On the Weakening of the Chromospheric Magnetic Field in Active Regions

Nagaraju, K.; Sankarasubramanian, K.; Rangarajan, K. E.

doi:10.1086/533433

Cited by 9 publications

(10 citation statements)

References 24 publications

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“…This inference recalls the publications where the photospheric and chromospheric magnetic fields were compared (Abramenko et al (1992), Choudhary et al (2002), Leka & Metcalf (2003), Balasubramaniam et al (2004); see also a resent review by Nagaraju et al (2008) and references in). Their results suggest that the stronger the line-of-sight magnetic field, the faster it decreases with height.…”

Section: Discussionsupporting

confidence: 71%

“…Their results suggest that the stronger the line-of-sight magnetic field, the faster it decreases with height. Nagaraju et al (2008) argued that for the photospheric field stronger than 700 G, the chromospheric field values "are much weaker than what one gets from the linear relationship [between the photospheric and chromospheric fields] and also from those expected from the extrapolation of the photospheric magnetic field" in the potential approximation. Leka & Metcalf (2003) observed that the potential field of NOAA 8299 extrapolated from the photosphere to reasonable heights (lower than 2 Mm) statistically exceeds the observed chromospheric field.…”

Section: Discussionmentioning

confidence: 99%

“…Several reasons were suggested to explain the effect (see Nagaraju et al (2008) for review). However, only one of them addresses the effect of horizontal electric current formation.…”

Section: Discussionmentioning

confidence: 99%

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Spectrum of Magnetic Dissipation and Horizontal Electric Currents in the Solar Photosphere

Abramenko

2008

Preprint

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A proxy for horizontal electric currents in the solar photosphere was suggested. For a set of evolving active regions (ARs) observed with Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager (MDI) in the high resolution mode, the dissipation spectrum, k 2 E(k), and the spatial structure of dissipation, i.e., the Stokes dissipation function ε(x, y), were calculated from the observed B z component of the magnetic field. These functions allowed us to calculate (a part of) the horizontal electric current density in the photosphere. It was shown that as an active region emerges, large-scale horizontal electric currents are gradually generated and determine a bulk of dissipation. When an active region decays, the large-scale horizontal currents decay faster than the small-scale ones. The density of horizontal currents in active regions is in the range of j h ∼ (0.008 − 0.028) A/m 2 , that is compatible with the density of vertical currents in active regions. We suggest two possible mechanisms for generation of such horizontal currents in the photosphere. One of them is the drift motions of charged particles in the medium of varying plasma pressure gradient in a horizontal plane at the periphery of a sunspot. Such a drift can produce quasi-circular closed horizontal currents around sunspots. Another possibility could be an existence of horizontal axial current inside a highly twisted horizontal magnetic structure laying in the photosphere along the magnetic neutral line. The horizontal currents may contribute significantly to the dynamics of the photosphere/corona coupling, as well as the estimation of non-potentiality of ARs.

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Section: Discussionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 99%

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Spectrum of Magnetic Dissipation and Horizontal Electric Currents in the Solar Photosphere

Abramenko

2008

Preprint

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“…Dual-beam polarimeters are becoming more and more popular among the astronomical community, such as the ones described by Packham et al (2005), Masiero et al (2008) and Nagaraju et al (2008). The high contrast ratios achieved by polarimetry make this technique a promising tool to characterize exoplanets as well as circumstellar environments.…”

Section: Resultsmentioning

confidence: 99%

Data-reduction techniques for high-contrast imaging polarimetry

Cánovas

Rodenhuis

Jeffers

et al. 2011

A&A

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Context. Imaging polarimetry is a powerful tool for detecting and characterizing exoplanets and circumstellar environments. Polarimetry allows a separation of the light coming from an unpolarized source such as a star and the polarized source such as a planet or a protoplanetary disk. Future facilities like SPHERE at the VLT or EPICS at the E-ELT will incorporate imaging polarimetry to detect exoplanets. The Extreme Polarimeter (ExPo) is a dual-beam imaging polarimeter that can currently reach contrast ratios of 10 5 , enough to characterize circumstellar environments. Aims. We present the data-reduction steps for a dual-beam imaging polarimeter that can reach contrast ratios of 10 5 . Methods. The data obtained with ExPo at the William Herschel Telescope (WHT) are analyzed. Instrumental artifacts and noise sources are discussed for an unpolarized star and for a protoplanetary disk (AB Aurigae).Results. The combination of fast modulation and dual-beam techniques allows us to minimize instrumental artifacts. A proper data processing and alignment of the images is fundamental when dealing with high contrasts. Imaging polarimetry proves to be a powerful method to resolve circumstellar environments even without a coronagraph mask or an adaptive optics system.

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“…Diagnosing chromospheric magnetic field 47 Inspite of its ubiquitous presence H α has been rarely used for probing chromospheric magnetic field. To mention a few, Abdusamatov & Karat (1971); Balasubramaniam et al (2004); Hanaoka (2005); Nagaraju et al (2008) have presented chromospheric magnetic field measurements through H α spectropolarimetry. One of the reasons for rarely using this line for magnetic field measurements is interpreting the observations is notoriously difficult.…”

Section: Introductionmentioning

confidence: 99%

Diagnosing chromospheric magnetic field through simultaneous spectropolarimetry in Hα and Ca II 854.2 nm

2019

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Measurement of magnetic field in this layer is challenging both from point of view of observations and interpretation of the data. We present in this work about spectropolarimetric observations of a pore, simultaneously in Ca ii (CaIR) at 854.2 nm (CaIR) and H α (656.28 nm). The observed region includes a small scale energetic event (SSEE) taking place in the region between the pore and the region which show opposite polarity to that of pore at the photosphere. The energetic event appears to be a progressive reconnection event as shown by the time evolution of the intensity profiles. Closer examination of the intensity profiles from the downflow regions suggest that the height of formation of CaIR is higher than that of Hi α, contrary to the current understanding about their height of formation. Preliminary results on the inversion of Stokes-I and V profiles of CaIR are also presented.

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On the Weakening of the Chromospheric Magnetic Field in Active Regions

Cited by 9 publications

References 24 publications

Spectrum of Magnetic Dissipation and Horizontal Electric Currents in the Solar Photosphere

Spectrum of Magnetic Dissipation and Horizontal Electric Currents in the Solar Photosphere

Data-reduction techniques for high-contrast imaging polarimetry

Diagnosing chromospheric magnetic field through simultaneous spectropolarimetry in Hα and Ca II 854.2 nm

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