Response of Hinode XRT to quiet Sun, active region and flare plasma

A method to separate the active region and quiet network components of the magnetic fields in the photosphere is described and compared with the corresponding measurements of the He I λ 10830 absorption. The relation between the total He I absorption and total magnetic flux in active regions is roughly linear and differs between cycles 21 and 22. There appears to no relation between these two quantities in areas outside of active regions. The total He I absorption in the quiet Sun (comprised of network, filaments, and coronal holes) exceeds that in active regions at all times during the cycle. As a whole, active regions of cycle 22 appear to be less complex than the active regions of cycle 21, hinting at one possible cause for a differing relation between spectral-irradiance variations and the underlying magnetic flux for these two cycles.

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Statistical study of photospheric bright points in an active region and quiet Sun

Astrophysics and Space Science ◽

10.1007/s10509-013-1555-6 ◽

2013 ◽

Vol 348 (1) ◽

pp. 17-24 ◽

Cited By ~ 20

Author(s):

Song Feng ◽

Linhua Deng ◽

Yunfei Yang ◽

Kaifan Ji

Keyword(s):

Active Region ◽

Statistical Study ◽

Quiet Sun

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Ubiquitous hundred-Gauss magnetic fields in solar spicules

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038546 ◽

2020 ◽

Vol 642 ◽

pp. A61

Author(s):

M. Kriginsky ◽

R. Oliver ◽

N. Freij ◽

D. Kuridze ◽

A. Asensio Ramos ◽

...

Keyword(s):

Magnetic Field ◽

Active Region ◽

Magnetic Fields ◽

Field Approximation ◽

Weak Field ◽

Field Polarity ◽

Statistical Point ◽

Quiet Sun ◽

Solar Spicules ◽

The Magnetic Field

Aims. We aim to study the magnetic field in solar spicules using high-resolution spectropolarimetric observations in the Ca II 8542 Å line obtained with the Swedish 1-m Solar Telescope. Methods. The equations that result from the application of the weak field approximation (WFA) to the radiative transfer equations were used to infer the line-of-sight (LOS) component of the magnetic field (BLOS). Two restrictive conditions were imposed on the Stokes I and V profiles at each pixel before they could be used in a Bayesian inversion to compute its BLOS. Results. The LOS magnetic field component was inferred in six data sets totalling 448 spectral scans in the Ca II 8542 Å line and containing both active region and quiet Sun areas, with values of hundreds of Gauss being abundantly inferred. There seems to be no difference, from a statistical point of view, between the magnetic field strength of spicules in the quiet Sun or near an active region. On the other hand, the BLOS distributions present smaller values on the disc than off-limb, a fact that can be explained by the effect of superposition on the chromosphere of on-disc structures. We show that on-disc pixels in which the BLOS is determined are possibly associated with spicular structures because these pixels are co-spatial with the magnetic field concentrations at the network boundaries and the sign of their BLOS agrees with that of the underlying photosphere. We find that spicules in the vicinity of a sunspot have a magnetic field polarity (i.e. north or south) equal to that of the sunspot. This paper also contains an analysis of the effect of off-limb overlapping structures on the observed Stokes I and V parameters and the BLOS obtained from the WFA. It is found that this value is equal to or smaller than the largest LOS magnetic field components of the two structures. In addition, using random BLOS, Doppler velocities, and line intensities of these two structures leads in ≃50% of the cases to Stokes I and V parameters that are unsuitable to be used with the WFA. Conclusions. Our results present a scarcity of LOS magnetic field components smaller than some 50 G, which must not be taken as evidence against the existence of these magnetic field strengths in spicules. This fact possibly arises as the consequence of signal superposition and noise in the data. We also suggest that the failure of previous works to infer the strong magnetic fields in spicules detected here is their coarser spatial and/or temporal resolution.

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Intensity contrast of solar plage as a function of magnetic flux at high spatial resolution

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833722 ◽

2019 ◽

Vol 621 ◽

pp. A78 ◽

Cited By ~ 2

Author(s):

F. Kahil ◽

T. L. Riethmüller ◽

S. K. Solanki

Keyword(s):

Magnetic Field ◽

Active Region ◽

Spatial Resolution ◽

High Spatial Resolution ◽

Disk Center ◽

Magnetic Element ◽

Quiet Sun ◽

Near Ultraviolet ◽

Magnetic Elements ◽

Intensity Contrast

Magnetic elements have an intensity contrast that depends on the type of region they are located in (for example quiet Sun, or active region plage). Observed values also depend on the spatial resolution of the data. Here we investigate the contrast-magnetic field dependence in active region plage observed near disk center with SUNRISE during its second flight in 2013. The wavelengths under study range from the visible at 525 nm to the near ultraviolet (NUV) at 300 nm and 397 nm. We use quasi-simultaneous spectropolarimetric and photometric data from the Imaging Magnetograph eXperiment (IMaX) and the Sunrise Filter Imager (SuFI), respectively. We find that in all wavelength bands, the contrast exhibits a qualitatively similar dependence on the line-of-sight magnetic field, BLOS, as found in the quiet Sun, with the exception of the continuum at 525 nm. There, the contrast of plage magnetic elements peaks for intermediate values of BLOS and decreases at higher field strengths. By comparison, the contrast of magnetic elements in the quiet Sun saturates at its maximum value at large BLOS. We find that the explanation of the turnover in contrast in terms of the effect of finite spatial resolution of the data is incorrect with the evidence provided by the high-spatial resolution SUNRISE data, as the plage magnetic elements are larger than the quiet Sun magnetic elements and are well-resolved. The turnover comes from the fact that the core pixels of these larger magnetic elements are darker than the quiet Sun. We find that plages reach lower contrast than the quiet Sun at disk center at wavelength bands formed deep in the photosphere, such as the visible continuum and the 300 nm band. This difference decreases with formation height and disappears in the Ca II H core, in agreement with empirical models of magnetic element atmospheres.

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Global Oscillations and Active Regions

Australian Journal of Physics ◽

10.1071/ph850839 ◽

1985 ◽

Vol 38 (6) ◽

pp. 839

Author(s):

CJ Durrant

Keyword(s):

Active Region ◽

Active Regions ◽

Solar Disc ◽

Velocity Variation ◽

Velocity Signal ◽

Velocity Modulation ◽

Quiet Sun ◽

Velocity Amplitude

We present further estimates of the amplitude of the modulation of the solar global velocity signal caused by the passage of active regions across the solar disc. Using measurements of the profile of the K I It 769�9 nm line in the quiet Sun and in plages we find a global velocity variation of ~ 2 m s - 1 during the transit of a typical active region of area 3300 millionths of the hemisphere. However, during the period in which a velocity amplitude of 6 m s - 1 was reported by Claverie et al. (1982), the sunspot areas were exceptionally large and we confirm Schroter's (1984) result that the combination of spot 'and plage contributions is sufficient to account for the observed signal. The velocity modulation is thus attributable to surface inhomogeneities, not to the structure of the solar core.

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Magnetic reconnection between an emerging active region and the quiet Sun

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316000168 ◽

2015 ◽

Vol 11 (S320) ◽

pp. 185-190

Author(s):

Bin Zhang ◽

Jun Zhang ◽

Shuhong Yang ◽

Ting Li ◽

Yuzong Zhang ◽

...

Keyword(s):

Active Region ◽

Magnetic Reconnection ◽

Extreme Ultraviolet ◽

Solar Dynamics Observatory ◽

Quiet Sun ◽

Quiet Region ◽

Released Energy ◽

Solar Dynamics ◽

Ultraviolet Observations

AbstractUsing the Solar Dynamics Observatory observations, we study the evolution of an emerging active region (EAR) and its reconnection with the quiet Sun. The EAR continuously interacts with the surrounding quiet region, and dark ribbons at the boundary of the EAR and the quiet Sun are observed. The extreme-ultraviolet observations show that the regions swept by the dark ribbons are brightened and the temperature increases. These results reveal that there exists an uninterrupted magnetic reconnection between the EAR and the quiet region and the released energy heats the corona of the quiet Sun. The dark ribbons are suggested to correspond to the interface of the reconnected fields and the undisturbed ones. The dark ribbon propagates outward, and this phenomenon is considered as a dark wave.

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Hinode EIS line widths in the quiet corona up to 1.5 R⊙

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834625 ◽

2019 ◽

Vol 631 ◽

pp. A163 ◽

Cited By ~ 2

Author(s):

G. Del Zanna ◽

G. R. Gupta ◽

H. E. Mason

Keyword(s):

Active Region ◽

Extreme Ultraviolet ◽

Alfven Waves ◽

Alfvén Waves ◽

Firm Conclusion ◽

Coronal Line ◽

Imaging Spectrometer ◽

Quiet Sun ◽

Line Widths

We present an analysis of several Hinode Extreme-ultraviolet Imaging Spectrometer (EIS) observations of coronal line widths in the quiet Sun, up to 1.5 R⊙ radial distances. Significant variations are found, which indicates no damping of Alfvén waves in the quiescent corona. However, the uncertainties in estimating the instrumental width mean that a firm conclusion cannot be reached. We present a discussion of various EIS instrumental issues and suggest that the strongest lines, from Fe XII at 193.5 Å and 195.1 Å, have anomalous instrumental widths. We also show how line widths in EIS are uncertain when the signal is low, and that the instrumental variation along the slit is also uncertain. We also find an anomalous decrease (up to 40%) in the intensities of these lines in many off-limb and active region observations, and provide evidence that this is due to opacity effects. We find that the most reliable measurements are obtained from the weaker lines.

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Oscillations observed in umbra, plage, quiet-Sun and the polarity inversion line of active region 11158 using Helioseismic Magnetic Imager/Solar Dynamics Observatory data

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2020.0175 ◽

2020 ◽

Vol 379 (2190) ◽

pp. 20200175 ◽

Cited By ~ 1

Author(s):

A. A. Norton ◽

R. B. Stutz ◽

B. T. Welsch

Keyword(s):

Active Region ◽

Wave Mode ◽

Phase Relations ◽

Doppler Velocity ◽

Solar Dynamics Observatory ◽

Spectra Analysis ◽

Polarity Inversion ◽

Quiet Sun ◽

Polarity Inversion Line ◽

Magnetic Oscillations

Using data from the Helioseismic Magnetic Imager, we report on the amplitudes and phase relations of oscillations in quiet-Sun, plage, umbra and the polarity inversion line (PIL) of an active region NOAA#11158. We employ Fourier, wavelet and cross-correlation spectra analysis. Waves with 5 min periods are observed in umbra, PIL and plage with common phase values of ϕ ( v , I ) = π /2, ϕ ( v , B los ) = −( π /2). In addition, ϕ ( I , B los ) = π in plage are observed. These phase values are consistent with slow standing or fast standing surface sausage wave modes. The line width variations, and their phase relations with intensity and magnetic oscillations, show different values within the plage and PIL regions, which may offer a way to further differentiate wave mode mechanics. Significant Doppler velocity oscillations are present along the PIL, meaning that plasma motion is perpendicular to the magnetic field lines, a signature of Alvènic waves. A time–distance diagram along a section of the PIL shows Eastward propagating Doppler oscillations converting into magnetic oscillations; the propagation speeds range between 2 and 6 km s −1 . Lastly, a 3 min wave is observed in select regions of the umbra in the magnetogram data. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

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