic Imager vector magnetic field computed with the UNNOFIT code. The nature and dynamics of the jet reconnection site are characterized by the IRIS spectra. Results. This region is the result of the collapse of two emerging magnetic fluxes (EMFs) overlaid by arch filament systems that have been well-observed with AIA, IRIS, and the New Vacuum Solar Telescope in Hα. In the magnetic field maps, we found evidence of the pattern of a long sigmoidal flux rope (FR) along the polarity inversion line between the two EMFs, which is the site of the reconnection. Before the jet, an extension of the FR was present and a part of it was detached and formed a small bipole with a bald patch (BP) region, which dynamically became an X-current sheet over the dome of one EMF where the reconnection took place. At the time of the reconnection, the Mg II spectra exhibited a strong extension of the blue wing that is decreasing over a distance of 10 Mm (from -300 km s-1 to a few km s-1). This is the signature of the transfer of the twist to the jet. Conclusions. A comparison with numerical magnetohydrodynamics simulations confirms the existence of the long FR. We conjecture that there is a transfer of twist to the jet during the extension of the FR to the reconnection site without FR eruption. The reconnection would start in the low atmosphere in the BP reconnection region and extend at an X-point along the current sheet formed above.

Authors: Reetika Joshi, Brigitte Schmieder, Guillaume Aulanier, véronique Bommier, Ramesh Chandra
Projects: None

Publication Status: Accepted
Last Modified: 2020-11-01 22:32
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Case study of multi-temperature coronal jets for emerging flux MHD models  

Reetika Joshi   Submitted: 2020-07-16 11:24

Hot coronal jets are a basic observed feature of the solar atmosphere whose physical origin is still actively debated. 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. 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 analyzing the intensity oscillations at the base of the jets with the wavelet technique. 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 (250 km s-1) and are accompanied by cool surges and kernels that both move at 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. 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 appear in the models.

Authors: Reetika Joshi, Ramesh Chandra, Brigitte Schmieder, Fernando Moreno-Insertis, Guillaume Aulanier, Daniel Nóbrega-Siverio, and Pooja Devi
Projects: None

Publication Status: Accepted
Last Modified: 2020-07-18 21:49
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Slippage of Jets Explained by the Magnetic Topology of NOAA Active Region 12035  

Reetika Joshi   Submitted: 2017-09-10 21:01

In this study, we present the investigation of eleven recurring solar jets originated from two different sites (site 1 and site 2) close to each other (~ 11 Mm) in the NOAA active region (AR) 12035 during 15-16 April 2014. The jets were observed by the Atmospheric Imaging Assembly (AIA) telescope onboard the Solar Dynamics Observatory (SDO) satellite. Two jets were observed by the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, India telescope in Hα . On 15 April flux emergence is important in site 1 while on 16 April flux emergence and cancellation mechanisms are involved in both sites. The jets of both sites have parallel trajectories and move to the south with a speed between 100 and 360 km s-1. We observed some connection between the two sites with some transfer of brightening. The jets of site 2 occurred during the second day and have a tendency to move towards the jets of site 1 and merge with them. We conjecture that the slippage of the jets could be explained by the complex topology of the region with the presence of a few low-altitude null points and many quasi-separatrix layers (QSLs), which could intersect with one another.

Authors: R. Joshi, B. Schmieder, R. Chandra, G. Aulanier, F.P. Zuccarello, W. Uddin
Projects: None

Publication Status: Accepted for publication in Solar Physics
Last Modified: 2017-09-13 12:22
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Abstracts by Author
Multi-thermal atmosphere of a mini-solar flare during magnetic reconnection observed with IRIS
Cause and Kinematics of a Jetlike CME
The role of small-scale surface motions in the transfer of twist to a solar jet from a remote stable flux rope
Case study of multi-temperature coronal jets for emerging flux MHD models
Slippage of Jets Explained by the Magnetic Topology of NOAA Active Region 12035

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