On the intensity contrast of solar photospheric faculae and network elements (original) (raw)
Related papers
The Astrophysical Journal, 2019
Solar irradiance models indicate that irradiance variations are dominated by changes in the disk-coverage of magnetic structures, whose brightness is thought to be determined by their size and average magnetic flux density. Recent results suggest that the brightness of small-scale magnetic structures also depends on the mean magnetic flux of the extended region surrounding them due to reduced convective vigor. Low spatial resolution, however, may limit the ability to distinguish the role of magnetic structure size distributions from that of the mean magnetic flux. Using high-resolution 3D MHD simulations, we investigate the brightness of magnetic structures embedded in regions characterized by different mean magnetic flux. In agreement with previous results, we find reduced brightness with increasing mean magnetic flux when comparing the pixel-by-pixel continuum brightness versus magnetic field strength. Evaluating equivalently sized magnetic structures, however, we find no significant dependence of the magnetic structure brightness on the mean magnetic flux of the region in which they are embedded. Rather, we find that simulations with larger mean magnetic flux generate larger, and therefore darker, magnetic structures whose contributions result in an overall darkening of the region. The differences in magnetic structure size distributions alone can explain the reduced brightness of regions with larger mean magnetic flux. This implies that, for the range of mean magnetic flux of the simulations, convective suppression plays at most a secondary role in determining radiative output of magnetized regions. Quantifying the role of convective transport over a wider range of mean magnetic flux is the subject of the second paper in this series.
The Distribution of the Quiet Sun Photospheric Magnetic Flux
Bulletin of the Astronomical Society of India
A gradient-based tessellating algorithm is used to study the magnetic field structure of the quiet Sun photosphere using SoRO full disk magnetograms. We find that the field is not uniformly distributed, but parcelled into flux concentrations. Both the flux and size of the concentrations are found to be described by broad, asymmetric distribution functions. Their mean absolute flux and size are found to be about 1.4 x 10 18 m:x: and 6.1 Mm for both polarities in unsmoothed magnetogra.ms at Ii gauss threshold. These values represent a. weighted average for both network-and intra.network magnetic fields, since the present method cannot currently distinguish between the two regions. Both flux and size distributions become more symmetric and less peaked in response to smoothing of images. Extrapolating this trend to sub-resolution seale, we note a linear decrease in size but a rapid increase in the mean absolute field strength, with asymptotic values of about 400 km and 50 gauss. This exercise shows that the true field strengths of quiet magnetic elements are higher and their size smaller than usua.lly inferred from observa.tions. This is because observation of mixed polarity regions under finite resolution causes the observed flux to be smeared out and apparently modified. Therefore, this flux cannot be interpreted independently of the geometric structure and flux distribution of the concentrations.
2017
Magnetic elements of the solar surface are studied (using the 6173 Å Fe i line) in magnetograms recorded with the high-resolution Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI). To extract some statistical and physical properties of these elements (e.g. filling factors, magnetic flux, size, and lifetimes), we employed the region-based method called Yet Another Feature Tracking Algorithm (YAFTA). An area of 400″×400″$400^{\prime\prime}\times400^{\prime\prime}$ was selected to investigate the magnetic characteristics in 2011. The correlation coefficient between filling factors of negative and positive polarities is 0.51. A broken power-law fit was applied to the frequency distribution of size and flux. Exponents of the power-law distributions for sizes smaller and greater than 16arcsec2$16~\mbox{arcsec}^{2}$ were found to be −2.24 and −4.04, respectively. The exponents of power-law distributions for fluxes lower and greater than 2.63×1019Mx$2.63\times 10^{19}~...
An atlas of photospheric magnetic field observations and computed coronal magnetic fields: 1976?1985
Solar Physics, 1986
Daily magnetogram observations of the large-scale photospheric magnetic field have been made at the John M. Wilcox Solar Observatory at Stanford since May of 1976' These measurements provide a homogeneous record of the changing solar field through most of Solar Cycle 21. Using the photospheric data, the configuration of the coronal and heliospheric fields can be calculated using a Potential Field-Source Surface model. This provides a 3,dimensional picture of the heliospheric field evolution during the solar cycle. In this note we announce the publication of UAG Report #94, an Atlas containing the complete set of synoptic charts of the measured photospheric magnetic field, the computed field at the source surface, and the coefficients of the multipole expansion of the coronal field. The general underlying structures of the solar and heliospheric fields, which determine the environment for solar-terrestrial relations and provide the context within which solar activity related events occur, can be approximated from these data.
Magnetic Field Strengths and Structures from Radio Observations of Solar Active Regions
Chinese Journal of Astronomy and Astrophysics, 2002
Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76 cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggests that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field.
2021
Here, we analyzed magnetic elements of the solar active regions (ARs) observed in the line-of-sight magnetograms (the 6173 Å Fe I line) recorded with the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI). The Yet Another Feature Tracking Algorithm (YAFTA) was employed to extract the statistical properties of these features (e.g. filling factor, magnetic flux, and lifetime) within the areas of 180′′ × 180′′ inside the flaring AR (NOAA 12443) and the non-flaring AR (NOAA 12446) for 3 to 5 November 2015 and for 4 to 6 November 2015, respectively. The mean filling factor of polarities was obtained to be about 0.49 for the flaring AR; this value was 0.08 for the non-flaring AR. Time series of the filling factors of the negative and positive polarities for the flaring AR showed anti-correlation (with the Pearson value of -0.80); while for the non-flaring AR, there was the strong positive correlation (with the Pearson value of 0.95). A power-law function was fitted to...
Observational evidence for two-component distributions describing solar magnetic bright points
Astronomy & Astrophysics
Context.High-resolution observations of the solar photosphere reveal the presence of fine structures, in particular the so-called Magnetic Bright Points (MBPs), which are small-scale features associated with strong magnetic field regions of the order of kilogauss (kG). It is especially relevant to study these magnetic elements, which are extensively detected in all moments during the solar cycle, in order to establish their contribution to the behavior of the solar atmosphere, and ultimately a plausible role within the coronal heating problem.Aims.Characterisation of size and velocity distributions of MBPs in the solar photosphere in two different datasets of quiet Sun images acquired with high-resolution solar instruments i.e. Solar Optical Telescope SOT/Hinode and the High-resolution Fast Imager HiFI/GREGOR, in theG-band (4308 Å).Methods.In order to detect the MBPs, an automatic segmentation and identification algorithm is used. Next, the identified features were tracked to measur...
Solar Physics, 1968
Several improvements have been made t o the M t. Wilson Observatory s o l a r magnetograph, including changes t o t h e guider, the Doppler compensator, and the d a t a handling system. The improved magnetograph has been used f o r a new t m e of s o l a r observation consisting of several hundred scans back and f o r t h along a s t r a i g h t l i n e of length 3/4 Ro perpendicular t o c e n t r a l meridian. The d a t a reduction, which i s done e n t i r e l y with a computer, eliminates those e f f e c t s which have t h e i r o r i g i n i n t h e earth-sun geometry. The s p a t i a l and temporal p r o p e r t i e s o f the 5-minute o s c i l l a t i o n s are discussed.
Astronomy & Astrophysics
Context. The emission of the upper atmosphere of the Sun is closely related to magnetic field concentrations at the solar surface. Aims. It is well established that this relation between chromospheric emission and magnetic field is nonlinear. Here we investigate systematically how this relation, characterised by the exponent of a power-law fit, changes through the atmosphere, from the upper photosphere through the temperature minimum region and chromosphere to the transition region. Methods. We used spectral maps from the Interface Region Imaging Spectrograph (IRIS) covering Mg II and its wings, C II, and Si IV together with magnetograms and UV continuum images from the Solar Dynamics Observatory. After a careful alignment of the data we performed a power-law fit for the relation between each pair of observables and determine the power-law index (or exponent) for these. This was done for different spatial resolutions and different features on the Sun. Results. While the correlation ...
Astronomy & Astrophysics, 2010
Context. The design of modern instruments does not only imply thorough studies of instrumental effects but also a good understanding of the scientific analysis planned for the data. Aims. We investigate the reliability of Milne-Eddington (ME) inversions of high-resolution magnetograph measurements such as those to be obtained with the Imaging Magnetograph eXperiment (IMaX) aboard the Sunrise balloon. We also provide arguments to choose either Fe i 525.02 or 525.06 nm as the most suitable line for IMaX. Methods. We reproduce an IMaX observation using magnetoconvection simulations of the quiet Sun and synthesizing the four Stokes profiles emerging from them. The profiles are degraded by spatial and spectral resolution, noise, and limited wavelength sampling, just as real IMaX measurements. We invert these data and estimate the uncertainties in the retrieved physical parameters caused by the ME approximation and the spectral sampling. Results. It is possible to infer the magnetic field strength, inclination, azimuth, and line-of-sight velocity from standard IMaX measurements (4 Stokes parameters, 5 wavelength points, and a signal-to-noise ratio of 1000) applying ME inversions to any of the Fe i lines at 525 nm. We also find that telescope diffraction has important effects on the spectra coming from very high resolution observations of inhomogeneous atmospheres. Diffration reduces the amplitude of the polarization signals and changes the asymmetry of the Stokes profiles. Conclusions. The two Fe i lines at 525 nm meet the scientific requirements of IMaX, but Fe i 525.02 nm is to be preferred because it leads to smaller uncertainties in the retrieved parameters and offers a better detectability of the weakest (linear) polarization signals prevailing in the quiet Sun.