Magnetic Bright Points in the Quiet Sun (original) (raw)
Related papers
Preprint typeset using LATEX style emulateapj v. 11/10/09 MAGNETIC BRIGHT POINTS IN THE QUIET SUN
2010
We present a visual determination of the number of bright points (BPs) existing in the quiet Sun, which are structures though to trace intense kG magnetic concentrations. The measurement is based on a 0. ′′ 1 angular resolution G-band movie obtained with the Swedish Solar Telescope at the solar disk center. We find 0.97 BPs Mm −2 , which is a factor three larger than any previous estimate. It corresponds to 1.2 BPs per solar granule. Depending on the details of the segmentation, the BPs cover between 0.9 % and 2.2 % of the solar surface. Assuming their field strength to be 1.5 kG, the detected BPs contribute to the solar magnetic flux with an unsigned flux density between 13 G and 33 G. If network and inter-network regions are counted separately, they contain 2.2 BPs Mm −2 and 0.85 BPs Mm −2 , respectively.
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...
The Area Distribution of Solar Magnetic Bright Points
The Astrophysical Journal, 2010
Magnetic Bright Points (MBPs) are among the smallest observable objects on the solar photosphere. A combination of G-band observations and numerical simulations is used to determine their area distribution. An automatic detection algorithm, employing 1-dimensional intensity profiling, is utilized to identify these structures in the observed and simulated datasets. Both distributions peak at an area of ≈45000 km 2 , with a sharp decrease towards smaller areas. The distributions conform with lognormal statistics, which suggests that flux fragmentation dominates over flux convergence. Radiative magneto-convection simulations indicate an independence in the MBP area distribution for differing magnetic flux densities. The most commonly occurring bright point size corresponds to the typical width of intergranular lanes.
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.
Small-scale motions over concentrated magnetic regions of the quiet Sun
Solar Physics, 1987
We have used a 5.5 min time-sequence of spectra in the Fe I lines 25576 (magnetically insensitive),)~6301.5 and 26302.5 (magnetically sensitive) to study the association of concentrated magnetic regions and velocity in the quiet Sun. After the elimination of photospheric oscillations we found downflows of 100-300 m s ~, displaced by about 2" from the peaks of the magnetic field; this velocity is comparable to downflow velocity associated with the granulation and of the same order or smaller than the oscillation amplitude. Quasi-periodic time variations of the vertical component of the magnetic field up to +_ 40% were also found with a period near 250 s, close to the values found for the velocity field. Finally we report a possible association of intensity maxima at the line center with peaks of the oscillation amplitude.
A New View of the Magnetic Sun
Symposium - International Astronomical Union, 2003
Developments in instrumentation, numerical simulations, and theory are rapidly changing our view of solar magnetism. There are now observations that show magnetic field emerging on all convective scales. The emergence rate replaces the quiet Sun flux in less than 12 hours and even active region and sunspot fields are replaced in less than a month. There is evidence for local dynamo action suggesting that a bottom to a convection zone is not required for stellar magnetic activity. It is now recognized that 3D magnetic reconnection is fundamentally different from 2D. Time sequences of the one arc second spatial resolution TRACE images show that the temperature and density structure of the corona changes as fast as radiation and conduction allow. Because adjacent loops are observed in a range of temperatures that span at least 30 000 to 2 500 000 K, there is a inter mixture of temperatures regimes throughout the corona. Consequently, there is no line of sight through the corona that ca...
The mean magnetic field of the Sun: Observations at Stanford
Solar Physics, 1977
A solar telescope has been built at Stanford University to study the organization and evolution of large-scale solar magnetic fields and velocities. The observations are made using a Babcock-type magnetograph which is connected to a 22.9 m vertical Littrow spectrograph. Sun-as-a-star integrated light measurements of the mean solar magnetic field have been made daily since May 1975. The typical mean field magnitude has been about 0.15 G with typical measurement error less than 0.05 G. The mean field polarity pattern is essentially identical to the interplanetary magnetic field sector structure (see near the Earth with a 4 day lag). The differences in the observed structures can be understood in terms of a ‘warped current sheet’ model.
AIP Conference Proceedings, 2003
The seemingly un-magnetized part of the solar surface is not really un-magnetized. It is occupied by magnetic structures producing low polarization which, therefore, escape detection in traditional measurements. Since most of the solar surface belongs to this category, the quiet Sun magnetic fields can easily carry most of the magnetic flux and energy existing in the photosphere at any given time. Consequently, they are a potentially important ingredient of the solar magnetism. Most of the physical properties of the quiet Sun are still uncertain (distribution of field strengths, area coverage, influence on higher atmospheric layers, etc.).It is clear, however, that the topology of the field is complex, with field lines of very different properties coexisting in each resolution element. This fact hampers the detection of the quiet Sun magnetic fields. I argue that the best present measurements detect, at most, 30 % of the existing magnetic flux. Then the quiet Sun contains at least as much magnetic flux as all active regions and the network during the solar maximum.