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S K Solanki - One of the best experts on this subject based on the ideXlab platform.
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Impulsive coronal heating during the interaction of Surface magnetic fields in the lower Solar atmosphere
'EDP Sciences', 2020Co-Authors: L. P. Chitta, H. Peter, E. R. Priest, S K SolankiAbstract:Coronal plasma in the cores of Solar active regions is impulsively heated to more than 5 MK. The nature and location of the magnetic energy source responsible for such impulsive heating is poorly understood. Using observations of seven active regions from the Solar Dynamics Observatory, we found that a majority of coronal loops hosting hot plasma have at least one footpoint rooted in regions of interacting mixed magnetic polarity at the Solar Surface. In cases when co-temporal observations from the Interface Region Imaging Spectrograph space mission are available, we found spectroscopic evidence for magnetic reconnection at the base of the hot coronal loops. Our analysis suggests that interactions of magnetic patches of opposite polarity at the Solar Surface and the associated energy release during reconnection are key to impulsive coronal heating
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Solar magnetoconvection and small scale dynamo recent developments in observation and simulation
Space Science Reviews, 2017Co-Authors: J M Borrero, S K Solanki, M. Schüssler, Shahin JafarzadehAbstract:A number of observational and theoretical aspects of Solar magnetoconvection are considered in this review. We discuss recent developments in our understanding of the small-scale structure of the magnetic field on the Solar Surface and its interaction with convective flows, which is at the centre of current research. Topics range from plage areas in active regions over the magnetic network shaped by supergranulation to the ubiquituous ‘turbulent’ internetwork fields. On the theoretical side, we focus upon magnetic field generation by small-scale dynamo action.
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point spread function of sdo hmi and the effects of stray light correction on the apparent properties of Solar Surface phenomena
Astronomy and Astrophysics, 2014Co-Authors: K L Yeo, S K Solanki, A Feller, S Couvidat, S Danilovic, Natalie A KrivovaAbstract:Aims. We present a point spread function (PSF) for the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and discuss the effects of its removal on the apparent properties of Solar Surface phenomena in HMI data. Methods. The PSF was retrieved from observations of Venus in transit by matching it to the convolution of a model of the Venusian disc and Solar background with a guess PSF. We described the PSF as the sum of five Gaussian functions, the amplitudes of which vary sinusoidally with azimuth. This relatively complex functional form was required by the data. Observations recorded near in time to the transit of Venus were corrected for instrumental scattered light by the deconvolution with the PSF. We also examined the variation in the shape of the Solar aureole in daily data, as an indication of PSF changes over time. Results. Granulation contrast in restored HMI data is greatly enhanced relative to the original data and exhibit reasonable agreement with numerical simulations. Image restoration enhanced the apparent intensity and pixel averaged magnetic field strength of photospheric magnetic features significantly. For small-scale magnetic features, restoration enhanced intensity contrast in the continuum and core of the Fe I 6173 A line by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For sunspots and pores, the enhancement varied strongly within and between features, being more acute for smaller features. Magnetic features are also rendered smaller, as signal smeared onto the surrounding quiet Sun is recovered. Image restoration increased the apparent amount of magnetic flux above the noise floor by a factor of about 1.2, most of the gain coming from the quiet Sun. Line-of-sight velocity due to granulation and supergranulation is enhanced by a factor of 1.4 to 2.1, depending on position on the Solar disc. The shape of the Solar aureole varied, with time and between the two CCDs. There are also indications that the PSF varies across the FOV. However, all these variations were found to be relatively small, such that a single PSF can be applied to HMI data from both CCDs, over the period examined without introducing significant error. Conclusions. Restoring HMI observations with the PSF presented here returns a reasonable estimate of the stray light-free intensity contrast. Image restoration affects the measured radiant, magnetic and dynamic properties of Solar Surface phenomena sufficiently to significantly impact interpretation.
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point spread function of sdo hmi and the effects of stray light correction on the apparent properties of Solar Surface phenomena
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: K L Yeo, S K Solanki, A Feller, S Couvidat, S Danilovic, Natalie A KrivovaAbstract:We present a PSF for SDO/HMI and discuss the effects of its removal on the apparent properties of Solar Surface phenomena in HMI data. The PSF was retrieved from observations of Venus in transit by matching it to the convolution of a model of the venusian disc and Solar background with a guess PSF. Observations recorded near in time to the transit of Venus were corrected for instrumental scattered light by the deconvolution with the PSF. Granulation contrast in restored HMI data is greatly enhanced relative to the original data and exhibit reasonable agreement with numerical simulations. Image restoration enhanced the apparent intensity and pixel averaged magnetic field strength of photospheric magnetic features significantly. For small-scale magnetic features, restoration enhanced intensity contrast in the continuum and core of the Fe I 617.3 nm line by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For sunspots and pores, the enhancement varied strongly within and between features, being more acute for smaller features. Magnetic features are also rendered smaller, as signal smeared onto the surrounding quiet Sun is recovered. Image restoration increased the apparent amount of magnetic flux above the noise floor by a factor of about 1.2, most of the gain coming from the quiet Sun. Line-of-sight velocity due to granulation and supergranulation is enhanced by a factor of 1.4 to 2.1, depending on position on the Solar disc. There are indications that the PSF varies across the FOV, with time and between the two CCDs. However, all these variations were found to be relatively small, such that the derived PSF can be applied to HMI data from both CCDs, over the period examined without introducing significant error. Image restoration affects the measured radiant, magnetic and dynamic properties of Solar Surface phenomena sufficiently to significantly impact interpretation.
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analyzing Solar cycles
Science, 2011Co-Authors: S K Solanki, Natalie A KrivovaAbstract:Since observational records began about 300 years ago, and very likely for millions of years before that, the Sun has displayed cyclically varying magnetic activity ( 1 ). Approximately every 11 years, a maximum of activity is reached, with a large number of sunspots (see the figure, panel A) present on the Solar Surface, strong x-ray emission from the corona, and a peak in the number of flares and coronal mass ejections. The latter cause mid- and low-latitude aurorae, disrupt radio communications, perturb navigation systems and radars, produce electric power outages, and can pose radiation hazards for astronauts and aircraft crew.
M. Schüssler - One of the best experts on this subject based on the ideXlab platform.
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Solar magnetoconvection and small scale dynamo recent developments in observation and simulation
Space Science Reviews, 2017Co-Authors: J M Borrero, S K Solanki, M. Schüssler, Shahin JafarzadehAbstract:A number of observational and theoretical aspects of Solar magnetoconvection are considered in this review. We discuss recent developments in our understanding of the small-scale structure of the magnetic field on the Solar Surface and its interaction with convective flows, which is at the centre of current research. Topics range from plage areas in active regions over the magnetic network shaped by supergranulation to the ubiquituous ‘turbulent’ internetwork fields. On the theoretical side, we focus upon magnetic field generation by small-scale dynamo action.
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effects of the scatter in sunspot group tilt angles on the large scale magnetic field at the Solar Surface
The Astrophysical Journal, 2014Co-Authors: J Jiang, R H Cameron, M. SchüsslerAbstract:The tilt angles of sunspot groups represent the poloidal field source in Babcock-Leighton-type models of the Solar dynamo and are crucial for the build-up and reversals of the polar fields in Surface flux transport (SFT) simulations. The evolution of the polar field is a consequence of Hale's polarity rules, together with the tilt angle distribution which has a systematic component (Joy's law) and a random component (tilt-angle scatter). We determine the scatter using the observed tilt angle data and study the effects of this scatter on the evolution of the Solar Surface field using SFT simulations with flux input based upon the recorded sunspot groups. The tilt angle scatter is described in our simulations by a random component according to the observed distributions for different ranges of sunspot group size (total umbral area). By performing simulations with a number of different realizations of the scatter we study the effect of the tilt angle scatter on the global magnetic field, especially on the evolution of the axial dipole moment. The average axial dipole moment at the end of cycle 17 (a medium-amplitude cycle) from our simulations was 2.73 G. The tilt angle scatter leads to an uncertainty of 0.78 G (standard deviation). We also considered cycle 14 (a weak cycle) and cycle 19 (a strong cycle) and show that the standard deviation of the axial dipole moment is similar for all three cycles. The uncertainty mainly results from the big sunspot groups which emerge near the equator. In the framework of Babcock-Leighton dynamo models, the tilt angle scatter therefore constitutes a significant random factor in the cycle-to-cycle amplitude variability, which strongly limits the predictability of Solar activity.
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decay of a simulated mixed polarity magnetic field in the Solar Surface layers
Astronomy and Astrophysics, 2011Co-Authors: R H Cameron, A Vogler, M. SchüsslerAbstract:Magnetic flux is continuously being removed and replenished on the Solar Surface. To understand the removal process we carried out 3D radiative MHD simulations of the evolution of patches of photospheric magnetic field with equal amounts of positive and negative flux. We find that the flux is removed at a rate corresponding to an effective turbulent diffusivity, ηeff, of 100−340 km 2 s −1 , depending on the boundary conditions. For average unsigned flux densities above about 70 Gauss, the percentage of Surface magnetic energy coming from different field strengths is almost invariant. The overall process is then one where magnetic elements are advected by the horizontal granular motions and occasionally come into contact with opposite-polarity elements. These reconnect above the photosphere on a comparatively short time scale after which the U loops produced rapidly escape through the upper Surface while the downward retraction of inverse-U loops is significantly slower, because of the higher inertia and lower plasma beta in the deeper layers.
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Vortices in simulations of Solar Surface convection
'EDP Sciences', 2011Co-Authors: R. Moll, R H Cameron, M. SchüsslerAbstract:We report on the occurrence of small-scale vortices in simulations of the convective Solar Surface. Using an eigenanalysis of the velocity gradient tensor, we find the subset of high-vorticity regions in which the plasma is swirling. The swirling regions form an unsteady, tangled network of filaments in the turbulent downflow lanes. Near-Surface vertical vortices are underdense and cause a local depression of the optical Surface. They are potentially observable as bright points in the dark intergranular lanes. Vortex features typically exist for a few minutes, during which they are moved and twisted by the motion of the ambient plasma. The bigger vortices found in the simulations are possibly, but not necessarily, related to observations of granular-scale spiraling pathlines in “cork animations” or feature tracking
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Solar Surface emerging flux regions a comparative study of radiative mhd modeling and hinode sot observations
The Astrophysical Journal, 2008Co-Authors: Mark C M Cheung, M. Schüssler, T D Tarbell, Alan M TitleAbstract:We present results from numerical modeling of emerging flux regions on the Solar Surface. The modeling was carried out by means of three-dimensional (3D) radiative MHD simulations of the rise of buoyant magnetic flux tubes through the convection zone and into the photosphere. Due to the strong stratification of the convection zone, the rise results in a lateral expansion of the tube into a magnetic sheet, which acts as a reservoir for small-scale flux emergence events at the scale of granulation. The interaction of the convective downflows and the rising magnetic flux tube undulates it to form serpentine field lines that emerge into the photosphere. Observational characteristics, including the pattern of the emerging flux regions, the cancellation of Surface flux and associated high-speed downflows, the convective collapse of photospheric flux tubes, the appearance of anomalous darkenings, the formation of bright points, and the possible existence of transient kilogauss horizontal fields are discussed in the context of new observations from the Hinode Solar Optical Telescope. Implications for the local helioseismology of emerging flux regions are also discussed.
Mj Thompson - One of the best experts on this subject based on the ideXlab platform.
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acoustic wave propagation in the Solar sub photosphere with localised magnetic field concentration effect of magnetic tension
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Sergiy Shelyag, Sergei Zharkov, V Fedun, R Erdelyi, Mj ThompsonAbstract:Aims. In this paper we analyse numerically the propagation and dispersion of acoustic waves in the Solar-like sub-photosphere with localised non-uniform magnetic field concentrations, mimicking sunspots with various representative magnetic field configurations. Methods. Numerical simulations of wave propagation through the Solar sub-photosphere with a localised magnetic field concentration are carried out using SAC, which solves the MHD equations for gravitationally stratified plasma. The initial equilibrium density and pressure stratifications are derived from a standard Solar model. Acoustic waves are generated by a source located at the height approximately corresponding to the visible Surface of the Sun. We analyse the response of vertical velocity to changes in the interior due to magnetic field at the level corresponding to the visible Solar Surface, by the means of local time-distance helioseismology. Results. The results of numerical simulations of acoustic wave propagation and dispersion in the Solar sub-photosphere with localised magnetic field concentrations of various types are presented. Time-distance diagrams of the vertical velocity perturbation at the level corresponding to the visible Solar Surface show that the magnetic field perturbs and scatters acoustic waves and absorbs the acoustic power of the wave packet. For the weakly magnetised case the effect of magnetic field is mainly thermodynamic, since the magnetic field changes the temperature stratification. However, we observe the signature of slow magnetoacoustic mode, propagating downwards, for the strong magnetic field cases.
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Acoustic wave propagation in the Solar sub-photosphere with localised magnetic field concentration: effect of magnetic tension
ASTRON ASTROPHYS, 2009Co-Authors: Mj ThompsonAbstract:Aims. We analyse numerically the propagation and dispersion of acoustic waves in the Solar-like sub-photosphere with localised nonuniform magnetic field concentrations, mimicking sunspots with various representative magnetic field configurations.Methods. Numerical simulations of wave propagation through the Solar sub-photosphere with a localised magnetic field concentration are carried out using SAC, which solves the MHD equations for gravitationally stratified plasma. The initial equilibrium density and pressure stratifications are derived from a standard Solar model. Acoustic waves are generated by a source located at the height corresponding approximately to the visible Surface of the Sun. By means of local helioseismology we analyse the response of vertical velocity at the level corresponding to the visible Solar Surface to changes induced by magnetic field in the interior.Results. The results of numerical simulations of acoustic wave propagation and dispersion in the Solar sub-photosphere with localised magnetic field concentrations of various types are presented. Time-distance diagrams of the vertical velocity perturbation at the level corresponding to the visible Solar Surface show that the magnetic field perturbs and scatters acoustic waves and absorbs the acoustic power of the wave packet. For the weakly magnetised case, the effect of magnetic field is mainly thermodynamic, since the magnetic field changes the temperature stratification. However, we observe the signature of slow magnetoacoustic mode, propagating downwards, for the strong magnetic field cases.
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forward modeling of acoustic wave propagation in the quiet Solar subphotosphere
The Astrophysical Journal, 2006Co-Authors: Sergiy Shelyag, R Erdelyi, Mj ThompsonAbstract:The results of numerical simulations of acoustic wave propagation and dispersion in the nonmagnetic Solar subphotosphere are presented. Initial equilibrium density and pressure stratifications are taken from a standard Solar model but modified to suppress convective instabilities in fully compressible two-dimensional ideal hydrodynamical modeling. Acoustic waves are generated by sources located below the height corresponding to the visible Solar Surface. The dynamic response of the Solar interior to two acoustic source types, namely a harmonic source and one representing downward-propagating photospheric plumes, is studied. A large number of randomly distributed localized cooling sources with random amplitudes is also introduced. The methods used to analyze the simulation data are similar to ones used in observational studies in local helioseismology. Time-distance diagrams of the pressure and vertical velocity perturbations at the level corresponding to the Solar Surface show the appearance of wave packets propagating with different speeds, which are reflected at different depths beneath the subphotosphere. The (ω, kh) power spectra, derived from the vertical velocity data, show the existence of g-, f-, and p-modes; p-mode ridges are identifiable up to high radial orders of n ≈ 11; g-modes appear in the simulations, unlike in the real Sun, where they cannot propagate in the convectively unstable Solar subphotosphere. Cross-correlation analysis of vertical velocity perturbations shows a good correspondence with the observed time-distance helioseismic data for quiet Sun. Thus, the ability of the implemented approach of forward modeling to investigate propagation of acoustic, internal, and Surface gravity waves in a realistic Solar interior model is shown.
Natalie A Krivova - One of the best experts on this subject based on the ideXlab platform.
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point spread function of sdo hmi and the effects of stray light correction on the apparent properties of Solar Surface phenomena
Astronomy and Astrophysics, 2014Co-Authors: K L Yeo, S K Solanki, A Feller, S Couvidat, S Danilovic, Natalie A KrivovaAbstract:Aims. We present a point spread function (PSF) for the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and discuss the effects of its removal on the apparent properties of Solar Surface phenomena in HMI data. Methods. The PSF was retrieved from observations of Venus in transit by matching it to the convolution of a model of the Venusian disc and Solar background with a guess PSF. We described the PSF as the sum of five Gaussian functions, the amplitudes of which vary sinusoidally with azimuth. This relatively complex functional form was required by the data. Observations recorded near in time to the transit of Venus were corrected for instrumental scattered light by the deconvolution with the PSF. We also examined the variation in the shape of the Solar aureole in daily data, as an indication of PSF changes over time. Results. Granulation contrast in restored HMI data is greatly enhanced relative to the original data and exhibit reasonable agreement with numerical simulations. Image restoration enhanced the apparent intensity and pixel averaged magnetic field strength of photospheric magnetic features significantly. For small-scale magnetic features, restoration enhanced intensity contrast in the continuum and core of the Fe I 6173 A line by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For sunspots and pores, the enhancement varied strongly within and between features, being more acute for smaller features. Magnetic features are also rendered smaller, as signal smeared onto the surrounding quiet Sun is recovered. Image restoration increased the apparent amount of magnetic flux above the noise floor by a factor of about 1.2, most of the gain coming from the quiet Sun. Line-of-sight velocity due to granulation and supergranulation is enhanced by a factor of 1.4 to 2.1, depending on position on the Solar disc. The shape of the Solar aureole varied, with time and between the two CCDs. There are also indications that the PSF varies across the FOV. However, all these variations were found to be relatively small, such that a single PSF can be applied to HMI data from both CCDs, over the period examined without introducing significant error. Conclusions. Restoring HMI observations with the PSF presented here returns a reasonable estimate of the stray light-free intensity contrast. Image restoration affects the measured radiant, magnetic and dynamic properties of Solar Surface phenomena sufficiently to significantly impact interpretation.
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point spread function of sdo hmi and the effects of stray light correction on the apparent properties of Solar Surface phenomena
arXiv: Solar and Stellar Astrophysics, 2013Co-Authors: K L Yeo, S K Solanki, A Feller, S Couvidat, S Danilovic, Natalie A KrivovaAbstract:We present a PSF for SDO/HMI and discuss the effects of its removal on the apparent properties of Solar Surface phenomena in HMI data. The PSF was retrieved from observations of Venus in transit by matching it to the convolution of a model of the venusian disc and Solar background with a guess PSF. Observations recorded near in time to the transit of Venus were corrected for instrumental scattered light by the deconvolution with the PSF. Granulation contrast in restored HMI data is greatly enhanced relative to the original data and exhibit reasonable agreement with numerical simulations. Image restoration enhanced the apparent intensity and pixel averaged magnetic field strength of photospheric magnetic features significantly. For small-scale magnetic features, restoration enhanced intensity contrast in the continuum and core of the Fe I 617.3 nm line by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For sunspots and pores, the enhancement varied strongly within and between features, being more acute for smaller features. Magnetic features are also rendered smaller, as signal smeared onto the surrounding quiet Sun is recovered. Image restoration increased the apparent amount of magnetic flux above the noise floor by a factor of about 1.2, most of the gain coming from the quiet Sun. Line-of-sight velocity due to granulation and supergranulation is enhanced by a factor of 1.4 to 2.1, depending on position on the Solar disc. There are indications that the PSF varies across the FOV, with time and between the two CCDs. However, all these variations were found to be relatively small, such that the derived PSF can be applied to HMI data from both CCDs, over the period examined without introducing significant error. Image restoration affects the measured radiant, magnetic and dynamic properties of Solar Surface phenomena sufficiently to significantly impact interpretation.
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analyzing Solar cycles
Science, 2011Co-Authors: S K Solanki, Natalie A KrivovaAbstract:Since observational records began about 300 years ago, and very likely for millions of years before that, the Sun has displayed cyclically varying magnetic activity ( 1 ). Approximately every 11 years, a maximum of activity is reached, with a large number of sunspots (see the figure, panel A) present on the Solar Surface, strong x-ray emission from the corona, and a peak in the number of flares and coronal mass ejections. The latter cause mid- and low-latitude aurorae, disrupt radio communications, perturb navigation systems and radars, produce electric power outages, and can pose radiation hazards for astronauts and aircraft crew.
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Solar Surface Magnetism and Irradiance on Time Scales from Days to the 11-Year Cycle
Space Science Reviews, 2009Co-Authors: V. Domingo, Natalie A Krivova, S K Solanki, I. Ermolli, C. Fröhlich, M. Haberreiter, G. Kopp, W. Schmutz, H. C. Spruit, Y. UnruhAbstract:The uninterrupted measurement of the total Solar irradiance during the last three Solar cycles and an increasing amount of Solar spectral irradiance measurements as well as Solar imaging observations (magnetograms and photometric data) have stimulated the development of models attributing irradiance variations to Solar Surface magnetism. Here we review the current status of Solar irradiance measurements and modelling efforts based on Solar photospheric magnetic fields. Thereby we restrict ourselves to the study of Solar variations from days to the Solar cycle. Phenomenological models of the Solar atmosphere in combination with imaging observations of Solar electromagnetic radiation and measurements of the photospheric magnetic field have reached high enough quality to show that a large fraction (at least, about 80%) of the Solar irradiance variability can be explained by the radiative effects of the magnetic activity present in the photosphere. Also, significant progress has been made with magnetohydrodynamic simulations of convection that allow us to relate the radiance of the photospheric magnetic structures to the observations.
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reconstruction of Solar irradiance variations in cycle 23 is Solar Surface magnetism the cause
Astronomy and Astrophysics, 2003Co-Authors: Natalie A Krivova, S K Solanki, M Fligge, Y C UnruhAbstract:A model of Solar irradiance variations is presented which is based on the assumption that Solar Surface magnetism is responsible for all total irradiance changes on time scales of days to years. A time series of daily magnetograms and empirical models of the thermal structure of magnetic features (sunspots, faculae) are combined to reconstruct total (and spectral) irra- diance from 1996 to 2002. Comparisons with observational data reveal an excellent correspondence, although the model only contains a single free parameter. This provides strong support for the hypothesis that Solar irradiance variations are caused by changes in the amount and distribution of magnetic flux at the Solar Surface.
Sergiy Shelyag - One of the best experts on this subject based on the ideXlab platform.
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acoustic wave propagation in the Solar sub photosphere with localised magnetic field concentration effect of magnetic tension
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Sergiy Shelyag, Sergei Zharkov, V Fedun, R Erdelyi, Mj ThompsonAbstract:Aims. In this paper we analyse numerically the propagation and dispersion of acoustic waves in the Solar-like sub-photosphere with localised non-uniform magnetic field concentrations, mimicking sunspots with various representative magnetic field configurations. Methods. Numerical simulations of wave propagation through the Solar sub-photosphere with a localised magnetic field concentration are carried out using SAC, which solves the MHD equations for gravitationally stratified plasma. The initial equilibrium density and pressure stratifications are derived from a standard Solar model. Acoustic waves are generated by a source located at the height approximately corresponding to the visible Surface of the Sun. We analyse the response of vertical velocity to changes in the interior due to magnetic field at the level corresponding to the visible Solar Surface, by the means of local time-distance helioseismology. Results. The results of numerical simulations of acoustic wave propagation and dispersion in the Solar sub-photosphere with localised magnetic field concentrations of various types are presented. Time-distance diagrams of the vertical velocity perturbation at the level corresponding to the visible Solar Surface show that the magnetic field perturbs and scatters acoustic waves and absorbs the acoustic power of the wave packet. For the weakly magnetised case the effect of magnetic field is mainly thermodynamic, since the magnetic field changes the temperature stratification. However, we observe the signature of slow magnetoacoustic mode, propagating downwards, for the strong magnetic field cases.
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forward modeling of acoustic wave propagation in the quiet Solar subphotosphere
The Astrophysical Journal, 2006Co-Authors: Sergiy Shelyag, R Erdelyi, Mj ThompsonAbstract:The results of numerical simulations of acoustic wave propagation and dispersion in the nonmagnetic Solar subphotosphere are presented. Initial equilibrium density and pressure stratifications are taken from a standard Solar model but modified to suppress convective instabilities in fully compressible two-dimensional ideal hydrodynamical modeling. Acoustic waves are generated by sources located below the height corresponding to the visible Solar Surface. The dynamic response of the Solar interior to two acoustic source types, namely a harmonic source and one representing downward-propagating photospheric plumes, is studied. A large number of randomly distributed localized cooling sources with random amplitudes is also introduced. The methods used to analyze the simulation data are similar to ones used in observational studies in local helioseismology. Time-distance diagrams of the pressure and vertical velocity perturbations at the level corresponding to the Solar Surface show the appearance of wave packets propagating with different speeds, which are reflected at different depths beneath the subphotosphere. The (ω, kh) power spectra, derived from the vertical velocity data, show the existence of g-, f-, and p-modes; p-mode ridges are identifiable up to high radial orders of n ≈ 11; g-modes appear in the simulations, unlike in the real Sun, where they cannot propagate in the convectively unstable Solar subphotosphere. Cross-correlation analysis of vertical velocity perturbations shows a good correspondence with the observed time-distance helioseismic data for quiet Sun. Thus, the ability of the implemented approach of forward modeling to investigate propagation of acoustic, internal, and Surface gravity waves in a realistic Solar interior model is shown.
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why Solar magnetic flux concentrations are bright in molecular bands
The Astrophysical Journal, 2003Co-Authors: M. Schüssler, A Vogler, Sergiy Shelyag, S V Berdyugina, S K SolankiAbstract:Using realistic ab initio simulations of radiative magnetoconvection, we show that the bright structures in images taken in the "G band," a spectral band dominated by lines of the CH molecule, precisely outline small-scale concentrations of strong magnetic fields on the visible Solar Surface. The brightening is caused by a depletion of CH molecules in the hot and tenuous magnetic structures, thus confirming the model of radiatively heated magnetic flux concentrations. These results provide a firm basis for observational studies of the evolution and dynamics of the small-scale Solar magnetic field derived through "proxy magnetometry" with G-band images.
