We measure the effects of non-isotropic thermal conduction on generation of solar chromospheric jets through numerical simulations carried out with the use of one fluid MHD code MAGNUS. Following the work of Srivastava et al. (2018), we consider the atmospheric state with a realistic temperature model and generate the ejection of plasma through a gas pressure driver operating in the top chromosphere. We consider the magnetic field mimicking a flux tube and perform parametric studies by varying the magnetic field strength and the amplitude of the driver. We find that in the case of thermal conduction the triggered jets exhibit a considerably larger energy and mass fluxes and their shapes are more collimated and penetrate more the solar corona than for the ideal MHD equations. Low magnetic fields allow these jets to be more energetic, and larger magnetic fields decrease the enhancement of mass and energy due to the inclusion of the thermal conductivity.
We have studied the chromospheric evaporation flow during the impulsive phase of the flare by using the Hinode/EIS observation and 1D hydrodynamic numerical simulation coupled to the time-dependent ionization. The observation clearly shows that the strong redshift can be observed at the base of the flaring loop only during the impulsive phase. We performed two different numerical simulations to reproduce the strong downflows in FeXII and FeXV during the impulsive phase. By changing the thermal conduction coefficient, we carried out the numerical calculation of chromospheric evaporation in the …
{Chromospheric evaporation is a key process in solar flares that has extensively been investigated using the spectroscopic observations. However, direct soft X-ray (SXR) imaging of the process is rare, especially in remote brightenings associated with the primary flares that have recently attracted dramatic attention.} {We intend to find the evidence for chromospheric evaporation and figure out the cause of the process in sympathetic coronal bright points (CBPs), i.e., remote brightenings induced by the primary CBP.} {We utilise the high-cadence and high-resolution SXR observations of CBPs fro…
Magnetic reconnection in the corona results in contracting flare loops, releasing energy into plasma heating and shocks. The hydrodynamic shocks so produced drive thermal conduction fronts (TCFs) which transport energy into the chromosphere and drive upflows (evaporation) and downflows (condensation) in the cooler, denser footpoint plasma. Observations have revealed that certain properties of the transition point between evaporation and condensation (the "flow reversal point" or FRP), such as temperature and velocity-temperature derivative at the FRP, vary between different flares. These prope…
We investigate the effect of coronal temperature on the formation process of solar chromospheric jets using two-dimensional magnetohydrodynamic simulations of the region from the upper convection zone to the lower corona. We develop a new radiative magnetohydrodynamic code for the dynamic modeling of the solar atmosphere, employing a LTE equation of state, optically thick radiative loss in the photosphere, optically thin radiative loss in the chromosphere and the corona, and thermal conduction along the magnetic field lines. Many chromospheric jets are produced in the simulations by shock wave…
In solar physics, a severe numerical challenge for modern simulations is properly representing a transition region between the million-degree hot corona and a much cooler plasma of about 10000 K (e.g., the upper chromosphere or a prominence). In previous 1D hydrodynamic simulations, the transition region adaptive conduction (TRAC) method has been proven to capture aspects better that are related to mass evaporation and energy exchange. We aim to extend this method to fully multidimensional magnetohydrodynamic (MHD) settings, as required for any realistic application in the solar atmosphere. Be…
Recent observational and numerical studies show a variety of thermal structures in the solar chromosphere. Given that the thermal interplay across the transition region is a key to coronal heating, it is worth investigating how different thermal structures of the chromosphere yield different coronal properties. In this work, by MHD simulations of Alfvén-wave heating of coronal loops, we study how the coronal properties are affected by the chromospheric temperature. To this end, instead of solving the radiative transfer equation, we employ a simple radiative loss function so that the chromosphe…
Magnetic energy released in the corona by solar flares reaches the chromosphere where it drives characteristic upflows and downflows known as evaporation and condensation. These flows are studied here for the case where energy is transported to the chromosphere by thermal conduction. An analytic model is used to develop relations by which the density and velocity of each flow can be predicted from coronal parameters including the flare's energy flux $F$. These relations are explored and refined using a series of numerical investigations in which the transition region is represented by a simpli…
The presence of the magnetic field is critical to transport energy through the solar atmosphere. The new generation of telescopes will provide new insight into how the magnetic field arrives into the chromosphere and its role in the energy balance of the solar atmosphere. We have used a 3D radiative MHD numerical model of the solar atmosphere with high spatial resolution (4~km) calculated with the Bifrost code. This code solves the full MHD equations with non-grey and non-LTE radiative transfer and thermal conduction along magnetic field lines. The model shows how the lower chromosphere in the…
Observations reveal a correspondence between chromospheric type II spicules and bright upwardly moving fronts in the corona observed in the EUV band. However, theoretical considerations suggest that these flows are unlikely to be the main source of heating in coronal magnetic loops. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes, and the possible production of emission in the EUV band. We simulate the propagation of a dense $10^4$ K chromospheric jet upwards along a coronal loop, by means of a 2-D cylindrical MHD model, including gravity, radi…
We present results from the first self-consistent multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma. We simulate two dimensional magnetic reconnection in a Harris current sheet with a numerical model which includes ion-neutral scattering collisions, ionization, recombination, optically thin radiative loss, collisional heating, and thermal conduction. In the resulting tearing mode reconnection the neutral and ion fluids become decoupled upstream from the reconnection site, creating an excess of ions in the reconnection region and therefore an ion…
In models of fast magnetic reconnection, flux transfer occurs within a small portion of a current sheet triggering stored magnetic energy to be thermalized by shocks. When the initial current sheet separates magnetic fields which are not perfectly anti-parallel, i.e. they are skewed, magnetic energy is first converted to bulk kinetic energy and then thermalized in slow magnetosonic shocks. We show that the latter resemble parallel shocks or hydrodynamic shocks for all skew angles except those very near the anti-parallel limit. As for parallel shocks, the structures of reconnection-driven slow …
In the classical flare picture, hard X-ray emission from the chromosphere is succeeded by soft-X-ray emission from hot plasma in the flare loop, the soft X-ray emission being a direct consequence of the impact of the non-thermal particle beam. However, observations of events exist in which a pronounced increase in soft X-ray emission is observed minutes before the onset of the hard X-ray emission. Such pre-flare emission clearly contradicts the classical flare picture. For the first time, the pre-flare phase of such solar flares is studied in detail. We want to explain the time evolution of th…
Context. Theoretical arguments and numerical simulations of radiative shocks produced by the impact of the accreting gas onto young stars predict quasi-periodic oscillations in the emitted radiation. However, observational data do not show evidence of such periodicity. Aims. We investigate whether physically plausible perturbations in the accretion column or in the chromosphere could disrupt the shock structure influencing the observability of the oscillatory behavior. Methods. We performed local 2D magneto-hydrodynamical simulations of an accretion shock impacting a chromosphere, taking optic…
We report on observations of a solar jet propagating along coronal loops taken by the Solar Dynamics Observatory (SDO), the Interface Region Imaging Spectragraph (IRIS) and 1-m New Vacuum Solar Telescope (NVST). The ejecta of the jet consist of multi-thermal components and propagate with a speed greater than 100 km/s. Brightenings are found in the remote footpoints of the coronal loops having compact and round-shape in the Halpha images. The emission peak of the remote brightening in the Atmospheric Imaging Assembly (AIA) 94 Åpassband lags 60 s behind that in the jet base. The brightenings in …
Dissipation of magnetohydrodynamic (MHD) wave energy has been proposed as a viable heating mechanism in the solar chromospheric plasma. Here, we use a simplified one-dimensional model of the chromosphere to theoretically investigate the physical processes and the spatial scales that are required for the efficient dissipation of Alfvén waves and slow magnetoacoustic waves. We consider the governing equations for a partially ionized hydrogen-helium plasma in the single-fluid MHD approximation and include realistic wave damping mechanisms that may operate in the chromosphere, namely Ohmic and amb…
In this work we describe our implementation of a thermodynamic energy equation into the global corona model of the Space Weather Modeling Framework (SWMF), and its development into the new Lower Corona (LC) model. This work includes the integration of the additional energy transport terms of coronal heating, electron heat conduction, and optically thin radiative cooling into the governing magnetohydrodynamic (MHD) energy equation. We examine two different boundary conditions using this model; one set in the upper transition region (the Radiative Energy Balance model), as well as a uniform chro…
(abridged) AIMS. We investigate the dynamics and stability of post-shock plasma streaming along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. METHODS. We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model takes into account the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction. RESULTS. The structure, stability, and…
The presence of magnetic field is crucial in the transport of energy through the solar atmosphere. Recent ground-based and space-borne observations of the quiet Sun have revealed that magnetic field accumulates at photospheric heights, via a local dynamo or from small-scale flux emergence events. However, most of this small-scale magnetic field may not expand into the chromosphere due to the entropy drop with height at the photosphere. Here we present a study that uses a high resolution 3D radiative MHD simulation of the solar atmosphere with non-grey and non-LTE radiative transfer and thermal…
have forced the definition of a new type of spicule, "type II's", that are characterized by rising rapidly, having short lives, and by fading away at the end of their lifetimes. Here, we report on features found in realistic 3D simulations of the outer solar atmosphere that resemble the observed type II spicules. These features evolve naturally from the simulations as a consequence of the magnetohydrodynamical evolution of the model atmosphere. The simulations span from the upper layer of the convection zone to the lower corona and include the emergence of horizontal magnetic flux. The state-o…
The quantification of all possible waves and instabilities in a given system is of paramount importance, and knowledge of the full magnetohydrodynamic (MHD) spectrum allows one to predict the (in)stability of a given equilibrium state. This is highly relevant in many (astro)physical disciplines, and when applied to the solar atmosphere it may yield various new insights in processes like prominence formation and coronal loop oscillations. In this work we present a detailed, high-resolution spectroscopic study of the solar atmosphere, where we use our newly developed Legolas code to calculate th…
The heating of the solar chromosphere and corona to the observed high temperatures, imply the presence of ongoing heating that balances the strong radiative and thermal conduction losses expected in the solar atmosphere. It has been theorized for decades that the required heating mechanisms of the chromospheric and coronal parts of the active regions, quiet-Sun, and coronal holes are associated with the solar magnetic fields. However, the exact physical process that transport and dissipate the magnetic energy which ultimately leads to the solar plasma heating are not yet fully understood. The …
Surges are ubiquitous cool ejections in the solar atmosphere that often appear associated with transient phenomena like UV bursts or coronal jets. Recent observations from the Interface Region Imaging Spectrograph (IRIS) show that surges, although traditionally related to chromospheric lines, can exhibit enhanced emission in Si IV with brighter spectral profiles than for the average transition region (TR). In this paper, we explain why surges are natural sites to show enhanced emissivity in TR lines. We performed 2.5D radiative-MHD numerical experiments using the Bifrost code including the non…
We describe, analyze and validate the recently developed Alfvén Wave Solar Model (AWSoM), a 3D global model starting from the top of the chromosphere and extending into interplanetary space (up to 1-2 AU). This model solves the extended two temperature magnetohydrodynamics equations coupled to a wave kinetic equation for low frequency Alfvén waves. In this picture, heating and acceleration of the plasma are due to wave dissipation and wave pressure gradients, respectively. The dissipation process is described by a fully developed turbulent cascade of counter-propagating waves. We adopt a unifi…
The dynamical coupling between the solar chromospheric plasma and magnetic field is investigated by numerically solving a fully self-consistent, two-dimensional initial-value problem for the nonlinear collisional MHD equations including electric resistivity, thermal conduction, and, in some cases, gas-dynamic viscosity. The processes in the contact zone between two horizontal magnetic fields of opposite polarities are considered. The plasma is assumed to be initially motionless and having a temperature of 50,000 K uniform throughout the plasma volume; the characteristic magnetic field correspo…
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 dyna…
The solar chromosphere is weakly ionized and interactions between ionized particles and neutral particles likely have significant consequences for the thermodynamics of the plasma. We investigate the importance of introducing neutral particles using numerical 2.5D radiative MHD simulations obtained with the Bifrost code. The models span from the upper layers of the convection zone to the low corona, and solve the full MHD equations with non-grey and NLTE radiative transfer, and thermal conduction. The effects of partial ionization are implemented using the generalized Ohm's law. The approximat…
We investigate the thermal response of the atmosphere of a solar-type star to an electron beam injected from a hot Jupiter by performing a 1-dimensional magnetohydrodynamic numerical experiment with non-linear wave dissipation, radiative cooling, and thermal conduction. In our experiment, the stellar atmosphere is non-rotating and is modelled as a 1-D open flux tube expanding super-radially from the stellar photosphere to the planet. An electron beam is assumed to be generated from the reconnection site of the planet's magnetosphere. The effects of the electron beam are then implemented in our…
