scholarly journals Spectrometer-Based Magnetographs

1993 ◽  
Vol 141 ◽  
pp. 156-165
Author(s):  
Harrison P. Jones
Keyword(s):  
Fourier Transform ◽  
Velocity Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Spectral Range ◽  
Equivalent Width ◽  
Active Regions ◽  
Continuum Intensity ◽  
Array Detectors ◽  
Line Depth

AbstractThe techniques and instrumentation for inferring magnetic fields using a spectrometer or spectrograph rather than a narrowband filter are reviewed. With array detectors and/or Fourier transform spectroscopy, the polarimetric data is acquired over the relevant spectral range strictly simultaneously with no possibility of spatial misregistration. Several recent examples of spectrometer-based magnetographs are discussed and compared, and new observations from the NASA/NSO Spectromagnetograph of magnetic flux, velocity field, continuum intensity, equivalent width, and line depth in active regions and the whole sun are shown.

Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

2000 ◽  
Vol 179 ◽  
pp. 263-264
Author(s):  
K. Sundara Raman ◽  
K. B. Ramesh ◽  
R. Selvendran ◽  
P. S. M. Aleem ◽  
K. M. Hiremath
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Ultra Violet ◽  
Active Regions ◽  
Morphological Properties ◽  
Energy Storage And Conversion ◽  
The Sun ◽  
X Rays ◽  
The Magnetic Field

Extended AbstractWe have examined the morphological properties of a sigmoid associated with an SXR (soft X-ray) flare. The sigmoid is cospatial with the EUV (extreme ultra violet) images and in the optical part lies along an S-shaped Hαfilament. The photoheliogram shows flux emergence within an existingδtype sunspot which has caused the rotation of the umbrae giving rise to the sigmoidal brightening.It is now widely accepted that flares derive their energy from the magnetic fields of the active regions and coronal levels are considered to be the flare sites. But still a satisfactory understanding of the flare processes has not been achieved because of the difficulties encountered to predict and estimate the probability of flare eruptions. The convection flows and vortices below the photosphere transport and concentrate magnetic field, which subsequently appear as active regions in the photosphere (Rust & Kumar 1994 and the references therein). Successive emergence of magnetic flux, twist the field, creating flare productive magnetic shear and has been studied by many authors (Sundara Ramanet al.1998 and the references therein). Hence, it is considered that the flare is powered by the energy stored in the twisted magnetic flux tubes (Kurokawa 1996 and the references therein). Rust & Kumar (1996) named the S-shaped bright coronal loops that appear in soft X-rays as ‘Sigmoids’ and concluded that this S-shaped distortion is due to the twist developed in the magnetic field lines. These transient sigmoidal features tell a great deal about unstable coronal magnetic fields, as these regions are more likely to be eruptive (Canfieldet al.1999). As the magnetic fields of the active regions are deep rooted in the Sun, the twist developed in the subphotospheric flux tube penetrates the photosphere and extends in to the corona. Thus, it is essentially favourable for the subphotospheric twist to unwind the twist and transmit it through the photosphere to the corona. Therefore, it becomes essential to make complete observational descriptions of a flare from the magnetic field changes that are taking place in different atmospheric levels of the Sun, to pin down the energy storage and conversion process that trigger the flare phenomena.

scholarly journals Observations of magnetic and kinetic helicity proxies

2012 ◽  
Vol 8 (S294) ◽  
pp. 13-24
Author(s):  
Hongqi Zhang
Keyword(s):  
Magnetic Field ◽  
Velocity Field ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
Active Regions ◽  
Solar Dynamo ◽  
Magnetic Helicity ◽  
Vector Magnetograms ◽  
Topological Configuration ◽  
The Relationship

AbstractThe helicity is important to present the basic topological configuration of magnetic field in solar atmosphere. The distribution of magnetic helicity in solar atmosphere is presented by means of the observational (vector) magnetograms. As the kinetic helicity in the solar subatmosphere can be inferred from the velocity field based on the technique of the helioseismology and used to compare with the magnetic helicity in the solar atmosphere, the observational helicities provide the important chance for the confirmation on the generation of magnetic fields in the subatmosphere and solar dynamo models also. In this paper, we present the observational magnetic and kinetic helicity in solar active regions and corresponding questions, except the relationship with solar eruptive phenomena.

scholarly journals Irradiance Models Based on Solar Magnetic Fields

1994 ◽  
Vol 143 ◽  
pp. 217-225 ◽  
Author(s):  
Karen L. Harvey
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Coronal Holes ◽  
Active Regions ◽  
Spectral Irradiance ◽  
Solar Magnetic Fields ◽  
Quiet Sun ◽  
Possible Cause

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.

scholarly journals Small-Scale Magnetic Features Observed in the Photosphere

1990 ◽  
Vol 138 ◽  
pp. 129-146 ◽  
Author(s):  
Sara F. Martin
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Active Regions ◽  
Line Of Sight ◽  
Small Scale ◽  
Quiet Sun ◽  
Magnetic Features

Small-scale solar features identifiable on the quiet sun in magnetograms of the line-of-sight component consist of network, intranetwork, ephemeral region magnetic fields, and the elementary bipoles of ephemeral active regions. Network fields are frequently observed to split into smaller fragments and equally often, small fragments are observed to merge or coalesce into larger clumps; this splitting and merging is generally confined to the borders and vertices of the convection cells known as supergranules. Intranetwork magnetic fields originate near the centers of the supergranule convection cells and appear to increase in magnetic flux as they flow in approximate radial patterns towards the boundaries of the cells.

scholarly journals Investigation of Spatially Unresolved Magnetic Field Outside Sunspots Using Hinode/SOT Observations

2016 ◽  
Vol 12 (S325) ◽  
pp. 59-62
Author(s):  
Olga Botygina ◽  
Mykola Gordovskyy ◽  
Vsevolod Lozitsky
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Zeeman Effect ◽  
Active Regions ◽  
Line Ratio ◽  
Optical Telescope ◽  
Flux Tubes ◽  
Magnetic Flux Tubes ◽  
The Magnetic Field

AbstractThe structure of photospheric magnetic fields outside sunspots is investigated in three active regions using Hinode/Solar Optical Telescope(SOT) observations. We analyze Zeeman effect in FeI 6301.5 and FeI 6302.5 lines and determine the observed magnetic field value Beff for each of them. We find that the line ratio Beff(6301)/Beff(6302) is close to 1.3 in the range Beff < 0.2 kG, and close to 1.0 for 0.8 kG < Beff < 1.2 kG. We find that the observed magnetic field is formed by flux tubes with the magnetic field strengths 1.3 − 2.3 kG even in places with weak observed magnetic field fluxes. We also estimate the diameters of smallest magnetic flux tubes to be 15 − 20 km.

Structure within a Magnetic Flux Tube

1978 ◽  
Vol 3 (3) ◽  
pp. 225-226
Author(s):  
P. R. Wilson
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Observational Studies ◽  
Active Regions ◽  
Background Field ◽  
Magnetic Flux Tube ◽  
Small Scale ◽  
Solar Magnetic Fields ◽  
Intense Fields ◽  
Initial Discovery

Since their initial discovery by Hale, the nature of solar magnetic fields has presented us with a number of problems. At one time it was thought that the field consisted of a weak background dipole field of order 1-2 G on which was superimposed the considerably more intense fields associated with active regions and sunspots. However, more recent observational studies by Harvey, Frasier, Stenflo and others have suggested that 90% of the background field appears in the form of intense small-scale fields with intensities of order 103 gauss or greater and which have remarkably similar properties whether they occur in active or quiet regions. In particular, the field intensity appears independent of the total amount of flux present but the appearance of the structure depends critically on the total flux.

Possible Amount of Magnetic Flux Reconnected Through Quiescent Prominences Outside the Active Regions

1979 ◽  
Vol 44 ◽  
pp. 189-191
Author(s):  
M.H. Gokhale ◽  
K.R. Sivaraman
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Working Group ◽  
Large Scale ◽  
Active Regions ◽  
Current Sheets ◽  
Satisfactory Model ◽  
Almost All ◽  
Group 1

Quiescent prominences are known to occur invariably above the neutral lines in the large scale photospheric fields. This suggests that such prominences may be coronal current sheets across which the magnetic fields reconnect (cf. e.g. Raadu and Kuperus, 1973). In the absence of any satisfactory model for quiescent prominences (cf. Report of Working Group 1 in this Colloquium), the reconnection hypothesis remains as yet unsettled. However, if it is true, we have here an evidence to show that the quiescent prominences outside the active regions might account for the reconnection of almost all the photospheric magnetic flux emerging in the active regions as required by the theories of the 11-yr cycle of activity (e.g. Babcock, 1961).

scholarly journals Magnetic field evolution of active regions and sunspots in connection with chromospheric and coronal activities

2010 ◽  
Vol 6 (S273) ◽  
pp. 157-163
Author(s):  
Toshifumi Shimizu
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Active Regions ◽  
Vector Magnetic Field ◽  
Optical Telescope ◽  
Magnetic Field Data ◽  
Flux Tubes ◽  
X Ray ◽  
Magnetic Flux Tubes

AbstractCa II H imaging observations by the Hinode Solar Optical Telescope (SOT) have revealed that the chromosphere is extremely dynamic and that ejections and jets are well observed in moat region around sunspots. X-ray and EUV observations show frequent occurrence of microflaring activities around sunspots; small emerging flux or moving magnetic features approaching opposite pre-existing magnetic flux can be identified on the footpoints for half of microflares studied, while no encounters of opposite polarities are observed at footpoints for the others even with SOT high spatial magnetorams (Kano et al. 2010). Another observations tell the involvement of twisted magnetic fields in the microflares accompanied by no polarity encounters at the footpoints. Some type of sunspot light bridges shows recurrent occurrence of chromospheric ejections, and photospheric vector magnetic field data suggests that twsited magnetic flux tubes lying along light bridge play vital roles in producing such ejections (Shimizu et al. 2009). This presentation reviewed observational findings from these studies. We will need to understand the 3D configuration of magnetic fields for better understanding of activity triggers in the solar atmosphere.

scholarly journals Spectral investigations of magnetic fields and thermodynamic conditions in active regions on the Sun

2019 ◽  
pp. 15-22
Author(s):  
V. Lozitsky
Keyword(s):  
Magnetic Fields ◽  
Solar Flare ◽  
Magnetic Flux ◽  
Active Regions ◽  
Doppler Velocity ◽  
The Sun ◽  
Strong Magnetic Fields ◽  
Flux Tubes ◽  
Thermodynamic Conditions ◽  
Mixed Polarity

The main results of studies of magnetic fields and thermodynamic conditions in active regions in the Sun obtained at the Astronomical Observatory of the Taras Shevchenko National University of Kyiv (AO KNU) during the last 10 years (2010–2019) are presented. The true diameter of the extremely small(spatially unresolved) magnetic flux tubes was estimated on a base of data from Hinode Space Observatory; this diameter was found to be within the range of 15–20 km, which is much smaller than the spatial resolution limit of the largest solar telescopes to date (≈ 60 km). According to the observations made at AO KNU, it was shown that there are three types of magnetic fields in a solar faculae: strong (kilogauss range) fields in small-scale flux tubes, areas of weak and moderate background fields of regular polarity, and areas of sub-telescopic fields of mixed polarity. The magnetic flux of mixed polarity exceeds the absolute flux of the entire field of regular polarity by at least 2 times. In the sunspot umbra observed at GST of AO KNU and ATsU-5 of GAO NASU, thin spectral effects of Zeeman splitting were found, which indicate presence of very strong magnetic fields at least of 5,8 kG. The polarity of the magnetic field in sub-telescopic structures with such very strong fields is found to be the same as in the background field, and the Doppler velocity is about 2 km/s (plasma lifting). Super- strong magnetic fields in the range of 5–5,7 kG were also detected from observations of the Big Bear Observatory (BBSO), USA. A unique observational material also obtained on AO KNU concerning the area of a seismic source of extremely powerful solar flare on October 28, 2003 of X17.2 / 4B class was analyzed. This solar flare had a Balmer decrement with a record intensity ratio I (Hβ) / I (Hα) = 1,68 of the Hβ and Hα lines, which is unprecedented for all flares observed. In this flare, indications of the existence of particularly strong magnetic fields in the range of several tens of kilogauss were found. The semi-empirical model of this flare has an interesting feature, namely three discrete layers with high plasma concentration and temperature, including a very thick and thin layer in the chromosphere with the following parameters: hydrogen concentration nH = 1018 cm–3, thickness Δh = 3–5 km and height h ≈ 1200 km above the level of the photosphere. In active solar prominences, rather strong magnetic fields (up to 4 kG) were detected at altitudes of 3–14 Mm. The modeling of spectral line profiles within the two-component model showed that the true magnitude of local magnetic fields can be even greater by at least 3 times. A theoretical MHD model is proposed, according to which such high strengths occur in force-free magnetic ropes with a characteristic scale of 300 km.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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