arXiv subjects

J. Martinez-Sykora

Publications and source records attributed to J. Martinez-Sykora.

15 recordsLinked to original sources

arXiv2025

Coronal energy release by MHD avalanches III. Identification of a reconnection outflow from a nanoflare

Outflows perpendicular to the guide field are believed to be a possible signature of magnetic reconnection in the solar corona and specifically a way to detect the occurrence of ubiquitous small-angle magnetic reconnection. The aim of this work is to identify possible diagnostic techniques of such outflows in hot coronal loops with SDO/AIA and the forthcoming MUltislit Solar Explorer (MUSE), in a realistically dynamic coronal loop environment in which an MHD avalanche is occurring. We consider a 3D MHD model of two magnetic flux tubes, including a stratified, radiative and thermal-conducting atmosphere, twisted by footpoint rotation. The faster rotating flux tube becomes kink-unstable and soon involves the other one in the avalanche. The turbulent decay of this magnetic structure on a global scale leads to the formation, fragmentation, and dissipation of current sheets driving impulsive heating akin to a nanoflare storm. We captured a clear outflow from a reconnection episode soon after the initial avalanche and synthesized its emission as detectable with AIA and MUSE. The outflow has a maximum temperature around 8 MK, a total energy of 1024 erg, a velocity of a few hundred km/s, and a duration of less than 1 min. We show the emission in the AIA 94 A channel (Fe XVIII line) and in the MUSE 108 A Fe XIX spectral line. his outflow shares many features with nanojets recently detected at lower temperatures. Its low emission measure makes, however, its detection difficult with AIA, but Doppler shifts can be measured with MUSE. Conditions become different in a later steady state phase when the flux tubes are filled with denser and relatively cooler plasma.

astro-ph.SR↗

arXiv2024

Coronal energy release by MHD avalanches II. EUV line emission from a multi-threaded coronal loop

MHD kink instability can trigger the fragmentation of a twisted magnetic flux tube into small-scale current sheets that dissipate as aperiodic impulsive heating events. This instability propagates as an avalanche to nearby flux tubes and leads to a nanoflare storm. Our previous work was devoted to related 3D MHD numerical modeling with a stratified and realistic atmosphere. This work addresses predictions for the EUV imaging spectroscopy of such structure and evolution of a loop, with an average temperature of 2.5 MK in the solar corona. We set a particular focus on the forthcoming MUSE mission. From the output of the numerical simulations, we synthesized the intensities, Doppler shifts, and non-thermal line broadening in 3 EUV spectral lines in the MUSE passbands: Fe IX 171A, Fe XV 284 A, and Fe XIX 108 A, at 1 MK, 2 MK, and 10 MK, respectively, according to the MUSE expected pixel size, temporal resolution, and temperature response functions. We provide maps showing different view angles and realistic spectra. Finally, we discuss the relevant evolutionary processes from the perspective of possible observations. We find that the MUSE observations might be able to detect the fine structure determined by tube fragmentation. In particular, the Fe IX line is mostly emitted at the loop footpoints, where we track the motions that drive the magnetic stressing and detect the upward motion of evaporating plasma from the chromosphere. In Fe XV, we see the bulk of the loop with increasing intensity. The Fe XIX line is very faint within the chosen simulation parameters; thus, any transient brightening around the loop apex may possibly be emphasized by the folding of sheet-like structure. In conclusion, we show that coronal loop observations with MUSE can pinpoint some crucial features of MHD-modeled ignition processes, such as the related dynamics, helping to identify the heating processes.

astro-ph.SR↗

arXiv2023

Unified fluid-model theory of $\mathbf{E}\times\mathbf{B}$ instabilities in low-ionized collisional plasmas with arbitrarily magnetized multi-species ions

This paper develops a unified linear theory of local cross-field plasma instabilities, such as the Farley-Buneman, electron thermal, and ion thermal instabilities, in collisional plasmas with fully or partially unmagnetized multi-species ions. Collisional lasma instabilities in low-ionized, highly dissipative, weakly magnetized plasmas play an important role in the lower Earth's ionosphere and may be of importance in other planet ionospheres, star atmospheres, cometary tails, molecular clouds, accretion disks, etc. In the solar chromosphere, macroscopic effects of collisional plasma instabilities may contribute into significant heating -- an effect originally suggested from spectroscopic observations and relevant modeling. Based on a simplified 5-moment multi-fluid model, the theoretical analysis produces the general linear dispersion relation for the combined Thermal-Farley-Buneman Instability (TFBI). Important limiting cases are analyzed in detail. The analysis demonstrates acceptable applicability of this model for the rocesses under study. Fluid-model simulations usually require much less computer resources than do more accurate kinetic simulations, so that the apparent success of this approach to the linear theory of collisional plasma instabilities makes it possible to investigate the TFBI (along with its possible macroscopic effects) using global fluid codes originally developed for large-scale modeling of the solar and planetary atmospheres.

physics.plasm-ph↗

arXiv2022

Multi-Fluid Simulations of Upper Chromospheric Magnetic Reconnection with Helium-Hydrogen mixture

Our understanding of magnetic reconnection (MR) under chromospheric conditions remains limited. Recent observations have demonstrated the important role of ion-neutral interactions in the dynamics of the chromosphere. Furthermore, the comparison between spectral profiles and synthetic observations of reconnection events suggest that current MHD approaches appear to be inconsistent with observations. First, collisions and multi-thermal aspects of the plasma play a role in these regions. Second, hydrogen and helium ionization effects are relevant to the energy balance of the chromosphere. This work investigates multi-fluid multi-species (MFMS) effects on MR in conditions representative of the upper chromosphere using the multi-fluid Ebysus code. We compare an MFMS approach based on a helium-hydrogen mixture with a two-fluid MHD model based on hydrogen only. The simulations of MRs are performed in a Lundquist number regime high enough to develop plasmoids and instabilities. We study the evolution of the MR and compare the two approaches including the structure of the current sheet and plasmoids, the decoupling of the particles, the evolution of the heating mechanisms, and the composition. The presence of helium species leads to more efficient heating mechanisms than the two-fluid case. This scenario, which is out of reach of the two-fluid or single-fluid models, can reach transition region temperatures starting from upper chromospheric thermodynamic conditions, representative of a quiet Sun scenario. The different dynamics between helium and hydrogen species could lead to chemical fractionation and, under certain conditions, enrichment of helium in the strongest outflows. This could be of significance for recent observations of helium enrichment in the solar wind in switchbacks and CMEs.

astro-ph.SR↗

arXiv2021

A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)

The Interface Region Imaging Spectrograph (IRIS) has been obtaining near- and far-ultraviolet images and spectra of the solar atmosphere since July 2013. The unique combination of near and far-ultraviolet spectra and images at subarcsecond resolution and high cadence allows the tracing of mass and energy through the critical interface between the solar surface and the corona or solar wind. IRIS has enabled research into the fundamental physical processes thought to play a role in the low solar atmosphere such as ion-neutral interactions, magnetic reconnection, the generation, propagation, and dissipation of various types of waves, the acceleration of non-thermal particles, and various small-scale instabilities. These new findings have helped provide novel insights into a wide range of phenomena including the discovery of non-thermal particles in coronal nanoflares, the formation and impact of spicules and other jets, resonant absorption and dissipation of Alfvenic waves, energy release associated with braiding of magnetic field lines, the thermal instability in the chromosphere-corona mass and energy cycle, the contribution of waves, turbulence, and non-thermal particles in the energy deposition during flares and smaller-scale events such as UV bursts, and the role of flux ropes and other mechanisms in triggering CMEs. IRIS observations have also advanced studies of the connections between solar and stellar physics. Advances in numerical modeling, inversion codes, and machine learning techniques have played a key role in driving these new insights. With the advent of exciting new instrumentation both on the ground (e.g., DKIST, ALMA) and space-based (e.g., Parker Solar Probe, Solar Orbiter), we aim to review new insights based on IRIS observations or related modeling, and highlight some of the outstanding challenges that have been brought to the fore.

astro-ph.SR↗

arXiv2020

High-resolution observations of the solar photosphere, chromosphere and transition region. A database of coordinated IRIS and SST observations

NASA's Interface Region Imaging Spectrograph (IRIS) provides high resolution observations of the solar atmosphere through UV spectroscopy and imaging. Since the launch of IRIS in June 2013, we have conducted systematic observation campaigns in coordination with the Swedish 1-m Solar Telescope (SST) on La Palma. The SST provides complementary high-resolution observations of the photosphere and chromosphere. The SST observations include spectro-polarimetric imaging in photospheric Fe I lines and spectrally-resolved imaging in the chromospheric Ca II 8542 A, H-alpha, and Ca II K lines. We present a database of co-aligned IRIS and SST datasets that is open for analysis to the scientific community. The database covers a variety of targets including active regions, sunspots, plage, quiet Sun, and coronal holes.

astro-ph.SR↗

arXiv2018

Small-scale magnetic flux emergence in the quiet Sun

Small bipolar magnetic features are observed to appear in the interior of individual granules in the quiet Sun, signaling the emergence of tiny magnetic loops from the solar interior. We study the origin of those features as part of the magnetoconvection process in the top layers of the convection zone. Two quiet-Sun magnetoconvection models, calculated with the radiation-magnetohydrodynamic (MHD) Bifrost code and with domain stretching from the top layers of the convection zone to the corona, are analyzed. Using 3D visualization as well as a posteriori spectral synthesis of Stokes parameters, we detect the repeated emergence of small magnetic elements in the interior of granules, as in the observations. Additionally, we identify the formation of organized horizontal magnetic sheets covering whole granules. Our approach is twofold, calculating statistical properties of the system, like joint probability density functions (JPDFs), and pursuing individual events via visualization tools. We conclude that the small magnetic loops surfacing within individual granules in the observations may originate from sites at or near the downflows in the granular and mesogranular levels, probably in the first 1 or 1.5 Mm below the surface. We also document the creation of granule-covering magnetic sheet-like structures through the sideways expansion of a small subphotospheric magnetic concentration picked up, and pulled out of the interior, by a nascent granule. The sheet-like structures we found in the models may match the recent observations of Centeno et al. (2017).

astro-ph.SR↗

arXiv2017

Intermittent reconnection and plasmoids in UV bursts in the low solar atmosphere

Magnetic reconnection is thought to drive a wide variety of dynamic phenomena in the solar atmosphere. Yet the detailed physical mechanisms driving reconnection are difficult to discern in the remote sensing observations that are used to study the solar atmosphere. In this paper we exploit the high-resolution instruments Interface Region Imaging Spectrograph (IRIS) and the new CHROMIS Fabry-Perot instrument at the Swedish 1-m Solar Telescope (SST) to identify the intermittency of magnetic reconnection and its association with the formation of plasmoids in so-called UV bursts in the low solar atmosphere. The Si IV 1403A UV burst spectra from the transition region show evidence of highly broadened line profiles with often non-Gaussian and triangular shapes, in addition to signatures of bidirectional flows. Such profiles had previously been linked, in idealized numerical simulations, to magnetic reconnection driven by the plasmoid instability. Simultaneous CHROMIS images in the chromospheric Ca II K 3934A line now provide compelling evidence for the presence of plasmoids, by revealing highly dynamic and rapidly moving brightenings that are smaller than 0.2 arcsec and that evolve on timescales of order seconds. Our interpretation of the observations is supported by detailed comparisons with synthetic observables from advanced numerical simulations of magnetic reconnection and associated plasmoids in the chromosphere. Our results highlight how subarcsecond imaging spectroscopy sensitive to a wide range of temperatures combined with advanced numerical simulations that are realistic enough to compare with observations can directly reveal the small-scale physical processes that drive the wide range of phenomena in the solar atmosphere.

astro-ph.SR↗

arXiv2015

Homologous Helical Jets: Observations by IRIS, SDO and Hinode and Magnetic Modeling with Data-Driven Simulations

We report on observations of recurrent jets by instruments onboard the Interface Region Imaging Spectrograph (IRIS), Solar Dynamics Observatory (SDO) and Hinode spacecrafts. Over a 4-hour period on July 21st 2013, recurrent coronal jets were observed to emanate from NOAA Active Region 11793. FUV spectra probing plasma at transition region temperatures show evidence of oppositely directed flows with components reaching Doppler velocities of +/- 100 km/s. Raster Doppler maps using a Si IV transition region line show all four jets to have helical motion of the same sense. Simultaneous observations of the region by SDO and Hinode show that the jets emanate from a source region comprising a pore embedded in the interior of a supergranule. The parasitic pore has opposite polarity flux compared to the surrounding network field. This leads to a spine-fan magnetic topology in the coronal field that is amenable to jet formation. Time-dependent data-driven simulations are used to investigate the underlying drivers for the jets. These numerical experiments show that the emergence of current-carrying magnetic field in the vicinity of the pore supplies the magnetic twist needed for recurrent helical jet formation.

astro-ph.SR↗

arXiv2014

The Unresolved Fine Structure Resolved - IRIS observations of the Solar Transition Region

The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a long standing problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, low lying loops or loop segments at transition-region temperatures that vary rapidly, on the timescales of minutes. We argue that the existence of these loops solves a long standing observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle.

astro-ph.SR↗

arXiv2014

On the prevalence of small-scale twist in the solar chromosphere and transition region

The solar chromosphere and transition region (TR) form an interface between the Sun's surface and its hot outer atmosphere. Here most of the non-thermal energy that powers the solar atmosphere is transformed into heat, although the detailed mechanism remains elusive. High-resolution (0.33-arcsec) observations with NASA's Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere and TR that are replete with twist or torsional motions on sub-arcsecond scales, occurring in active regions, quiet Sun regions, and coronal holes alike. We coordinated observations with the Swedish 1-m Solar Telescope (SST) to quantify these twisting motions and their association with rapid heating to at least TR temperatures. This view of the interface region provides insight into what heats the low solar atmosphere.

astro-ph.SR↗

arXiv2014

The Interface Region Imaging Spectrograph (IRIS)

The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s temporal resolution and 1 km/s velocity resolution over a field-of-view of up to 175 arcsec x 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332-1358, 1389-1407 and 2783-2834 Angstrom including bright spectral lines formed in the chromosphere (Mg II h 2803 Angstrom and Mg II k 2796 Angstrom) and transition region (C II 1334/1335 Angstrom and Si IV 1394/1403 Angstrom). Slit-jaw images in four different passbands (C II 1330, Si IV 1400, Mg II k 2796 and Mg II wing 2830 Angstrom) can be taken simultaneously with spectral rasters that sample regions up to 130 arcsec x 175 arcsec at a variety of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to emission from plasma at temperatures between 5000 K and 10 MK and will advance our understanding of the flow of mass and energy through an interface region, formed by the chromosphere and transition region, between the photosphere and corona. This highly structured and dynamic region not only acts as the conduit of all mass and energy feeding into the corona and solar wind, it also requires an order of magnitude more energy to heat than the corona and solar wind combined. The IRIS investigation includes a strong numerical modeling component based on advanced radiative-MHD codes to facilitate interpretation of observations of this complex region. Approximately eight Gbytes of data (after compression) are acquired by IRIS each day and made available for unrestricted use within a few days of the observation.

astro-ph.SR↗

arXiv2012

Study of single-lobed circular polarization profiles in the quiet Sun

The existence of asymmetries in the circular polarization (Stokes V) profiles emerging from the solar photosphere is known since the 1970s. These profiles require the presence of a velocity gradient along the line of sight, possibly associated with gradients of magnetic field strength, inclination and/or azimuth. We have focused our study on the Stokes V profiles showing extreme asymmetry in the from of only one lobe. Using Hinode spectropolarimetric measurements we have performed a statistical study of the properties of these profiles in the quiet sun. We show their spatial distribution, their main physical properties, how they are related with several physical observables and their behavior with respect to their position on the solar disk. The single lobed Stokes V profiles occupy roughly 2% of the solar surface. For the first time, we have observed their temporal evolution and have retrieved the physical conditions of the atmospheres from which they emerged using an inversion code implementing discontinuities of the atmospheric parameters along the line of sight. In addition, we use synthetic Stokes profiles from 3D magnetoconvection simulations to complement the results of the inversion. The main features of the synthetic single-lobed profiles are in general agreement with the observed ones, lending support to the magnetic and dynamic topologies inferred from the inversion. The combination of all these different analysis suggests that most of the single-lobed Stokes V profiles are signals coming from magnetic flux emergence and/or submergence processes taking place in small patches in the photospheric of the quiet sun.

astro-ph.SR↗

arXiv2009

Twisted flux tube emergence from the convection zone to the corona II: Later states

3D simulations of magnetic flux emergence are carried out in a computational domain spanning the upper layers of the convection zone to the lower corona. We use the Oslo Staggered Code to solve the full MHD equations with non-grey and NLTE radiative transfer and thermal conduction along the magnetic field lines. In this paper we concentrate on the later stages of the simulations and study the evolution of the structure of the rising flux in the upper chromosphere and corona, the interaction between the emerging flux and the weak coronal magnetic field initially present, and the associated dynamics. The flux tube injected at the bottom boundary rises to the photosphere where it largely remains. However, some parts of the flux tube become unstable and expand in patches into the upper chromosphere. The flux rapidly expands towards the corona, pushing the coronal and transition region material aside, lifting and maintaining the transition region at heights greater than 5 Mm above the photosphere for extensive periods of time. The pre-existing magnetic field in the corona and transition region is perturbed by the incoming flux and reoriented by a series of high Joule heating events. Low density structures form in the corona while at later times a high density filamentary structure appears in the lower part of the expanding flux. The dynamics of these and other structures is discussed. While Joule heating due to the expanding flux is episodic, it increases in relative strength as fresh magnetic field rises and becomes energetically important in the upper chromosphere and corona at later times. Chromospheric, transition region and coronal lines are computed and their response to the perturbation caused by the expanding emerging flux is discussed.

astro-ph.SR↗

arXiv2009

Spicule-like structures observed in 3D realistic MHD simulations

We analyze features that resemble type i spicules in two different 3D numerical simulations in which we include horizontal magnetic flux emergence in a computational domain spanning the upper layers of the convection zone to the lower corona. The two simulations differ mainly in the preexisting ambient magnetic field strength and in the properties of the inserted flux tube. We use the Oslo Staggered Code (OSC) to solve the full MHD equations with non-grey and non-LTE radiative transfer and thermal conduction along the magnetic field lines. We find a multitude of features that show a spatiotemporal evolution that is similar to that observed in type i spicules, which are characterized by parabolic height vs. time profiles, and are dominated by rapid upward motion at speeds of 10-30 km/s, followed by downward motion at similar velocities. We measured the parameters of the parabolic profile of the spicules and find similar correlations between the parameters as those found in observations. The values for height (or length) and duration of the spicules found in the simulations are more limited in range than those in the observations. The spicules found in the simulation with higher preexisting ambient field have shorter length and smaller velocities. From the simulations, it appears that these kinds of spicules can, in principle, be driven by a variety of mechanisms that include p-modes, collapsing granules, magnetic energy release in the photosphere and lower chromosphere and convective buffeting of flux concentrations.

astro-ph.SR↗