The modelling of cool coronal loops can aid our understanding of processes in the upper solar atmosphere, and better understand their dynamics and evolution.
In this study, we explored the structure, and principal Lyman, Balmer, and MgII h&k emission of cool loops. This was achieved through the use of a 2D NLTE (i.e. departures from local thermodynamic equilibrium) cylindrical radiative...
What physical mechanisms heat the outer solar or stellar atmosphere to million-kelvin temperatures is a fundamental but long-standing open question. In particular, the solar corona in active-region cores contains an even hotter component reaching 10 MK, manifesting as persistent coronal loops in extreme ultraviolet and soft X-ray images, which imposes a stringent energy budget. Here, based on...
Sunspot formation is the primary manifestation of magnetic flux emerging from the convection zone into the solar atmosphere. Among the various features of sunspots, the penumbra is particularly intriguing due to several unresolved issues, such as the interpretation of its formation and decay processes and understanding its bolometric brightness.
Recent high-resolution spectropolarimetric...
One of the intriguing mechanism of the Sun is the formation of concentrated magnetic regions of opposite polarities on the surface called bipolar magnetic regions (BMRs). Such regions generally appear tilted with respect to the equatorial line. The thin flux tube model, employing the rising of magnetically buoyant flux loops twisted by the Coriolis force, is a popular paradigm to explain the...
Radio signals propagating via solar corona and solar wind are significantly affected by density fluctuations, impacting solar radio burst properties as well as the observations of sources viewed through the turbulent atmosphere. Using large-scale simulations of radio-wave transport, the radial profile of anisotropic density turbulence from the low corona to 1 au is explored. For the first...
Solar flares invariably begin with "hot onset" soft X-ray emission. This produces an initial horizontal branch in an [EM,T] diagnostic diagram (Jakimiec), a phase characterized by hot (5-20 MK) soft X-ray emission with continously growing emission measure. As detected by GOES, the hot onset may begin over up to 30 minutes
prior to the flare impulsive phase. This universal property has the...
Along with the increase in high-performance computing resources, the ability to conduct 3D simulations has made a difference to unveiling the topology of the magnetic structures during the eruption. Flux emergence has been proposed as a main trigger mechanism of CMEs Feynman & Martin(1995). The emergence of magnetic flux can reconnect with an existing, current-carrying flux rope and lead to an...
The Ca II 8542 line forms in the lower to middle solar chromosphere. Its sensitivity to magnetic fields as well as the accessibility to ground-based telescopes make it a preferred line for chromospheric diagnostics. The spatially averaged spectra of this line show a red-asymmetry in the line core which is often indicated by a line bisector that has an "inverse C-shape". Leenaarts et al. (2014)...
The polar magnetic field in the Sun is an important aspect of the solar dynamo process for predicting future solar cycles. However, systematic measurements of this polar field have only been available since 1976 at the Wilcox Solar Observatory (WSO). Prior to 1976, there was a lack of direct information on polar magnetic fields, leading people to utilize various proxies such as polar faculae...
A detailed understanding the structure and dynamics of the chromosphere is important to understand the heating of the solar atmosphere. The local magnetic field couples the turbulent convection zone to the atmosphere and provides the energy flux which heats the atmosphere. The study of the chromosphere is complicated by it's highly dynamic nature, additionally the radiative processes must be...
Lim et al. (2023) have recently proposed that the slope ($\delta$) of the power law distribution between the energy flux and oscillation frequency could determine whether high-frequency transverse oscillations give a dominant contribution to the heating ($\delta$<1). Using the meta-analysis of decayless transverse oscillations, it has been found that high-frequency oscillations could play a...
We present results of the behaviour of the solar differential rotation during solar cycle No. 24 derived from the Kanzelhöhe data set (Kanzelhöhe Observatory for Solar and Environmental Research, University of Graz, Austria). Sunspot groups and their properties (umbra, penumbra, size, and position) were identified by morphological image processing of Kanzelhöhe white light images for the time...
Various dynamical processes occur in the solar atmosphere, significantly contributing to its thermal balance. Observations and simulations have particularly highlighted the importance of waves and magnetic reconnection in the chromosphere, which provide the necessary energy to counterbalance radiative cooling. However, the relative contributions of different processes in various solar regions...
Using a simplified kinetic plasma model, we show that a transition region and a million-Kelvin corona can form thanks to fast, short-lived temperature fluctuations in the chromosphere. The proposed mechanism works if such activity occurs on sub-second timescales, which however are unresolved in current observations.
We briefly outline the model and then discuss two scenarios in which...
In a quiet region, a variety of convection (granulation)-driven phenomena at a tiny spatial scale are observed. For their understanding, it is important to derive the vector of the velocity and magnetic field. One of the effective approaches to study the phenomena is to take advantage of the stereoscopic configuration between Solar Orbiter (SO)/ Polarimetric Helioseismic Imager (PHI) and...
Understanding the mechanism behind coronal heating remains a fundamental challenge in solar physics. Above small-scale bipolar regions we observe Coronal Bright Points (CBPs) in extreme-UV coronal emission. We analyze 346 CBPs track their lifetimes, shapes, polarities, merging behavior, etc. to select a typical CBP for a 3D MHD simulation.
Most CBPs show magnetic some flux cancellation. The...
Close-to-limb magnetic field observations face challenges due to foreshortening, reduced light levels, the influence of the observation angle on the radiative transfer, among other effects. These factors contribute to increased uncertainty in the inferred magnetic field, impacting studies involving magnetograms.
To address these limitations, we can leverage data from a second vantage...
Since its launch in February 2020, Solar Orbiter (SO) has been providing high-quality data from the many layers of the solar atmosphere. The Polarimetric and Helioseismic Imager onboard SO (SO/PHI) is a spectropolarimeter scanning the Fe I line at 617 nm, the same line sampled by SDO/HMI and many other on-ground instruments providing data of the solar photosphere. A first comparison of the...
The eleven-year solar activity cycle is known to affect solar acoustic oscillations; higher activity is correlated with an increase in mode frequencies and a decrease in their lifetimes. Activity related frequency shifts have also been observed in other stars, but are difficult to measure mode by mode. Measurements seismic travel times provide an alternate method which is robust to noise ...
We presents a comparison of plasma dynamics in Coronal Holes (CHs) and Quiet Sun (QS) through observations and 2.5D MHD flux emergence simulations. We observe these regions in chromospheric and transition region lines of IRIS as a function of the underlying photospheric magnetic field (|B|). We find excess intensity (blue, redshifts) in QS(CH) with |B|. We observe persistent upflows,...
Closed magnetic loops make up a large part of the magnetically closed corona of the Sun and other stars.
Coronal loops come in different shapes and sizes.
Loop length, magnetoconvection at the footpoints and numerical resolution influence loop properties such as temperature, density and velocities.
These parameters in turn influence observable quantities such as emission intensity and the...
Flares and jets are explosive phenomena driven by magnetic reconnection in the solar atmosphere. We present a comprehensive study combining observational analysis and numerical simulations to elucidate the intricate structures and processes underlying these events. Utilizing SDO/HMI vector magnetogram data, we performed a data-constrained simulation of a C1.3 class flare observed in an active...
Coronal rain can be a key indicator of coronal heating taking place. To resolve
the coronal heating problem it behoves us to fully investigate this link across
the full disk of the Sun. There is no lack of observational data, but currently
this data is inadequate for a complete analysis of the phenomenon to be carried
out. The AIA 304 channel provides the best dataset for coronal rain...
The relationship between the total magnetic flux of active regions (ARs) and the area of their enclosed sunspots serves as a fundamental property of ARs. Notably, deducing the historical magnetic flux of the brightening magnetic features on the Sun, i.e., faculae and networks, is compelling for understanding the long-term variations of the solar surface magnetic flux. It is also significant...
Converging flows are visible around Bipolar magnetic regions (BMRs) on the solar surface, according to observations. Average flows are created by these inflows combined, and the strength of these flows depends on the amount of flux present during the solar cycle. In models of the solar cycle, this average flow can be depicted as perturbations to the meridional flow. Here, we study the effects...
The data transmitted by Parker Solar Probe (PSP) from the young solar wind build on the puzzle of electron properties with many important pieces. Of particular interest are the suprathermal populations responsible for the transport of heat flux in the solar wind. We refer to both suprathermal components, the so-called halo and the strahl or beam component, whose trends suggested by previous...
Mass drainage is frequently observed in solar filaments. During filament eruptions, falling material most likely flows along magnetic field lines, which may provide important clues for the magnetic structures of filaments. Here we study three filament eruptions exhibiting significant mass draining, often manifested as falling threads at a constant speed ranging between 50--300 km s$^{-1}$. We...
The expanding solar wind plasma ubiquitously exhibits anisotropic non-thermal particle velocity distributions. Typically, proton Velocity Distribution Functions (VDFs) show the presence of a core and a field-aligned beam. Novel observations made by Parker Solar Probe (PSP) in the innermost heliosphere have revealed new complex features in the proton VDFs, namely anisotropic beams that...
The heat-flow fluctuations along the quiet Sun convective pattern are studied in data provided by high-resolution observations and simulations. Using the methods of stochastic thermodynamics it is shown that heating and cooling of the photospheric flows obey a remarkable thermal relaxation asymmetry which was recently discovered in laboratory experiments.
We investigate several mechanisms that may produce abundance variations in the solar atmosphere, called as the First Ionization Potential (FIP) effect. We develop and exploit a multi-specie 1-D model of the solar atmosphere (called IRAP’s Solar Atmospheric Model: ISAM) that solves, along a given magnetic field line, the transport of neutrals, electrons and charged particles from the...
Coronal hole plumes, largely radial ray-like structures located in coronal holes, are often the targets of studies of magnetohydrodynamic waves and of solar wind origins in the corona. The plume bases seem to be very active with many small-scale transients observed, which are likely important to the formation and evolution of plumes and could contribute to the solar wind. We study three plumes...
The origin of the slow solar wind remains an open issue. One proposed explanation is that upflows at the border of active regions can be a source of the slow solar wind. The processes generating these upflows are not fully understood. Three potential mechanisms have been proposed: (I) reconnection between closed coronal loop and open magnetic field lines in the lower corona, (II) reconnection...
The Solar Atmosphere is subject to a number of oscillatory motions. Magnetic flux tubes acts as wave guides from the lower atmosphere to the upper. In a uniform plasma, there are three distinct magnetohydrodynamic (MHD) wave modes: Alfvén and fast and slow magnetoacoustics waves. In a non-uniform plasma, like the solar atmosphere, these wave modes no longer decouple. It follows that...
Twisted magnetic fields in the solar chromosphere are thought to give rise to a plethora of MHD waves and flows, enabling mass and energy channelling from the photosphere to the corona. Here we report on the statistical properties of observations of waves and flows in an apparently stable but relatively large-scale spiral structure (herein referred to as a “giant spiral”), close to disk...
The origin and formation of the slow solar wind remain an open question in solar physics. One possible scenario is that the slow solar wind may arise from coronal hole boundaries (CHBs) via interchange reconnection. This process also dominates the small-scale evolution of coronal hole boundaries. In this study, we investigate the small-scale evolution of magnetic field and plasma properties at...
This study, focused on exploring the properties of Bright Points (BPs) in different regions of the Sun, with a particular emphasis on their oscillatory behavior. They developed a machine learning model to identify and analyze BPs in solar images, achieving a 78% accuracy in BP identification, then used wavelet and Fourier analysis to investigate the oscillatory behavior of the identified...
Understanding the mechanisms of high-energy particle production and propagation from the Sun is crucial for advancing solar physics and enhancing space weather prediction. This work aims to elucidate electron acceleration processes within the solar atmosphere and their journey into the heliosphere. We use data from advanced radio telescopes, such as the Low-Frequency Array and Nançay...
The elusive solar corona, when observed in white light, presents contributions from two main components of scattered photospheric light: the K-corona, due to electrons, and the F-corona, due to dust. While the K-corona corresponds to the "true corona" and displays structuring in the form of helmet streamers, pseudostreamers, coronal holes, and plumes, the diffuse F-corona dominates the...
Solar active regions (ARs), which are formed by flux emergence, serve as the primary sources of solar eruptions. However, the specific physical mechanism that governs the emergence process and its relationship with flare productivity remains to be thoroughly understood. In this study, we examined 136 emerging ARs, focusing on the evolution of their magnetic helicity and magnetic energy during...
The equilibrium of coronal structures like loops in active regions is determined by a balance between the inward magnetic tension and the outward magnetic pressure gradient forces. The dissipation of the magnetic energy from the volume below the loops after a flare causes the lack of magnetic support, hence a contraction or implosion of the coronal loops. Such a contraction is also observed...
At low coronal temperatures of approximately 1 MK, distinct regions show emission at a level significantly below the quiet Sun. Prominent examples are coronal voids in the quiet Sun and dark halos (also referred to as canopies or moats) surrounding active regions. Several models have been proposed, yet the mechanism behind the formation of dark halos remains not fully understood.
Solar...
Solar flares can release coronal magnetic energy explosively and may impact the safety of near-Earth space environments. Their structures and properties on the macroscale have been interpreted successfully by the generally accepted 2D standard model, invoking magnetic reconnection theory as the key energy conversion mechanism. Nevertheless, some momentous dynamical features discovered by...
Magnetohydrodynamic waves are ubiquitously detected in the highly structured solar atmosphere. At the same time, the solar atmosphere is also a highly dynamic plasma environment, giving rise to flows of various magnitudes, which can lead to instability of the waveguides. Recent studies have not only introduced waveguide asymmetry to generalize “classical” symmetric modelling of the fine...
Oscillations around the X-points play an important role in corona plasma heating. In this paper we investigate resonance absorption around X points. We have found analytical solutions for the Alfven continuum mode in the presence of a guide field. We also drive a jump conditions in the flux coordinates. Using these conditions, we obtain the dispersion relation and solve it numerically to find...
Reduced order modelling (ROM) plays an important role in the descriptions of different plasma environments such as heliosphere, solar wind and beyond. ROMs can be obtained via analytical closures; however, such approaches are limited when distribution functions are far from Maxwellian and/or in weaker guide fields. To push the envelope of ROMs in plasmas we apply machine learning frameworks...
Magnetohydrodynamic (MHD) waves have been utilised for decades for probing plasmas and increasing understanding of dynamic processes within the solar atmosphere, a technique called MHD seismology. Propagating slow magnetoacoustic (MA) waves are particularly valuable for MHD seismology due to their persistence, propagation along magnetic field lines, and their links to the coronal heating...
We present comprehensive tables of Net Radiative Cooling Rates (NRCR) in cool solar plasma with prominence-like properties. These NRCR are based on the 1D non-LTE radiative transfer modelling of prominences in the transitions of 5-level plus continuum hydrogen, Mg II and Ca II ions. These atomic transitions are the dominant contributors to the radiative energy budget of prominence-like...
Coronal loops are the basic structures of the solar corona resulting from the confinement of the multi-thermal coronal plasma in magnetic flux tubes.
Improving their modeling could help in understanding the physical processes involved in the formation and evolution of loops, and the mechanisms of energy transfer in the solar atmosphere.
In this work we performed several direct numerical...
Magnetic loops are widely observed structures in the solar transition region and corona. As closed magnetic flux tubes, they can act as important wave guides for MHD waves, particularly transverse waves/oscillations. In recent coronal observations, transverse oscillations in small magnetic loops have been frequently studied, uncovering two different types of decayless kink oscillations. The...
Solar flares can induce many changes in the Sun’s atmosphere, primarily due to the energy deposited in the lower atmosphere by particles accelerated from a magnetic reconnection site in the corona. The majority of this energy is deposited in the chromosphere, although the method of this energy transport is not yet agreed on. Radiation hydrodynamics models predict that an electron beam via the...
Magnetic reconnection is a fundamental physical process that converts magnetic energy into plasma energy and particle energy in various astrophysical phenomena. In this talk, I will show a unique dataset of a solar flare where a continually stretched current sheet formed various plasmoids. EUV images captured reconnection inflows, outflows, and particularly the recurring plasma blobs...
The solar corona is extremely hot with temperatures above 1 MK. In the decades after this discovery, many different heating methods have been developed to explain the high temperatures. A prominent category of these heating models is direct current (DC) heating, where the dissipation of strong currents, created by the tangling and braiding of magnetic field due to the convective motions in the...
Active region moss forms at the footpoints of 3--10 MK hot loops. Observations with the High-resolution Coronal Imager (Hi-C) revealed some moss regions exhibiting temporal variability on timescales of 30s. This rapid moss variability is hypothesized to be an indirect evidence for the nanoflare heating model of coronal loops. However, since Hi-C was a sounding rocket mission, the observations...
Bipolar light bridges (BLBs) are bright features in sunspots located between two umbrae with opposite magnetic polarity. Recent observations revealed intriguing cases of BLBs with very strong magnetic fields of the order of 8.2 kG, which is at least twice the typical values measured in sunspot umbrae. Since these observations were only a few, it is a question of whether BLBs with...
Spicules are the thin, hair/grass-like structures prominently observed at the chromospheric solar limb. It is believed that fibrils and Rapid Blue and Red Excursions (RBEs and RREs; collectively referred to as REs) correspond to on-disk counterparts of type I spicules & type II spicules, respectively. Our investigation focuses on observing the response of these REs alongside similar spectral...
Abstract: Recurrent jets are regarded as one of the crucial processes for the periodic release of magnetic free energy through intermittent magnetic reconnections. In this talk, we will present a detailed analysis of the dynamic, thermal, and magnetic characteristics and evolution of a typical anemone jet amid a series of recurrent eruptions at the edge of the active region 13102. This jet...
The formation of penumbrae has been studied by many authors and, yet, many questions remain to be answered. Penumbra formation is a target of opportunity that, due to its relatively fast development, is not common to observe with very high spatial resolution. In this work we present ground-based spectropolarimetric observations of a forming sunspot on the NOAA 11024 recorded with the...
Oscillatory Reconnection is a fundamental relaxation mechanism, characterised by changes in magnetic connectivity, the oscillatory nature of which requires no external periodic driving force to be sustained. This process has been one of the proposed mechanisms behind phenomena, such as quasi-periodic pulsations (QPPs). Its manifestation through the interaction of the ubiquitous waves with null...
Reconnection is a fundamental process that is at the heart of dynamic events such as solar flares. Despite these phenomena being time-dependent, they are often explained using steady-state theoretical reconnection models such as Sweet-Parker and Petschek. In this presentation I will compare the steady-state models of reconnection with a high-resolution simulation of oscillatory reconnection; a...
The recent discovery of ubiquitous switchbacks, localized magnetic deflections in the nascent solar wind, by the Parker Solar Probe (PSP) has sparked interest in uncovering their origins. A prominent theory suggests these switchbacks originate in the lower corona through magnetic reconnection processes, closely linked to solar jet phenomena. Jets are impulsive phenomena, observed at various...
Alfvénic waves are one of the most promising candidates for heating the solar corona and accelerating the solar wind in polar coronal holes. These are observed as the transverse motion of spicules (jets elongated along the magnetic field lines) in the chromosphere. However, whether sufficient wave energy is carried to the corona remains unclear because the waves in the chromosphere suffer from...
We analyzed the properties of the magnetic field of a solar sunspot, which was closely associated with a solar eruption in active region AR 13079 observed on August 13, 2022, using modern computational techniques. Spektropolarimetric observations were obtained using the infrared spectrograph GREGOR (GRIS) on the 1.5-meter GREGOR Telescope. Our goal was to examine the magnetic and dynamic...
The solar chromosphere consists of poorly understood, dynamic fine structures. In this work we use the MURaM code, which has recently been updated to include the NLTE physics required to treat the chromosphere. Our flux emergence simulations of an enhanced network element show finely structured chromospheric features, akin to the rapid red and blue shifted excursions (RREs and RBEs) observed...
Quasi-periodic oscillations (QPOs) observed in the solar chromosphere and transition region during flares offer valuable insights into the atmospheric response to sudden energy releases and the evolution of the magnetic field. We have analyzed an M-6.5 class flare observed by the Interface Region Imaging Spectrograph (IRIS) with emphasis on the QPOs in the Doppler velocity measured in the Si...
In the solar atmosphere, radiation plays an important role in the energy balance. Extinctions or emissions of photons from transitions between atomic energy levels can either heat or cool the local atmosphere, and their contributions are expressed as the radiative flux divergence, referred to as the radiative losses. Detailed calculations could be computationally expensive, especially in the...
The emergence and evolution of solar granulation provide important insights into photospheric plasma dynamics. We investigate the temporal evolution of convective cells both in quiet and magnetised regions, tracking their evolution over periods of approximately 30 minutes.
We employed a pattern-recognition algorithm based on multiple intensity thresholds for solar granulation segmentation,...
Many studies of quasi-periodic pulsations in solar flares have identified characteristic periods in the 5 – 300s range. These phenomena are crucial to understand as they relate to fundamental energy release on the Sun. Due to observational constraints it is unclear whether the periods of quasi-periodic pulsations extend down into the < 5s period regime. The Fermi Gamma-ray Burst Monitor...
During its first close encounter of 2023, the Solar Orbiter spacecraft was magnetically connected to different areas within an active region-coronal hole (AR-CH) complex. As the spacecraft was close to the Earth-Sun line at the time, IRIS and Hinode EIS were able to provide coordinated observations of the AR-CH complex. These complementary datasets provide the perfect opportunity to...
The presence of energetic electrons in the heliosphere is associated with solar eruptions, but details of the acceleration and transport mechanisms are still unknown. We explore how electrons interact with shock waves under the assumptions of stochastic shock drift acceleration (SSDA). Consideration of the shock wave parameter space, such as shock speed, shock obliquity, shock thickness, and...
It is widely accepted that eruptive phenomena on the Sun are related to the solar magnetic field, which is closely tied to the observed magnetic concentrations (MCs). Therefore, studying MCs is critical in order to understand the origin and evolution of all forms of solar activity. In this paper, we investigate the statistics of characteristic physical parameters of MCs during a whole solar...
We use statistical tools to analyse data from the Solar Dynamics Observatory Helioseismic and Magnetic Imager to determine the distribution of the magnetic flux of photospheric magnetic features and its variation over a full solar cycle.
We use statistical figures of merit to test how well different types of probability distribution function represent the magnetic flux distribution...
Kanzelhöhe Observatory for Solar and Environmental Research (KSO) provides daily multispectral synoptic observations of the Sun. The synoptic observations allow us to study the subsurface dynamics of the Sun, such as the profile of solar differential rotation, meridional and zonal flows, and their variability, which are crucial for understanding the solar dynamo. Our goal is to extend the...
We analyze series of Dopplergrams from MWO (1967-2012), GONG (2001-2022), and SDO/HMI (2010-2022) to characterize the temporal variations of the high-latitude solar inertial mode with azimuthal order $m=1$. This mode has an amplitude of 10-20 m/s, making it the strongest among all the observed modes in the inertial frequency range. We will present measurements of the mode's power and...
We present unique results of a recent study of bright eruptive prominence embedded in the core of a CME observed by the Metis coronagraph on board the Solar Orbiter on April 25-26, 2021. Metis provides simultaneous imaging in the hydrogen Lyman alpha line and in the VL. Triangulation is used to estimate the de-projected height and velocity of the structure. Based on previous studies of the...
This study aims to reveal the heating mechanism in coronal loops by observationally deriving the relation among the heating flux $F_\rm{H}$, the magnetic field $B_\rm{base}$, and the loop half-length $L_\rm{half}$. While the previous studies investigated the heating mechanism assuming some parameters (e.g., heating scale height), this study directly derives the parameters from the...
As seen in most textbooks of astrophysics, most astronomical bodies such as main sequence stars have been investigated only by Newtonian gravity. This is presumably based on a belief that Newtonian physics could be sufficient to extract important physics of most astronomical bodies except compact stars and General Relativity would be too precise to be suitable.
In this talk, I will...
Solar radio spikes observed as narrow-bandwidth, sub-second bursts are indicative of rapid, small-scale energy release in the corona, yet localising the site of electron acceleration is a significant challenge. Using millisecond imaging from the LOw Frequency ARray (LOFAR) between 30-45 MHz, we present a statistical analysis of solar radio spikes associated with a coronal mass ejection (CME)....
The solar chromosphere and transition region (TR) play an important role in coupling the dense, 6000K photosphere to the tenuous, million degree corona. As the plasma beta changes dramatically over these layers, ascertaining the processes that maintain their thermal structure remains a fundamental problem in solar physics. By combining observations from the 50-cm Multi-Application Solar...
SOLAR-C and MUSE are among the next generation solar missions, with launch dates in 2028 and 2027 respectively. Those mission will carry two complementary instruments providing each high resolution spectroscopy in the UV and EUV.
The EUV High-throughput Spectroscopic Telescope (EUVST) onboard SOLAR-C will obtain high temporal, spectral, and spatial resolution spectra of the Sun over a wide...
Non-LTE radiative transfer in 2D was performed for the hydrogen plasma of a loop-like structure within eruptive prominence obtained by 3D MHD simulation. The simulation made by Fan & Liu (2019) shows evolution of a prominence from quasi-equilibrium to the onset of eruption of a twisted, prominence forming coronal magnetic flux rope which underlays a coronal streamer. The 180th time step of the...
Coronal bright points are systems of loops that connect small bipoles in the magnetic network of the quiet Sun.
While a bright point as a whole might persist for several hours, individual loops within it evolve on timescales of minutes.
Capturing their atmospheric signatures, that span from the ultraviolet to X-rays, requires simultaneous observations over a broad range of plasma...
In this contribution we use millimeter wavelength diagnostic to test a new model of the solar chromosphere resembling an enhanced network region. The model is based on the recently developed chromospheric extension of the non-equilibrium version of the radiative-MHD code MURaM. We synthesized radio brightness at the operational wavelengths of the Atacama Large Millimeter/Submillimeter Array...
Coronal loops, the arching structures filled with magnetically confined million Kelvin hot plasma, are the prominent features of the solar atmosphere. These loops are best observed in the extreme ultraviolet (EUV) and X-ray wavelengths. Coronal loop emission generally traces the magnetic field lines in the upper solar atmosphere. Thus probing their spatial morphology and evolution will help us...
Sunspots are intense regions of magnetic flux that are rooted deep below the photosphere. It is well established that sunspots host magnetohydrodynamic waves, with numerous observations showing a connection to the internal acoustic or p-modes of the Sun. The p-modes are fast waves below the equipartition layer and are thought to undergo a double mode conversion as they propagate upwards into...
Coronal loops are known to host Alfvén waves propagating in the corona from the lower layers of the solar atmosphere and because of their internal structure, phase-mixing is likely to occur. The structure of the coronal loop could be significantly affected by the thermodynamic feedback of the heating generated by phase-mixing. However, this phenomenon can be sensitive to the period of the...
The feasibility of restoration of spectrograph data was first demonstrated by Keller and Johannesson [1995] based on a speckle-based method. In van Noort [2017] this method was revisited using an MFBD based approach on data acquired with the SST. This new approach allows for the restoration of spectro-polarimetric data over large FOVs with a spatial resolution that can compete with that of...
Bright heads of penumbral filaments, penumbral grains (PGs), show apparent horizontal motions inward, toward the umbra, or outward, away from the umbra. Using high-resolution spectropolarimetric observations and numerical simulations of sunspot penumbrae, we aim to prove whether the direction of these motions is related to the inclination of the penumbral magnetic field.
Magnetic-field...
The changing magnetic field in solar flares has a complex association with the UV emissions of the flare ribbons. These ribbons appear as visual markers indicating the sites where magnetic field lines go through a coronal reconnection processes, which has been determined to be the driving process of flare formation. However, this process is not entirely clear. We aimed to investigate the...
The origin of the sudden deflections of the magnetic field, known as magnetic switchbacks, is still hotly debated. These structures, which are omnipresent in the in situ observations made by Parker Solar Probe (PSP), are likely to have their seed in the lower corona. There is an increasing consensus that small-scale energetic magnetic field reconnection plays a crucial role in establishing the...
On October 28, 2021 the first X-class solar flare of Solar Cycle 25 occurred in active region NOAA AR 12887. It produced the rare event of ground-level enhancement of the solar relativistic proton flux and a global extreme ultraviolet (EUV) wave, along with a fast halo coronal mass ejection (CME) as seen from Earth's perspective. A few hours before the flare, a slower CME had erupted from a...
It is well known that the dominant frequency of oscillations in the solar photosphere is at $\approx$3 mHz, which is the result of global resonant modes pertaining to the whole stellar structure. However, analyses of the horizontal motions of nearly $1$ million photospheric magnetic elements spanning the entirety of solar cycle 24 has revealed an unexpected dominant frequency $\approx$5 mHz,...
The Hα line is widely used to study solar chromosphere, but polarimetric studies to infer magnetic fields are scarce. This is partly due to no polarimetric studies of Hα line utilizing 3-D radiative transfer, and earlier 1-D radiative transfer studies suggested a significant contribution of the photospheric fields. By analyzing spectropolarimetric data of a small pore simultaneously recorded...
This study investigates the damping characteristics of Doppler velocity oscillations in solar bright points (BPs) using spectral analysis and deep learning techniques.
This study analyzed Doppler shifts in the solar spectrum captured by the Interface Region Imaging Spectrograph (IRIS), focusing on periodic oscillations within BPs. The damping of red and blue Doppler shifts and employed deep...
Recent high-resolution solar observations have unveiled the presence of small-scale loop-like structures in the lower solar atmosphere, often referred to as unresolved fine structures, low-lying loops, and miniature hot loops. These structures undergo rapid changes within minutes, and their formation mechanism has remained elusive. In this study, we conducted a comprehensive analysis utilizing...
Solar jets, characterized by small-scale plasma ejections along open magnetic field lines or the limbs of large-scale coronal loops, play a crucial role in the dynamics of the solar atmosphere. They are often associated with other solar activities, including campfires, filament eruptions, coronal bright points, flares, and coronal mass ejections. Although spectral and EUV images have been...
Plasma upflows with a Doppler shift exceeding 20 km/s at active region (AR) boundaries are considered potential sources of nascent slow solar wind. These upflows are often located at the footpoints of large-scale fan-like loops, showing temperature-dependent Doppler shifts from the transition region to the lower corona. In this study, we identified two upflow regions in the vicinity of an...
Magnetic bright points on the solar photosphere mark the footpoints of kilogauss magnetic flux tubes extending toward the corona. Convective buffeting of these tubes is believed to excite magnetohydrodynamic waves, which can propagate to the corona and there deposit heat. Measuring wave excitation via bright-point motion can thus constrain coronal and heliospheric models, and this has been...
Solar atmospheric heating inferred from observations is known to be higher than the equilibrium rate of a static atmosphere, but it is unclear how the heating is supplied. Two leading theories are standing out as the most likely candidates to balance the high radiative losses of the solar atmosphere: heating by waves (AC heating), and magnetic reconnection (DC heating). Understanding AC...
We present observations of small- to intermediate-scale energy release events occurring in the solar atmosphere, investigated using multiwavelength, multi-instrument high-resolution data. Ultraviolet (UV) observations acquired by satellites, along with complementary simultaneous spectro-polarimetric measurements by ground-based telescopes, allow us to shed light on the dynamic interplay...
Vortex flows in the solar photosphere are ubiquitous and are thought to inject energy into the upper solar atmosphere in the form of Poynting flux. However, observing photospheric intensity vortices is challenging due to their small size and the fact that the flow field is primarily parallel to the plane-of-sky. Despite this, a large number of photospheric intensity vortices have been observed...
The solar chromosphere is a highly dynamic layer governed by magnetic forces. Models and observations alike have difficulties in their analysis and interpretation. For instance, what mechanism is responsible for heating the chromosphere needs yet to be determined. Chromospheric plasma contains a significant amount of neutral particles. For phenomena operating at timescales significantly larger...
One of the most stunning discoveries of the Parker Solar Probe mission is the wealth of kinetic scale processes occurring in the low solar atmosphere (Bale et al. 2019). In this work (Afify et al. 2024), we investigate, with a combination of theoretical and numerical tools, the ion-acoustic waves observed by the Parker Solar Probe near the Sun (Mozer et al. 2021, 2023; Kellogg et al. 2024)....
Solar coronal waves frequently appear as bright disturbances that propagate globally from the eruption center in the solar atmosphere, just like the tsunamis in the ocean on Earth. Theoretically, coronal waves can sweep over the underlying chromosphere and leave an imprint in the form of Moreton wave, due to the enhanced pressure beneath their coronal wave front. Despite the frequent...
