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M Collados - One of the best experts on this subject based on the ideXlab platform.
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temporal evolution of small scale internetwork magnetic fields in the Solar Photosphere
Astronomy and Astrophysics, 2021Co-Authors: R J Campbell, C. J. Nelson, M Collados, M Mathioudakis, Peter H Keys, Andres Asensio Ramos, D KuridzeAbstract:Context. While the longitudinal field that dominates in photospheric network regions has been studied extensively, small-scale transverse fields have recently been found to be ubiquitous in the quiet internetwork Photosphere and this merits further study. Furthermore, few observations have been able to capture how this field evolves. Aims. We aim to statistically characterize the magnetic vector in a quiet Sun internetwork region and observe the temporal evolution of specific small-scale magnetic features. Methods. We present two high spatio-temporal resolution observations that reveal the dynamics of two disk-centre internetwork regions taken by the new GREGOR Infrared Spectrograph Integral Field Unit with the highly magnetically sensitive photospheric Fe I line pair at 15648.52 A and 15652.87 A. We record the full Stokes vector and apply inversions with the Stokes inversions based on response functions code to retrieve the parameters characterizing the atmosphere. We consider two inversion schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in a field free medium, and scheme 2 (S2), with two magnetic models and a fixed 30% stray light component. Results. The magnetic properties produced from S1 inversions returned a median magnetic field strength of 200 and 240 G for the two datasets, respectively. We consider the median transverse (horizontal) component, among pixels with Stokes Q or U, and the median unsigned longitudinal (vertical) component, among pixels with Stokes V, above a noise threshold. We determined the former to be 263 G and 267 G, and the latter to be 131 G and 145 G, for the two datasets, respectively. Finally, we present three regions of interest, tracking the dynamics of small-scale magnetic features. We apply S1 and S2 inversions to specific profiles of interest and find that the latter produces better approximations when there is evidence of mixed polarities. We find patches of linear polarization with magnetic flux density of the order of 130-150 G and find that linear polarization appears preferentially at granule-intergranular lane boundaries. The weak magnetic field appears to be organized in terms of complex 'loop-like' structures, with transverse fields often flanked by opposite polarity longitudinal fields.
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channeling 5 minute photospheric oscillations into the Solar outer atmosphere through small scale vertical magnetic flux tubes
The Astrophysical Journal, 2008Co-Authors: E Khomenko, M Collados, R Centeno, Trujillo J BuenoAbstract:We report two-dimensional MHD simulations which demonstrate that photospheric 5 minute 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 cutoff frequency and may allow for the propagation of the 5 minute waves vertically into the chromosphere.
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channeling 5 min photospheric oscillations into the Solar outer atmosphere through small scale vertical magnetic flux tubes
arXiv: Astrophysics, 2008Co-Authors: E Khomenko, M Collados, R Centeno, Trujillo J BuenoAbstract: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.
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a near infrared line of mn i as a diagnostic tool of the average magnetic energy in the Solar Photosphere
The Astrophysical Journal, 2007Co-Authors: Asensio A Ramos, M Martinez J Gonzalez, Lopez A Ariste, Trujillo J Bueno, M ColladosAbstract:We report on spectropolarimetric observations of a near-IR line of Mn I located at 15262.702 A whose intensity and polarization profiles are very sensitive to the presence of hyperfine structure. A theoretical investigation of the magnetic sensitivity of this line uncovers several interesting properties. The most important one is that the presence of strong Paschen-Back perturbations due to the hyperfine structure produces an intensity line profile whose shape changes according to the absolute value of the magnetic field strength. A line ratio technique is developed from the intrinsic variations of the line profile. This line ratio technique is applied to spectropolarimetric observations of the quiet Solar Photosphere in order to explore the probability distribution function of the magnetic field strength. Particular attention is given to the quietest area of the observed field of view, which was encircled by an enhanced network region. A detailed theoretical investigation shows that the inferred distribution yields information on the average magnetic field strength and on the spatial scale at which the magnetic field is organized. A first estimation gives ~250 G for the mean field strength and a tentative value of ~0.4'' for the spatial scale at which the observed magnetic field is horizontally organized.
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A near-IR line of Mn I as a diagnostic tool of the average magnetic energy in the Solar Photosphere
The Astrophysical Journal, 2007Co-Authors: Asensio A Ramos, M. J. Martinez Gonzalez, A. López Ariste, J. Trujillo Bueno, M ColladosAbstract:We report on spectropolarimetric observations of a near-IR line of Mn I located at 15262.702 A whose intensity and polarization profiles are very sensitive to the presence of hyperfine structure. A theoretical investigation of the magnetic sensitivity of this line to the magnetic field uncovers several interesting properties. The most important one is that the presence of strong Paschen-Back perturbations due to the hyperfine structure produces an intensity line profile whose shape changes according to the absolute value of the magnetic field strength. A line ratio technique is developed from the intrinsic variations of the line profile. This line ratio technique is applied to spectropolarimetric observations of the quiet Solar Photosphere in order to explore the probability distribution function of the magnetic field strength. Particular attention is given to the quietest area of the observed field of view, which was encircled by an enhanced network region. A detailed theoretical investigation shows that the inferred distribution yields information on the average magnetic field strength and the spatial scale at which the magnetic field is organized. A first estimation gives ~250 G for the mean field strength and a tentative value of ~0.45" for the spatial scale at which the observed magnetic field is horizontally organized.
Bruce W. Lites - One of the best experts on this subject based on the ideXlab platform.
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Are Internetwork Magnetic Fields in the Solar Photosphere Horizontal or Vertical
The Astrophysical Journal, 2017Co-Authors: Bruce W. Lites, J. M. Borrero, Matthias Rempel, Sanja DanilovicAbstract:Using many observations obtained during 2007 with the Spectro-Polarimeter of the Hinode Solar Optical Telescope, we explore the angular distribution of magnetic fields in the quiet internetwork regions of the Solar Photosphere. Our work follows from the insight of Stenflo, who examined only linear polarization signals in photospheric lines, thereby avoiding complications of the analysis arising from the differing responses to linear and circular polarization. We identify and isolate regions of a strong polarization signal that occupy only a few percent of the observed quiet Sun area yet contribute most to the net linear polarization signal. The center-to-limb variation of the orientation of linear polarization in these strong signal regions indicates that the associated magnetic fields have a dominant vertical orientation. In contrast, the great majority of the Solar disk is occupied by much weaker linear polarization signals. The orientation of the linear polarization in these regions demonstrates that the field orientation is dominantly horizontal throughout the Photosphere. We also apply our analysis to Stokes profiles synthesized from the numerical MHD simulations of Rempel as viewed at various oblique angles. The analysis of the synthetic data closely follows that of the observations, lending confidence to using the simulations as a guide for understanding the physical origins of the center-to-limb variation of linear polarization in the quiet Sun area.
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The Hinode Spectro-Polarimeter
Solar Physics, 2013Co-Authors: Bruce W. Lites, D. L. Akin, G. Card, T. Cruz, D. Duncan, C. G. Edwards, D. F. Elmore, C. Hoffmann, Yukio Katsukawa, Noah KatzAbstract:The joint Japan/US/UK Hinode mission includes the first large-aperture visible-light Solar telescope flown in space. One component of the Focal Plane Package of that telescope is a precision spectro-polarimeter designed to measure full Stokes spectra with the intent of using those spectra to infer the magnetic-field vector at high precision in the Solar Photosphere. This article describes the characteristics of the flight hardware of the HinodeSpectro-Polarimeter, and summarizes its in-flight performance.
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The topology and behavior of magnetic fields emerging at the Solar Photosphere
Space Science Reviews, 2009Co-Authors: Bruce W. LitesAbstract:The nature of flux emerging through the surface layers of the Sun is examined in the light of new high-resolution magnetic field observations from the Hinode space mission. The combination of vector magnetic field data and visible-light imaging from Hinode support the hypothesis that active region filaments are created as a result of an emerging, twisted flux system. The observations do not present strong evidence for an alternate hypothesis: that the filaments form as a result of localized shear flows at the photospheric level. Examination of the vector magnetic field at very small scales in emerging flux regions suggests that reconnection at the photospheric level and below, followed by submergence of flux, is a likely and essential part of the flux emergence process. The reconnection and flux submergence are driven by granular convection.
C U Keller - One of the best experts on this subject based on the ideXlab platform.
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seething horizontal magnetic fields in the quiet Solar Photosphere
The Astrophysical Journal, 2007Co-Authors: J W Harvey, D Branston, C J Henney, C U KellerAbstract:The photospheric magnetic field outside of active regions and the network has a ubiquitous and dynamic line-of-sight component that strengthens from disk center to limb as expected for a nearly horizontal orientation. This component shows a striking time variation with an average temporal rms near the limb of 1.7 G at ~3'' resolution. In our moderate-resolution observations the nearly horizontal component has a frequency variation power-law exponent of -1.4 below 1.5 mHz and is spatially patchy on scales up to ~15''. The field may be a manifestation of changing magnetic connections between eruptions and evolution of small magnetic flux elements in response to convective motions. It shows no detectable latitude or longitude variations.
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seething horizontal magnetic fields in the quiet Solar Photosphere
arXiv: Astrophysics, 2007Co-Authors: J W Harvey, D Branston, C J Henney, C U Keller, Solis Team, Gong TeamAbstract:The photospheric magnetic field outside of active regions and the network has a ubiquitous and dynamic line-of-sight component that strengthens from disk center to limb as expected for a nearly horizontal orientation. This component shows a striking time variation with an average temporal rms near the limb of 1.7 G at ~3" resolution. In our moderate resolution observations the nearly horizontal component has a frequency variation power law exponent of -1.4 below 1.5 mHz and is spatially patchy on scales up to ~15 arcsec. The field may be a manifestation of changing magnetic connections between eruptions and evolution of small magnetic flux elements in response to convective motions. It shows no detectable latitude or longitude variations.
Matthias Rempel - One of the best experts on this subject based on the ideXlab platform.
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Transport of Internetwork Magnetic Flux Elements in the Solar Photosphere
The Astrophysical Journal, 2018Co-Authors: Piyush Agrawal, Luis R. Bellot Rubio, Mark Rast, Milan Gošić, Matthias RempelAbstract:The motions of small-scale magnetic flux elements in the Solar Photosphere can provide some measure of the Lagrangian properties of the convective flow. Measurements of these motions have been critical in estimating the turbulent diffusion coefficient in flux-transport dynamo models and in determining the Alfven wave excitation spectrum for coronal heating models. We examine the motions of internetwork flux elements in Hinode/Narrowband Filter Imager magnetograms and study the scaling of their mean squared displacement and the shape of their displacement probability distribution as a function of time. We find that the mean squared displacement scales super-diffusively with a slope of about 1.48. Super-diffusive scaling has been observed in other studies for temporal increments as small as 5 s, increments over which ballistic scaling would be expected. Using high-cadence MURaM simulations, we show that the observed super-diffusive scaling at short increments is a consequence of random changes in barycenter positions due to flux evolution. We also find that for long temporal increments, beyond granular lifetimes, the observed displacement distribution deviates from that expected for a diffusive process, evolving from Rayleigh to Gaussian. This change in distribution can be modeled analytically by accounting for supergranular advection along with granular motions. These results complicate the interpretation of magnetic element motions as strictly advective or diffusive on short and long timescales and suggest that measurements of magnetic element motions must be used with caution in turbulent diffusion or wave excitation models. We propose that passive tracer motions in measured photospheric flows may yield more robust transport statistics.
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transport of internetwork magnetic flux elements in the Solar Photosphere
arXiv: Solar and Stellar Astrophysics, 2017Co-Authors: Piyush Agrawal, Mark Rast, Milan Gosic, Luis Bellot R Rubio, Matthias RempelAbstract:The motions of small-scale magnetic flux elements in the Solar Photosphere can provide some measure of the Lagrangian properties of the convective flow. Measurements of these motions have been critical in estimating the turbulent diffusion coefficient in flux-transport dynamo models and in determining the Alfven wave excitation spectrum for coronal heating models. We examine the motions of internetwork flux elements in a 24 hour long Hinode/NFI magnetogram sequence with 90 second cadence, and study both the scaling of their mean squared displacement and the shape of their displacement probability distribution as a function of time. We find that the mean squared displacement scales super-diffusively with a slope of about 1.48. Super-diffusive scaling has been observed in other studies for temporal increments as small as 5 seconds, increments over which ballistic scaling would be expected. Using high-cadence MURaM simulations, we show that the observed super-diffusive scaling at short temporal increments is a consequence of random changes in the barycenter positions due to flux evolution. We also find that for long temporal increments, beyond granular lifetimes, the observed displacement distribution deviates from that expected for a diffusive process, evolving from Rayleigh to Gaussian. This change in the distribution can be modeled analytically by accounting for supergranular advection along with motions due to granulation. These results complicate the interpretation of magnetic element motions as strictly advective or diffusive on short and long timescales and suggest that measurements of magnetic element motions must be used with caution in turbulent diffusion or wave excitation models. We propose that passive trace motions in measured photospheric flows may yield more robust transport statistics.
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Are Internetwork Magnetic Fields in the Solar Photosphere Horizontal or Vertical
The Astrophysical Journal, 2017Co-Authors: Bruce W. Lites, J. M. Borrero, Matthias Rempel, Sanja DanilovicAbstract:Using many observations obtained during 2007 with the Spectro-Polarimeter of the Hinode Solar Optical Telescope, we explore the angular distribution of magnetic fields in the quiet internetwork regions of the Solar Photosphere. Our work follows from the insight of Stenflo, who examined only linear polarization signals in photospheric lines, thereby avoiding complications of the analysis arising from the differing responses to linear and circular polarization. We identify and isolate regions of a strong polarization signal that occupy only a few percent of the observed quiet Sun area yet contribute most to the net linear polarization signal. The center-to-limb variation of the orientation of linear polarization in these strong signal regions indicates that the associated magnetic fields have a dominant vertical orientation. In contrast, the great majority of the Solar disk is occupied by much weaker linear polarization signals. The orientation of the linear polarization in these regions demonstrates that the field orientation is dominantly horizontal throughout the Photosphere. We also apply our analysis to Stokes profiles synthesized from the numerical MHD simulations of Rempel as viewed at various oblique angles. The analysis of the synthetic data closely follows that of the observations, lending confidence to using the simulations as a guide for understanding the physical origins of the center-to-limb variation of linear polarization in the quiet Sun area.
A M Title - One of the best experts on this subject based on the ideXlab platform.
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the magnetic connection between the Solar Photosphere and the corona
The Astrophysical Journal, 2003Co-Authors: C J Schrijver, A M TitleAbstract:The Solar magnetic field that extends through the chromosphere into the corona is envisioned to fan out from strong flux concentrations located within the supergranular downflow lanes. That so-called network field appears to be surrounded by a mixed-polarity magnetic field with a scale comparable to that of the granulation. We argue that for an internetwork field with a magnitude of a few tens of Mx cm-2, as suggested by both observations and models, the commonly held notion of a wineglass-shaped magnetic canopy of network flux that fully encloses weakly magnetic regions below it is fundamentally wrong. We estimate that in the presence of such a relatively strong internetwork field, as much as half of the coronal field over very quiet Sun may be rooted in that mixed-polarity internetwork field throughout the supergranules rather than in the network flux concentrations, as assumed until now. A corresponding amount of flux forms collars of closed loops around the network concentrations, connecting network flux back down onto the internetwork field over distances of several thousand kilometers. Within such a geometry, the rapid evolution of the internetwork field may substantially affect coronal heating and the acceleration of the Solar wind. We discuss the potential consequences of these interacting network and internetwork fields for atmospheric heating, for wave propagation and the formation of acoustic shadows, and for the appearance of the near-surface Solar outer atmosphere.
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dispersal of magnetic flux in the quiet Solar Photosphere
The Astrophysical Journal, 1999Co-Authors: H J Hagenaar, C J Schrijver, A M Title, R A ShineAbstract:We study the random walk of magnetic flux concentrations on two sequences of high-resolution magnetograms, observed with the Michelson Doppler Imager on board SOHO. The flux contained in the concentrations ranges from |Φ|=1018 Mx to |Φ|=1019 Mx, with an average of |Φ|=2.5×1018 Mx. Larger concentrations tend to move slower and live longer than smaller ones. On short timescales, the observed mean-square displacements are consistent with a random walk, characterized by a diffusion coefficient D(t 30 ks)=200-250 km2 s−1, approaching the measurements for a five-day set of Big Bear magnetograms, D250 km2 s−1. The transition between the low and large diffusion coefficients is explained with a model and simulations of the motions of test particles, subject to random displacements on both the granular and supergranular scales, simultaneously. In this model, the supergranular flow acts as a negligible drift on short timescale, but dominates the granular diffusion on longer timescales. We also investigate the possibility that concentrations are temporarily confined, as if they were caught in supergranular vertices, that form short-lived, relatively stable environments. The best agreement of model and data is found for step lengths of 0.5 and 8.5 Mm, associated evolution times of 14 minutes and 24 hr, and a confinement time of no more than a few hours. On our longest timescale, DSim(t>105)→285 km2 s−1, which is the sum of the small- and large-scale diffusion coefficients. Models of random walk diffusion on the Solar surface require a larger value: DWang=600±200 km2 s−1. One possible explanation for the difference is a bias in our measurements to the longest lived, and therefore slower concentrations in our data sets. Another possibility is the presence of an additional, much larger diffusive scale.
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On the differences between plage and quiet sun in the Solar Photosphere
The Astrophysical Journal, 1992Co-Authors: A M Title, K. P. Topka, Theodore D. Tarbell, Wolfgang Schmidt, Christiaan Balke, Göran B. ScharmerAbstract:Time sequences of interleaved observations of the continuum intensity, longitudinal magnetic field, vertical velocity in the midPhotosphere, and the line-center intensity in Ni I 6768 A were obtained in an active-region plage and the surrounding relatively field-free area near disk center. Spacetime Fourier filtering techniques are used to separate the convective and oscillatory components of the Solar atmosphere. The properties of the Photosphere are found to differ qualitatively and quantitatively between the plage, where the field is 150 G or more, and its quiet surroundings. The scale of granulation is smaller, the contrast lower, and the temporal evolution slower in the plage than the quiet sun. In the plage, the vertical velocity is reduced in amplitude compared to the quiet sun, and there is little evidence of a granulation pattern, while in the quiet sun the vertical flow pattern is similar in size and shape to the underlying granulation pattern in the continuum.
