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The object of this study is a regional center with a developed industry and a significant transport load. The study assesses the impact of car emissions on public health. It is shown that on average in the city, emissions from vehicles are 0.341mg/m∙s and vary from 0.038 to 1.012mg/m∙s. The main pollutants are nitrogen dioxide (from 39.3 to 58.5% of the total emission, the average value is 50.9%) and carbon monoxide (from 39.5 to 47.7%, the average value is 38.7%). There is an excess of the maximum permissible concentrations (MPC) by the content of NO2(1.5‒4.5MPC with an average value of 2.7MPC), formaldehyde (4.3‒4.4MPC ), hydrocarbons (1.2MPC), soot (1.3MPC). The level of carcinogenic danger for adults (R=1.9∙10-4) and children (R=3.8∙10-5‒9.8∙10-5) is rated as average. Soot (61.0%) and formaldehyde (38.9%) account for the largest contribution. Behind a non-carcinogenic risk, there is a significant danger of increasing morbidity of the population (HI=9.9‒14.0 with an average value of 11.1). Principal pollutants are formaldehyde (37%), NO2(23%), hydrocarbons (17%). The most vulnerable are the respiratory system (НІ=8.7) and the immune system (НІ=4.3). A significant health hazard is due to low fuel quality, technical and operational characteristics of cars, adverse natural conditions for the dispersion of impurities. The method of interpolation and extrapolation of the results of full-scale observations was used to assess the effect of gaseous and dust components from vehicles on humans. The current study makes it possible to assess the combined impact of pollutants on the risks of disease and premature death of the population, to identify the danger and zoning the territory by the level of danger. The results obtained can be important for making effective management decisions in the field of environmental protection and public health more...

The low efficiency of intellectual property (IP) in the public sector in our current economic environment is largely due to the insufficient development of the prevailing accounting and analytical system. Analytical methods, and the information basis of their application, are the core of this system. The formation of an accounting and analytical system consistent with the development priorities of public sector entities requires special research.This article provides a review of the methods and tools of analysis used by Russian and foreign scientists in the field of IP. Our research sample comprises 52 foreign and 39 Russian sources. Through a detailed textual analysis process, we systematise the existing methods used in the analyses of certain aspects of intellectual activity, and assess the information disclosure therein. Our evaluation is targeted towards identifying prospects for harmonising Russian and international approaches, and provide the groundwork for the improvement of accounting and analytical support for IP management in the public sector.Our results reveal possibilities for expanding the system of IP analysis methods for solving problems in the field of the IP economics and management on the basis of patent analytics. We also collate and classify patent analytics methods, and identify existing methodological problems at the macro- and microeconomic levels. Analytical methods are grouped inaccordance with three stages of the reciprocal model of IP accounting and analysis in the public sector, developed within the framework of a novel theoretical and methodological approach.In conclusion, we illustrate the potential for applying the methods of nonlinear dynamics and the dynamic theory of innovation (re: patent information) to determine the trajectories of public sector entity development concerning levels of information disclosure. We also identify areas for follow up research revealed through our analysis. more...

In this paper we present a numerical study of the dynamics of partially ionized coronal rain blobs. We use a two-fluid model to perform a high-resolution 2D simulation that takes into account the collisional interaction between the charged and neutral particles contained in the plasma. We follow the evolution of a cold plasma condensation as it falls through an isothermal vertically stratified atmosphere that represents the much hotter and lighter solar corona. We study the consequences of the different degrees of collisional coupling that are present in the system. On the one hand, we find that at the dense core of the blob there is a very strong coupling and the charged and neutral components of the plasma behave as a single fluid, with negligible drift velocities (of a few cm s^-1). On the other hand, at the edges of the blob the coupling is much weaker and larger drift velocities (of the order of 1 km s^-1) appear. In addition, frictional heating causes large increases of temperature at the transition layers between the blob and the corona. For the first time we show that such large drift velocities and temperature enhancements can develop as a consequence of ion-neutral decoupling associated to coronal rain dynamics. This can lead to enhanced emission coming from the plasma at the coronal rain-corona boundary, which possesses transition region temperature., Comment: 11 pages, 7 figures, and 1 animation. Accepted for publication in The Astrophysical Journal Letters more...

Large-amplitude longitudinal oscillations (LALOs) in solar prominences have been widely studied in the last decades. However, their damping and amplification mechanisms are not well understood. In this study, we investigate the attenuation and amplification of LALOs using high-resolution numerical simulations with progressively increasing spatial resolutions. We performed time-dependent numerical simulations of LALOs using the 2D magnetic configuration that contains a dipped region. After the prominence mass loading in the magnetic dips, we triggered LALOs by perturbing the prominence mass along the magnetic field. We performed the experiments with four values of spatial resolution. In the simulations with the highest resolution, the period shows a good agreement with the pendulum model. The convergence experiment revealed that the damping time saturates at the bottom prominence region with improving the resolution, indicating the existence of a physical reason for the damping of oscillations. At the prominence top, the oscillations are amplified during the first minutes and then are slowly attenuated. The characteristic time suggests more significant amplification in the experiments with the highest spatial resolution. The analysis revealed that the energy exchange between the bottom and top prominence regions is responsible for the attenuation and amplification of LALOs. The high-resolution experiments are crucial for the study of the periods and the damping mechanism of LALOs. The period agrees with the pendulum model only when using high enough spatial resolution. The results suggest that numerical diffusion in simulations with insufficient spatial resolution can hide important physical mechanisms, such as amplification of oscillations., 12 pages, 13 figures, accepted for publication in Astronomy and Astrophysics more...

Full list of authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei search; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming.-- This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/., The National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. © 2021, The Author(s)., This work rests on many years of sustained vision, effort, and dedication by DKIST and DKIST instrument, team scientists, engineers, and administrative, support personnel, the unwavering commitment of the National Science Foundation, and the support of the US taxpayers. It includes contributions from members of the DKIST Science Working Group and the DKIST Critical Science Plan Community, all of whom generously shared their experiences, plans, knowledge, and dreams. The research reported herein was based in part on the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST), a facility of the National Solar Observatory (NSO). NSO is managed by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the National Science Foundation., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709. more...

We analyzed multiline observations of a quiescent prominence from the slit spectrograph located at the Ondřejov Observatory. Dopplergrams and integrated intensity maps of the whole prominence were obtained from observations in six spectral lines: Ca ii H, Hϵ, Hβ, He i D3, Hα, and Ca ii IR. By combining integrated intensity maps with non-LTE radiative-transfer modeling, we carefully identified areas in an optically thin regime. The comparison of the Doppler-velocity maps and scatterplots from different lines shows the existence of differences in the velocity of ions and neutrals called velocity drift. The drift is of a local nature, present mostly at prominence edges in the area with a large velocity gradient, as can be tentatively expected based on multifluid MHD models. We could not explore the time evolution of the drift, since our data set consists of a single scan only. Our paper brings another contribution to a rather controversial problem of the detection of multifluid effects in solar prominences. more...

The importance of the chromosphere in the mass and energy transport within the solar atmosphere is now widely recognized. This review discusses the physics of magnetohydrodynamic waves and instabilities in large-scale chromospheric structures as well as in magnetic flux tubes. We highlight a number of key observational aspects that have helped our understanding of the role of the solar chromosphere in various dynamic processes and wave phenomena, and the heating scenario of the solar chromosphere is also discussed. The review focuses on the physics of waves and invokes the basics of plasma instabilities in the context of this important layer of the solar atmosphere. Potential implications, future trends and outstanding questions are also delineated. more...

In the absence of an initial seed, the Biermann battery term of a non-ideal induction equation acts as a source that generates weak magnetic fields. These fields are then amplified via a dynamo mechanism. The Kelvin-Helmholtz instability is a fluid phenomenon that takes place in many astrophysical scenarios and can trigger the action of the Biermann battery and dynamo processes. We aim to investigate the effect that the ionisation degree of the plasma and the interaction between the charged and neutral species have on the generation and amplification of magnetic fields during the different stages of the instability. We use the two-fluid model implemented in the numerical code Mancha-2F. We perform 2D simulations starting from a configuration with no initial magnetic field and which is unstable due to a velocity shear. We vary the ionisation degree of the plasma and we analyse the role that the different collisional terms included in the equations of the model play on the evolution of the instability and the generation of magnetic field. We find that when no collisional coupling is considered between the two fluids, the effect of the Biermann battery mechanism does not depend on the ionisation degree. However, when elastic collisions are taken into account, the generation of magnetic field is increased as the ionisation degree is reduced. This behaviour is slightly enhanced if the process of charge-exchange is also considered. We also find a dependence on the total density of the plasma related to the dependence on the coupling degree between the two fluids. As the total density is increased, the results from the two-fluid model converge to the predictions of single-fluid models., Comment: 20 pages, 13 figures, 2 movies. Accepted for publication in Astronomy & Astrophysics more...

Determining accurate plasma Doppler (line-of-sight) velocities from spectroscopic measurements is a challenging endeavour, especially when weak chromospheric absorption lines are often rapidly evolving and, hence, contain multiple spectral components in their constituent line profiles. Here, we present a novel method that employs machine learning techniques to identify the underlying components present within observed spectral lines, before subsequently constraining the constituent profiles through single or multiple Voigt fits. Our method allows active and quiescent components present in spectra to be identified and isolated for subsequent study. Lastly, we employ a Ca II 8542 {\AA} spectral imaging dataset as a proof-of-concept study to benchmark the suitability of our code for extracting two-component atmospheric profiles that are commonly present in sunspot chromospheres. Minimisation tests are employed to validate the reliability of the results, achieving median reduced $\chi^2$ values equal to 1.03 between the observed and synthesised umbral line profiles., Comment: 23 pages, 8 figures. Improved formatting of abstract and references more...

Multi-fluid magnetohydrodynamics is an extension of classical magnetohydrodynamics that allows a simplified treatment plasmas with complex chemical mixtures. The types of plasma susceptible to multi-fluid effects are those containing particles with properties significantly different from those of the rest of the plasma in either mass, or electric charge, such as neutral particles, molecules, or dust grains. In astrophysics, multi-fluid magnetohydrodynamics is relevant for planetary ionospheres and magnetospheres, the interstellar medium, and the formation of stars and planets, as well as in the atmospheres of cool stars such as the Sun. Traditionally, magnetohydrodynamics has been a classical approximation in many astrophysical and physical applications. Magnetohydrodynamics works well in dense plasmas where the typical plasma scales (e.g., cyclotron frequencies, Larmor radius) are significantly smaller than the scales of the processes under study. Nevertheless, when plasma components are not well coupled by collisions it is necessary to replace single-fluid magnetohydrodynamics by multi-fluid theory. The present article provides a description of environments in which a multi-fluid treatment is necessary and describes modifications to the magnetohydrodynamic equations that are necessary to treat non-ideal plasmas. It also summarizes the physical consequences of major multi-fluid non-ideal magnetohydrodynamic effects including ambipolar diffusion, the Hall effect, the battery effect, and other intrinsically multi-fluid effects. Multi-fluid theory is an intermediate step between magnetohydrodynamics dealing with the collective behaviour of an ensemble of particles, and a kinetic approach where the statistics of particle distributions are studied. The main assumption of multi-fluid theory is that each individual ensemble of particles behaves like a fluid, interacting via collisions with other particle ensembles, such as those belonging to different chemical species or ionization states. Collisional interaction creates a relative macroscopic motion between different plasma components, which, on larger scales, results in the non-ideal behaviour of such plasmas. The non-ideal effects discussed here manifest themselves in plasmas at relatively low temperatures and low densities. more...

Prominence threads are very long and thin flux tubes which are partially filled with cold plasma. Observations have shown that transverse oscillations are frequent in these solar structures. The observations are usually interpreted as the fundamental kink mode, while the detection of the first harmonic remains elusive. Here, we aim to study how the density inhomogeneity in the longitudinal and radial directions modify the periods and damping times of kink oscillations, and how this effect would be reflected in observations. We solve the ideal magnetohydrodynamics equations through two different methods: a) performing 3D numerical simulations, and b) solving a 2D generalised eigenvalue problem. We study the dependence of the periods, damping times and amplitudes of transverse kink oscillations on the ratio between the densities at the centre and at the ends of the tube, and on the average density. We apply forward modelling on our 3D simulations to compute synthetic H$\alpha$ profiles. We confirm that the ratio of the period of the fundamental oscillation mode to the period of the first harmonic increases as the ratio of the central density to the footpoint density is increased or as the averaged density of the tube is decreased. We find that the damping times due to resonant absorption decrease as the central to footpoint density ratio increases. Contrary to the case of longitudinally homogeneous tubes, we find that the damping time to period ratio also increases as the density ratio is increased or the average density is reduced. We present snapshots and time-distance diagrams of the emission in the H$\alpha$ line. The results presented here have implications for the field of prominence seismology. While the H$\alpha$ emission can be used to detect the fundamental mode, the first harmonic is barely detectable in H$\alpha$. This may explain the lack of detections of the first harmonic., Comment: 17 pages, 16 figures, 4 movies. Accepted for publication in Astronomy & Astrophysics more...

The conducted analysis of the prospects of international environmental cooperation for the central regions of Ukraine showed that the most developed area of cooperation is green tourism, which is rapidly developing in the central regions. To a large extent, this is due to the natural conditions and the preserved archaism of local life that attracts tourists. On the other side, the support of green tourism by the government, improvement of the material condition of owners of green homesteads increases the interest of local communities in cooperation with international organizations. Using of international experience in the field of energy saving by local communities is being implemented by individual farms at the level of individual relationships with international organizations, but it has no massive component. Cooperation of the central regions of Ukraine with the international community is the most promising in the direction of forming a transnational ecological network. The main reserve for the formation of a regional ecological network is the lands of the water fund, degraded and unproductive agricultural landscapes. The allocation of lands for the water fund and its mapping must use plans and requires adequate financing. The threat to implementation of the regional program for the development of the ecological network and its coordination with transnational ecological corridors is the lack of financing and inconsistency of the resolution of the land ownership rights in the alienation of land to the nature reserve fund. The use of funding from international environmental funds in the central regions of Ukraine is limited due to the lack of experience in the participation of environmental NGOs in international ecological projects aimed at nature conservation, the lack of interest of local communities in land alienation in the nature reserve fund. more...

This paper presents the results of the analysis of three-dimensional simulations of solar magneto-convection that include the joint action of the ambipolar diffusion and the Hall effect. Three simulation runs are compared: one including both ambipolar diffusion and the Hall effect; one including only ambipolar diffusion and one without any of these two effects. The magnetic field is amplified from initial field to saturation level by the action of turbulent local dynamo. In each of these cases, we study 2 h of simulated solar time after the local dynamo reaches the saturation regime. We analyse the power spectra of vorticity, of magnetic field fluctuations and of the different components of the magnetic Poynting flux responsible for the transport of vertical or horizontal perturbations. Our preliminary results show that the ambipolar diffusion produces a strong reduction of vorticity in the upper chromospheric layers and that it dissipates the vortical perturbations converting them into thermal energy. The Hall effect acts in the opposite way, strongly enhancing the vorticity. When the Hall effect is included, the magnetic field in the simulations becomes, on average, more vertical and long-lived flux tube-like structures are produced. We trace a single magnetic structure to study its evolution pattern and the magnetic field intensification, and their possible relation to the Hall effect. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’. more...

Solar prominences are formed by partially ionized plasma with inter-particle collision frequencies, which generally warrant magnetohydrodynamic treatment. In this work, we explore the dynamical impacts and observable signatures of two-fluid effects in the parameter regimes when ion-neutral collisions do not fully couple the neutral and charged fluids. We performed 2.5D two-fluid (charge – neutrals) simulations of the Rayleigh-Taylor instability (RTI) at a smoothly changing interface between a solar prominence thread and the corona. The purpose of this study is to deepen our understanding of the RTI and the effects of partial ionization on the development of the RTI using nonlinear two-fluid numerical simulations. Our two-fluid model takes into account viscosity, thermal conductivity, and collisional interaction between neutrals and charge: ionization or recombination, energy and momentum transfer, and frictional heating. In this paper, we explore the sensitivity of the RTI dynamics to the prominence equilibrium configuration, including the impact of the magnetic field strength and shear supporting the prominence thread, and the amount of prominence mass-loading. We show that at small scales, a realistically smooth prominence-corona interface leads to qualitatively different linear RTI evolution than that which is expected for a discontinuous interface, while magnetic field shear has the stabilizing effect of reducing the growth rate or eliminating the instability. In the nonlinear phase, we observe that in the presence of field shear the development of the instability leads to formation of coherent and interacting 2.5D magnetic structures, which, in turn, can lead to substantial plasma flow across magnetic field lines and associated decoupling of the fluid velocities of charged particles and neutrals. more...

This chapter provides a brief overview on how the inclusion of extra physics in standard magnetohydrodynamics affects waves and instabilities. The inclusion of such extra physics is important for many plasma systems, such as planetary ionospheres and magnetospheres, the interstellar medium and molecular clouds and also the atmospheres of cool stars such as the Sun. more...

Solar chromosphere consists of a partially ionized plasma, which makes modeling the solar chromosphere a particularly challenging numerical task. Here we numerically model chromospheric waves using a two-fluid approach with a newly developed numerical code. The code solves two-fluid equations of conservation of mass, momentum, and energy, together with the induction equation for the case of the purely hydrogen plasma with collisional coupling between the charged and neutral fluid components. The implementation of a semi-implicit algorithm allows us to overcome the numerical stability constraints due to the stiff collisional terms. We test the code against analytical solutions of acoustic and Alfvén wave propagation in uniform medium in several regimes of collisional coupling. The results of our simulations are consistent with the analytical estimates, and with other results described in the literature. In the limit of a large collisional frequency, the waves propagate with a common speed of a single fluid. In the other limit of a vanishingly small collisional frequency, the Alfvén waves propagate with an Alfvén speed of the charged fluid only, while the perturbation in neutral fluid is very small. The acoustic waves in these limits propagate with the sound speed corresponding to either the charges or the neutrals, while the perturbation in the other fluid component is negligible. Otherwise, when the collision frequency is similar to the real part of the wave frequency, the interaction between charges and neutrals through momentum-transfer collisions cause alterations of the waves frequencies and damping of the wave amplitudes. more...

Solar prominences are formed by partially ionized plasma with inter-particle collision frequencies generally warranting magnetohydrodynamic treatment. In this work we explore the dynamical impacts and observable signatures of two-fluid effects in the parameter regimes when ion-neutral collisions do not fully couple the neutral and charged fluids. We perform 2.5D two-fluid (charges-neutrals) simulations of the Rayleigh-Taylor instability (RTI) at a smoothly changing interface between a solar prominence thread and the corona. The purpose of this study is to deepen our understanding of the RTI and the effects of the partial ionization on the development of RTI using nonlinear two-fluid numerical simulations. Our two-fluid model takes into account neutral viscosity, thermal conductivity, and collisional interaction between neutrals and charges: ionization–recombination, energy and momentum transfer, and frictional heating. In this paper, the sensitivity of the RTI dynamics to collisional effects for different magnetic field configurations supporting the prominence thread is explored. This is done by artificially varying, or eliminating, effects of both elastic and inelastic collisions by modifying the model equations. We find that ionization and recombination reactions between ionized and neutral fluids do not substantially impact the development of the primary RTI. However, such reactions can impact the development of secondary structures during the mixing of the cold prominence and hotter surrounding coronal material. We find that collisionality within and between ionized and neutral particle populations plays an important role in both linear and nonlinear development of RTI; ion-neutral collision frequency is the primary determining factor in development or damping of small-scale structures. We also observe that the degree and signatures of flow decoupling between ion and neutral fluids can depend on the inter-particle collisionality and on the magnetic field configuration of the prominence thread. more...

The partial ionization of the solar plasma causes several nonideal effects such as the ambipolar diffusion, the Hall effect, and the Biermann battery effect. Here we report on the first three-dimensional realistic simulations of solar local dynamo where all three effects were taken into account. The simulations started with a snapshot of already saturated battery-seeded dynamo, where two new series were developed: one with solely ambipolar diffusion and another one also taking into account the Hall term in the generalized Ohm's law. The simulations were then run for about 4 hours of solar time to reach the stationary regime and improve the statistics. In parallel, a purely MHD dynamo simulation was also run for the same amount of time. The simulations are compared in a statistical way. The results show that, with the inclusion of the ambipolar diffusion, the amplitudes of the incompressible perturbations related to Alfven waves are reduced, and the Poynting flux is absorbed, with a frequency dependence. The Hall effect causes the opposite action: significant excess of incompressible perturbations is generated and an excess of the Poynting flux is observed in the chromospheric layers. The model with ambipolar diffusion shows, on average, sharper current sheets and slightly more abundant fast magneto-acoustic shocks in the chromosphere. The model with the Hall effect has higher temperatures at the lower chromosphere and stronger and more vertical magnetic field concentrations all over the chromosphere. The study of high-frequency waves reveals that significant power of incompressible perturbations is associated with areas with intense and more vertical magnetic fields and larger temperatures. We find a positive correlation between the magnitude of the ambipolar heating and the temperature increase at the same location after a characteristic time of 10^2 sec., To appear in Astronomy & Astrophysics more...

Context. Large-amplitude oscillations (LAOs) of the solar prominences are very spectacular but poorly understood phenomena. These motions have amplitudes larger than $10 {\mathrm{\, km \,s^{-1}}}$ and can be triggered by the external perturbations, e.g., Moreton or EIT waves. Aims. Our aim is to analyze the properties of large-amplitude oscillations using realistic prominence models and the triggering mechanism by external disturbances. Methods. We perform time-dependent numerical simulations of LAOs using a magnetic flux rope model with two values of the shear angle and the density contrast. We study the internal modes of the prominence using the horizontal and vertical triggering. In addition, we use the perturbation that arrives from outside in order to understand how such external disturbance can produce LAOs. Results. The period of longitudinal oscillations and its behavior with height show good agreement with the pendulum model. The period of transverse oscillations remains constant with height, suggesting a global normal mode. The transverse oscillations typically have shorter periods than the longitudinal oscillations. Conclusions. The periods of the longitudinal and transverse oscillations show only weak dependence on the shear angle of the magnetic structure and the prominence density contrast. The external disturbance perturbs the flux rope exciting oscillations of both polarizations. Their properties are a mixture of those excited by purely horizontal and vertical driving., Comment: 15 pages, 10 figures, accepted for publication in Astronomy and Astrophysics more...

In Part 2 of our guide to collisionless fluid models, we concentrate on Landau fluid closures. These closures were pioneered by Hammett and Perkins and allow for the rigorous incorporation of collisionless Landau damping into a fluid framework. It is Landau damping that sharply separates traditional fluid models and collisionless kinetic theory, and is the main reason why the usual fluid models do not converge to the kinetic description, even in the long-wavelength low-frequency limit. We start with a brief introduction to kinetic theory, where we discuss in detail the plasma dispersion function $Z(\zeta)$, and the associated plasma response function $R(\zeta)=1+\zeta Z(\zeta)=-Z'(\zeta)/2$. We then consider a 1D (electrostatic) geometry and make a significant effort to map all possible Landau fluid closures that can be constructed at the 4th-order moment level. These closures for parallel moments have general validity from the largest astrophysical scales down to the Debye length, and we verify their validity by considering examples of the (proton and electron) Landau damping of the ion-acoustic mode, and the electron Landau damping of the Langmuir mode. We proceed by considering 1D closures at higher-order moments than the 4th-order, and as was concluded in Part 1, this is not possible without Landau fluid closures. We show that it is possible to reproduce linear Landau damping in the fluid framework to any desired precision, thus showing the convergence of the fluid and collisionless kinetic descriptions. We then consider a 3D (electromagnetic) geometry in the gyrotropic (long-wavelength low-frequency) limit and map all closures that are available at the 4th-order moment level. In the Appendix A, we provide comprehensive tables with Pad\'e approximants of $R(\zeta)$ up to the 8th-pole order, with many given in an analytic form., Comment: Improved version, now accepted to JPP Lecture Notes. Some parts were shortened and some parts were expanded. The text now contains Conclusions more...

The interaction of plasma with magnetic field in the partially ionised solar atmosphere is frequently modelled via a single-fluid approximation, which is valid for the case of a strongly coupled collisional media, such as solar photosphere and low chromosphere. Under the single-fluid formalism the main non-ideal effects are described by a series of extra terms in the generalised induction equation and in the energy conservation equation. These effects are: Ohmic diffusion, ambipolar diffusion, the Hall effect, and the Biermann battery effect. From the point of view of the numerical solution of the single-fluid equations, when ambipolar diffusion or Hall effects dominate can introduce severe restrictions on the integration time step and can compromise the stability of the numerical scheme. In this paper we introduce two numerical schemes to overcome those limitations. The first of them is known as super time-stepping (STS) and it is designed to overcome the limitations imposed when the ambipolar diffusion term is dominant. The second scheme is called the Hall diffusion scheme (HDS) and it is used when the Hall term becomes dominant. These two numerical techniques can be used together by applying Strang operator splitting. This paper describes the implementation of the STS and HDS schemes in the single-fluid codeMANCHA3D. The validation for each of these schemes is provided by comparing the analytical solution with the numerical one for a suite of numerical tests. more...

Solar active regions show a wide variety of oscillatory phenomena. The presence of the magnetic field leads to the appearance of several wave modes, whose behavior is determined by the sunspot thermal and magnetic structure. We aim to study the relation between the umbral and penumbral waves observed at the high photosphere and the magnetic field topology of the sunspot. Observations of the sunspot in active region NOAA 12662 obtained with the GREGOR telescope (Observatorio del Teide, Spain) were acquired on 2017 June 17. The data set includes a temporal series in the Fe I 5435 \AA\ line obtained with the imaging spectrograph GREGOR Fabry-P\'erot Interferometer (GFPI) and a spectropolarimetric raster map acquired with the GREGOR Infrared Spectrograph (GRIS) in the 10830 \AA\ spectral region. The Doppler velocity deduced from the restored Fe I 5435 \AA\ line has been determined, and the magnetic field vector of the sunspot has been inferred from spectropolarimetric inversions of the Ca I 10839 \AA\ and the Si I 10827 \AA\ lines. A two-armed spiral wavefront has been identified in the evolution of the two-dimensional velocity maps from the Fe I 5435 \AA\ line. The wavefronts initially move counterclockwise in the interior of the umbra, and develop into radially outward propagating running penumbral waves when they reach the umbra-penumbra boundary. The horizontal propagation of the wavefronts approximately follows the direction of the magnetic field, which shows changes in the magnetic twist with height and horizontal position. The spiral wavefronts are interpreted as the visual pattern of slow magnetoacoustic waves which propagate upward along magnetic field lines. Their apparent horizontal propagation is due to their sequential arrival to different horizontal positions at the formation height of the Fe I 5435 \AA\ line, as given by the inclination and orientation of the magnetic field., Comment: Accepted for publication in A&A more...

Context. Coronal rain often comes about as the final product of evaporation and condensation cycles that occur in active regions. Observations show that the condensed plasma falls with an acceleration that is less than that of free fall. Aims. We aim to improve the understanding of the physical mechanisms behind the slower than free-fall motion and the two-stage evolution (an initial phase of acceleration followed by an almost constant velocity phase) detected in coronal rain events. Methods. Using the MANCHA3D code, we solve the 2D ideal magnetohydrodynamic equations. We represent the solar corona as an isothermal vertically stratified atmosphere with a uniform vertical magnetic field. We represent the plasma condensation as a density enhancement described by a 2D Gaussian profile. We analyse the temporal evolution of the descending plasma and study its dependence on such parameters as density and magnetic field strength. Results. We confirm previous findings that indicate that the pressure gradient is the main force that opposes the action of gravity and slows down the blob descent, and that larger densities require larger pressure gradients to reach the constant speed phase. We find that the shape of a condensation with a horizontal variation of density is distorted during its fall because the denser parts of the blob fall faster than the lighter ones. This is explained by the fact that the duration of the initial acceleration phase and, therefore, the maximum falling speed attained by the plasma, increases with the ratio of blob to coronal density. We also find that the magnetic field plays a fundamental role in the evolution of the descending condensations. A strong enough magnetic field (greater than 10 G in our simulations) forces each plasma element to follow the path given by a particular field line, which allows for the description of the evolution of each vertical slice of the blob in terms of 1D dynamics, without the influence of the adjacent slices. In addition, under the typical conditions of the coronal rain events, the magnetic field prevents the development of Kelvin-Helmholtz instability. more...

Waves and shocks traveling through the solar chromospheric plasma are influenced by its partial ionization and weak collisional coupling, and may become susceptible to multi-fluid effects, similar to interstellar shock waves. In this study, we consider fast magneto-acoustic shock wave formation and propagation in a stratified medium, that is permeated by a horizontal magnetic field, with properties similar to that of the solar chromosphere. The evolution of plasma and neutrals is modeled using a two-fluid code that evolves a set of coupled equations for two separate fluids. We observed that waves in neutrals and plasma, initially coupled at the upper photosphere, become uncoupled at higher heights in the chromosphere. This decoupling can be a consequence of either the characteristic spatial scale at the shock front, that becomes similar to the collisional scale, or the change in the relation between the wave frequency, ion cyclotron frequency, and the collisional frequency with height. The decoupling height is a sensitive function of the wave frequency, wave amplitude, and the magnetic field strength. We observed that decoupling causes damping of waves and an increase in the background temperature due to the frictional heating. The comparison between analytical and numerical results allows us to separate the role of the nonlinear effects from the linear ones on the decoupling and damping of waves. more...

Photospheric waves in sunspots moving radially outwards at speeds faster than the characteristic wave velocities have been recently detected. It has been suggested that they are the visual pattern of $p-$modes excited around 5 Mm beneath the sunspot. Using numerical simulations, we have performed a parametric study of the waves observed at the photosphere and higher layers produced by sources located at different depths. The observational measurements are consistent with waves driven between approximately 1 Mm and 5 Mm below the sunspot surface., Accepted for publication in A&A more...

This work aims to understand the behavior of non-linear waves in the vicinity of a coronal null point. In previous works we have showed that high frequency waves are generated in such magnetic configuration. This paper studies those waves in detail in order to provide a plausible explanation of their generation. We demonstrate that slow magneto-acoustic shock waves generated in the chromosphere propagate through the null point and produce a train of secondary shocks that escape along the field lines. A particular combination of the shock wave speeds generates waves at a frequency of 80 mHz. We speculate that this frequency may be sensitive to the atmospheric parameters in the corona and therefore can be used to probe the structure of this solar layer. more...

Partially ionized plasmas are found across the Universe in many different astrophysical environments. They constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environments, and display a richness of physical effects which are not present in fully ionized plasmas. This review provides an overview of the physics of partially ionized plasmas, including recent advances in different astrophysical areas in which partial ionization plays a fundamental role. We outline outstanding observational and theoretical questions and discuss possible directions for future progress., Comment: 163 pages, submitted to Space Science Reviews more...

The magnetic fields of the quiet Sun cover at any time more than 90\% of its surface and their magnetic energy budget is crucial to explain the thermal structure of the solar atmosphere. One of the possible origins of these fields is due to the action of local dynamo in the upper convection zone of the Sun. Existing simulations of the local solar dynamo require an initial seed field, and sufficiently high spatial resolution, in order to achieve the amplification of the seed field to the observed values in the quiet Sun. Here we report an alternative model of seeding based on the action of the Bierman battery effect. This effect generates a magnetic field due to the local imbalances in electron pressure in the partially ionized solar plasma. We show that the battery effect self-consistently creates from zero an initial seed field of a strength of the order of micro G, and together with dynamo amplification, allows the generation of quiet Sun magnetic fields of a similar strength to those from solar observations., Comment: To appear in Astronomy & Astrophysics more...

We present results of the study of chromospheric and photospheric line-of-sight velocity fields in the young active region NOAA 11024. Multi-layer, multi-wavelength observational data were used for the analysis of the emerging flux in this active region. Spectropolarimetric observations were carried out with the telescope THEMIS on Tenerife (Canary Islands) on 4 July 2009. In addition, space-borne data from SOHO/MDI, STEREO and GOES were also considered. The combination of data from ground- and space-based telescopes allowed us to study the dynamics of the lower atmosphere of the active region with high spatial, spectral, and temporal resolutions. THEMIS spectra show strong temporal variations of the velocity in the chromosphere and photosphere for different activity features: two pores, active and quiet plage regions, and two surges. The range of variations of the chromospheric line-of-sight velocity at the heights of formation of the H-alpha core was extremely large. Both upward and downward motions were observed in these layers. In particular, a surge with upward velocities up to -73 km/s were detected. In the photosphere, predominantly upward motions were found, varying from -3.1 km/s upflows to 1.4 km/s downflows in different structures. The velocity variations at different levels in the lower atmosphere are compatible with magnetic flux emergence., 17 pages, 8 figures; accepted for publication in Solar Physics more...

We report a detection of differences in ion and neutral velocities in prominences using high resolution spectral data obtained in September 2012 at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife). A time series of scans of a small portion of a solar prominence was obtained simultaneously with a high cadence using the lines of two elements with different ionization states, namely the CaII 8542 A and the HeI 10830 A. Displacements, widths and amplitudes of both lines were carefully compared to extract dynamical information about the plasma. Many dynamical features are detected, such as counterstreaming flows, jets and propagating waves. In all the cases we find very strong correlation between the parameters extracted from the lines of both elements, confirming that both trace the same plasma. Nevertheless, we also find short-lived transients where this correlation is lost. These transients are associated with the ion-neutral drift velocities of the order of several hundred m/s. The patches of non-zero drift velocity show coherence on time-distance diagrams., To appear in The Astrophysical Journal more...

Coupling between fast magneto-acoustic and Alfv\'en waves can be observe in fully ionized plasmas mediated by stratification and 3D geometrical effects. In Paper I, Cally & Khomenko (2015) have shown that in a weakly ionized plasma, such as the solar photosphere and chromosphere, the Hall current introduces a new coupling mechanism. The present study extends the results from Paper I to the case of warm plasma. We report on numerical experiments where mode transformation is studied using quasi-realistic stratification in thermodynamic parameters resembling the solar atmosphere. This redresses the limitation of the cold plasma approximation assumed in Paper I, in particular allowing the complete process of coupling between fast and slow magneto-acoustic modes and subsequent coupling of the fast mode to the Alfv\'en mode through the Hall current. Our results confirm the efficacy of the mechanism proposed in Paper I for the solar case. We observe that the efficiency of the transformation is a sensitive function of the angle between the wave propagation direction and the magnetic field, and of the wave frequency. The efficiency increases when the field direction and the wave direction are aligned for increasing wave frequencies. After scaling our results to typical solar values, the maximum amplitude of the transformed Alfv\'en waves, for a frequency of 1 Hz, corresponds to an energy flux (measured above the height of peak Hall coupling) of $\sim10^3$ $\rm W\,m^{-2}$, based on an amplitude of 500 $\rm m\,s^{-1}$ at $\beta=1$, which is sufficient to play a major role in both quiet and active region coronal heating. more...

The Sunrise balloon-borne solar observatory consists of a 1m aperture Gregory telescope, a UV filter imager, an imaging vector polarimeter, an image stabilization system and further infrastructure. The first science flight of Sunrise yielded high-quality data that reveal the structure, dynamics and evolution of solar convection, oscillations and magnetic fields at a resolution of around 100 km in the quiet Sun. Here we describe very briefly the mission and the first results obtained from the Sunrise data, which include a number of discoveries. more...

Waves observed in the photosphere and chromosphere of sunspots show complex dynamics and spatial patterns. The interpretation of high-resolution sunspot wave observations requires modeling of three-dimensional (3D) nonlinear wave propagation and mode transformation in the sunspot upper layers in realistic spot model atmospheres. Here, we present the first results of such modeling. We have developed a 3D nonlinear numerical code specially designed to calculate the response of magnetic structures in equilibrium to an arbitrary perturbation. The code solves the 3D nonlinear MHD equations for perturbations; it is stabilized by hyper-diffusivity terms and is fully parallelized. The robustness of the code is demonstrated by a number of standard tests. We analyze several simulations of a sunspot perturbed by pulses of different periods at a subphotospheric level, from short periods, introduced for academic purposes, to longer and realistic periods of 3 and 5 minutes. We present a detailed description of the 3D mode transformation in a non-trivial sunspot-like magnetic field configuration, including the conversion between fast and slow magneto-acoustic waves and the Alfven wave, by calculation of the wave energy fluxes. Our main findings are as follows: (1) the conversion from acoustic to the Alfven mode is only observed if the driving pulse is located out of the sunspot axis, but this conversion is energetically inefficient; (2) as a consequence of the cutoff effects and refraction of the fast magneto-acoustic mode, the energy of the evanescent waves with periods around 5 minutes remains almost completely below the level β = 1; (3) waves with frequencies above the cutoff propagate field aligned to the chromosphere and their power becomes dominating over that of evanescent 5 minute oscillations, in agreement with observations. more...

We suggest an explanation for the high-frequency power excess surrounding active regions known as seismic halos. The idea is based on numerical simulations of magneto-acoustic waves propagation in sunspots. We propose that such an excess can be caused by the additional energy injected by fast mode waves refracted in the higher atmosphere due to the rapid increase of the Alfven speed. Our model qualitatively explains the magnitude of the halo and allows to make some predictions of its behavior that can be checked in future observations., Comment: Accepted by Astronomy and Astrophysics Letters more...

Context. The energy source powering the solar chromosphere is still undetermined, but leaves its traces in observed intensities. Aims. We investigate the statistics of the intensity distributions as a function of the wavelength for Caii Ha nd the Caii IR line at 854.2 nm to estimate the energy content in the observed intensity fluctuations. Methods. We derived the intensity variations at different heights of the solar atmosphere, as traced by the line wings and line cores of the two spectral lines. We converted the observed intensities to absolute energy units employing reference profiles calculated in non-local thermal equilibrium (NLTE). We also converted the intensity fluctuations to corresponding brightness temperatures assuming LTE. Results. The root-mean-square (rms) fluctuations of the emitted intensity are about 0.6 (1.2) W m −2 ster −1 pm −1 near the core of the Caii IR line at 854.2 nm (Caii H), corresponding to relative intensity fluctuations of about 20% (30%). For the line wing, we find rms values of about 0.3 W m −2 ster −1 pm −1 for both lines, corresponding to relative fluctuations below 5%. The relative rms values show a local minimum for wavelengths forming at a height of about 130 km, but otherwise increase smoothly from the wing to the core, i.e., from photosphere to chromosphere. The corresponding rms brightness temperature fluctuations are below 100 K for the photosphere and up to 500 K in the chromosphere. The skewness of the intensity distributions is close to zero in the outer line wing and positive throughout the rest of the line spectrum, owing to the frequent occurrence of high-intensity events. The skewness shows a pronounced local maximum at locations with photospheric magnetic fields for wavelengths in-between those of the line wing and the line core (z ≈ 150−300 km), and a global maximum at the very core (z ≈ 1000 km) for both magnetic and field-free locations. Conclusions. The energy content of the intensity fluctuations is insufficient to create a chromospheric temperature rise that would be similar to the one in most reference models of the solar atmosphere. The increase in the rms fluctuations with height indicates the presence of upwardly propagating acoustic waves of increasing oscillation amplitude. The intensity and temperature variations indicate that there is a clear increase in dynamical activity from photosphere towards the chromosphere, but the variations fall short of the magnitude predicted by fully dynamical chromospheric models by a factor of about five. The enhanced skewness between the photosphere and lower solar chromosphere at magnetic locations is indicative of a mechanism that acts solely on magnetized plasma. more...

Instituto de Astrof´isica de Canarias, 38205, C/ V´ia L´actea, s/n, Tenerife, Spain e-mail: khomenko@iac.esReceived date; accepted dateABSTRACTAims. The aim of this paper is to analyse the validity of the Dopplergram and λ-meter techniques for the Dopplerdiagnostics of solar photospheric velocities using the Baii 4554 ˚A line.Methods. Both techniques are evaluated by means of NLTE radiative transfer calculations of the Baii 4554 ˚A line ina three-dimensional hydrodynamical model of solar convection. We consider the cases of spatially unsmeared profilesand the profiles smeared to the resolution of ground-based observations.Results. We find that: (i) Speckle-reconstructed Dopplergram velocities reproduce the “true” velocities well at heightsaround 300 km, except for intergranular lanes with strong downflows where the velocity can be overestimated. (ii)The λ-meter velocities give a good representation of the “true” velocities through the whole photosphere, both underthe original and reduced spatial resolutions. The velocities derived from the inner wing of smeared Baii 4554 ˚A lineprofiles are more reliable than those for the outer wing. Only under high spatial resolution does the inner wing velocitiescalculated in intergranular regions give an underestimate (or even a sign reversal) compared with the model velocities.(iii) NLTE effects should be taken into account in modelling the Baii 4554 ˚A line profiles. Such effects are morepronounced in intergranular regions.Conclusions. Our analysis supports the opinion that the Dopplergram technique applied to the Baii 4554 ˚A line is avaluable tool for the Doppler diagnostics of the middle photosphere around 300 km. The λ-meter technique appliedto this line gives us a good opportunity to “trace” the non-thermal motions along the whole photosphere up to thetemperature minimum and lower chromosphere.Key words.Sun – photosphere: Sun – granulation: line – formation: techniques – spectroscopic – hydrodynamics – radiative transfer more...

We report two-dimensional MHD simulations which demonstrate that photospheric 5-min oscillations can leak into the chromosphere inside small-scale vertical magnetic flux tubes. The results of our numerical experiments are compatible with those inferred from simultaneous spectropolarimetric observations of the photosphere and chromosphere obtained with the Tenerife Infrared Polarimeter (TIP) at 10830 A. We conclude that the efficiency of energy exchange by radiation in the solar photosphere can lead to a significant reduction of the cut-off frequency and may allow for the propagation of the 5 minutes waves vertically into the chromosphere., accepted by ApJL more...

The reliability of quiet-Sun magnetic field diagnostics based on the Fe I lines at 6302 A has been questioned by recent work. Here we present the results of a thorough study of high-resolution multiline observations taken with the new spectropolarimeter SPINOR, comprising the 5250 and 6302 A spectral domains. The observations were analyzed using several inversion algorithms, including Milne-Eddington, LTE with 1 and 2 components, and MISMA codes. We find that the line-ratio technique applied to the 5250 A lines is not sufficiently reliable to provide a direct magnetic diagnostic in the presence of thermal fluctuations and variable line broadening. In general, one needs to resort to inversion algorithms, ideally with realistic magnetohydrodynamic constrains. When this is done, the 5250 A lines do not seem to provide any significant advantage over those at 6302 A. In fact, our results point toward a better performance with the latter (in the presence of turbulent line broadening). In any case, for very weak flux concentrations, neither spectral region alone provides sufficient constraints to fully disentangle the intrinsic field strengths. Instead, we advocate for a combined analysis of both spectral ranges, which yields a better determination of the quiet-Sun magnetic properties. Finally, we propose the use of two other Fe I lines (at 4122 and 9000 A) with identical line opacities that seem to work much better than the others. more...

In this paper, we show a "proof of concept" of the heating mechanism of the solar chromosphere due to wave dissipation caused by the effects of partial ionization. Numerical modeling of non-linear wave propagation in a magnetic flux tube, embedded in the solar atmosphere, is performed by solving a system of single-fluid quasi-MHD equations, which take into account the ambipolar term from the generalized Ohm's law. It is shown that perturbations caused by magnetic waves can be effectively dissipated due to ambipolar diffusion. The energy input by this mechanism is continuous and shown to be more efficient than dissipation of static currents, ultimately leading to chromospheric temperature increase in magnetic structures., Comment: 7 pages, 5 figures more...

International audience; Context. Waves in the magnetized solar atmosphere are one of the favourite means of transferring and depositing energy into the solar corona. The study of waves brings information not just on the dynamics of the magnetized plasma, but also on the possible ways in which the corona is heated. Aims: The identification and analysis of the phase singularities or dislocations provide us with a complementary approach to the magnetoacoustic and Aflvén waves propagating in the solar atmosphere. They allow us to identify individual wave modes, shedding light on the probability of excitation or the nature of the triggering mechanism. Methods: We use a time series of Doppler shifts measured in two spectral lines, filtered around the three-minute period region. The data show a propagating magnetoacoustic slow mode with several dislocations and, in particular, a vortex line. We study under what conditions the different wave modes propagating in the umbra can generate the observed dislocations. Results: The observed dislocations can be fully interpreted as a sequence of sausage and kink modes excited sequentially on average during 15 min. Kink and sausage modes appear to be excited independently and sequentially. The transition from one to the other lasts less than three minutes. During the transition we observe and model the appearance of superoscillations inducing large phase gradients and phase mixing. Conclusions: The analysis of the observed wave dislocations leads us to the identification of the propagating wave modes in umbrae. The identification in the data of superoscillatory regions during the transition from one mode to the other may be an important indicator of the location of wave dissipation. more...

Aims. The aim of this paper is to analyze the thermal properties, oscillatory, and flow motions of a bright, long-lasting feature observed in solar granulation, which we call the plume. Methods. We used the spectral observations of quiet granulation at solar disc center, including the two Fe ii 5234 and Fe i 6393 A lines recorded simultaneously at the German Vacuum Tower telescope in Tenerife. The recorded data revealed a stable, bright structure of 3–4 arcsec size present during the whole 2.5 h of observations. We compare the velocity fields extracted by means of a λ-meter method and temperature and pressure stratification obtained after inversion of the profiles related to granules, intergranular lanes, and the plume. Results. The following results were obtained: (i) the correlation between variations in convective velocity and intensity in the plume is close to zero at all observed heights; (ii) the velocity flow in the plume changes from a downflow in the deep layers to an upflow in the upper layers; (iii) the brightness of the plume increases with height; (iv) the amplitudes of the five-minute oscillations of intensity and velocity are twice lower in the plume than outside, and vertically propagating waves are observed; (v) the plume is hotter and denser than the quiet Sun in the upper photosphere. Conclusions. We conclude that the observed phenomenon has a non-convective origin. The decrease in the amplitudes of oscillations in the plume cannot be attributed to the higher density in comparison to the surrounding atmosphere. Along with other findings, this indicates the possible presence of magnetic field. more...

The results of the determination of magnetic field strength from weak polarimetric signals in solar internetwork regions are contradictory. We investigate the origin of this contradiction with the help of MHD simulations. It is shown that the Stokes V amplitude ratio of the Fe I λλ15652-15648 lines is a good indicator of kG magnetic field concentrations, even for magnetic fields with a complex internal structure like those in MHD simulations. The Stokes V amplitude ratio of the Fe I λλ5247-5250 lines also shows a good correlation with magnetic field strength. However, in simulations with a flux level appropriate for the internetwork, it gives values corresponding to sub-kG fields. The reason is the rapid decrease of the field strength with height in kG magnetic field concentrations. These lines sample high regions of the atmosphere, where the field is already below kG levels. We also find that the Stokes V amplitude ratio of the Fe I λλ6301-6302 lines shows no correlation with the magnetic field strength. The reason lies in the large difference in the heights of formation of these two lines. The value of the magnetic field strength obtained from the Fe I λλ6301 and 6302 lines depends crucially on the treatment of gradients of the magnetic field, line-of-sight velocity, and temperature, even at a numerical spatial resolution of 20 km. more...

Large-amplitude longitudinal oscillations (LALOs) in prominences are spectacular manifestations of the solar activity. In such events nearby energetic disturbances induce periodic motions on filaments with displacements comparable to the size of the filaments themselves and with velocities larger than 20 km/s. The pendulum model, in which the gravity projected along a rigid magnetic field is the restoring force, was proposed to explain these events. However, it can be objected that in a realistic situation where the magnetic field reacts to the mass motion of the heavy prominence, the simplified pendulum model could be no longer valid. We have performed non-linear time-dependent numerical simulations of LALOs considering a dipped magnetic field line structure. In this work we demonstrate that for even relatively weak magnetic fields the pendulum model works very well. We therefore validate the pendulum model and show its robustness, with important implications for prominence seismology purposes. With this model it is possible to infer the geometry of the dipped field lines that support the prominence., Accepted for publication in The Astrophysical Journal more...

Recent high-resolution observations of sunspot oscillations using simultaneously operated ground- and space-based telescopes reveal the intrinsic connection between different layers of the solar atmosphere. However, it is not clear whether these oscillations are externally driven or generated in-situ. We address this question by using observations of propagating slow magneto-acoustic waves along a coronal fan loop system. In addition to the generally observed decreases in oscillation amplitudes with distance, the observed wave amplitudes are also found to be modulated with time, with similar variations observed throughout the propagation path of the wavetrain. Employing multi-wavelength and multi-instrument data we study the amplitude variations with time as the waves propagate through different layers of the solar atmosphere. By comparing the amplitude-modulation period in different layers, we find that slow magneto-acoustic waves observed in sunspots are externally driven by photospheric p-modes, which propagate upwards into the corona before becoming dissipated., Comment: accepted for publication in ApJ Letters more...

The amplitudes of the Evershed flow are measured using pairs of carefully selected FeI and FeII spectral lines located close in wavelength and registered simultaneously. A sunspot belonging to the NOAA 11582 group was scanned using the spectrograph of the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife). Velocities were extracted from intensity profiles using the lambda-meter technique. The formation heights of the observed spectral lines were calculated using semi-empirical models of a bright and dark penumbral filament taking into account the sunspot location at the limb. Our objective is to compare azimuthally averaged amplitudes of the Evershed flow extracted from neutral and ion lines. We find measurable differences in the radial component of the flow. All five pairs of lines show the same tendency, with a few hundred m/s larger amplitude of the flow measured from FeI lines compared to FeII lines. This tendency is preserved at all photospheric heights and radial distances in the penumbra. We discuss the possible origin of this effect., to appear in Astronomy and Astrophysics more...