Theory of the Solar 22-Year Cycle

1971 ◽  
Vol 2 (1) ◽  
pp. 7-10 ◽  
Author(s):  
J. H. Piddington
Keyword(s):  
Magnetic Fields ◽  
Solar Surface ◽  
Velocity Fields ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Radio Bursts ◽  
X Rays ◽  
Plasma Velocity ◽  
Full Understanding ◽  
Satisfactory Theory

If there were no solar magnetic fields, then the most active feature observable on the Sun would be the hydrodynamic convection. There would be no sunspots, flares, prominences, plage, spicules, and no copious emissions of X-rays, energetic particles or radio bursts. These effects are all due to the presence of a changing pattern of magnetic fields which repeats every 22 years. While observations of electromagnetic phenomena are limited to the solar surface and atmosphere, a full understanding of these effects must include a satisfactory theory of the solar cycle and of the fields which evolve beneath the surface as a result of plasma velocity fields.

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.

The Interpretation of Line Profiles

1977 ◽  
Vol 36 ◽  
pp. 191-215
Author(s):  
G.B. Rybicki
Keyword(s):  
Magnetic Fields ◽  
Atomic Physics ◽  
Velocity Fields ◽  
Spectral Lines ◽  
Inhomogeneous Structure ◽  
The Sun ◽  
Line Profiles ◽  
Physical Phenomena

Observations of the shapes and intensities of spectral lines provide a bounty of information about the outer layers of the sun. In order to utilize this information, however, one is faced with a seemingly monumental task. The sun’s chromosphere and corona are extremely complex, and the underlying physical phenomena are far from being understood. Velocity fields, magnetic fields, Inhomogeneous structure, hydromagnetic phenomena – these are some of the complications that must be faced. Other uncertainties involve the atomic physics upon which all of the deductions depend.

scholarly journals Small Scale Solar Magnetic Fields: Theory

1977 ◽  
Vol 4 (2) ◽  
pp. 241-250 ◽  
Author(s):  
N. O. Weiss
Keyword(s):  
Magnetic Fields ◽  
Field Strength ◽  
Solar Physics ◽  
Small Scale ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Solar Granulation ◽  
The Past ◽  
Maximum Field Strength ◽  
Maximum Field

One of the most exciting developments in solar physics over the past eight years has been the success of ground based observers in resolving features with a scale smaller than the solar granulation. In particular, they have demonstrated the existence of intense magnetic fields, with strengths of up to about 1600G. Harvey (1976) has just given an excellent summary of these results.In solar physics, theory generally follows observations. Inter-granular magnetic fields had indeed been expected but their magnitude came as a surprise. Some problems have been discussed in previous reviews (Schmidt, 1968, 1974; Weiss, 1969; Parker, 1976d; Stenflo, 1976) and the new observations have stimulated a flurry of theoretical papers. This review will be limited to the principal problems raised by these filamentary magnetic fields. I shall discuss the interaction of magnetic fields with convection in the sun and attempt to answer such questions as: what is the nature of the equilibrium in a flux tube? how are the fields contained? what determines their stability? how are such strong fields formed and maintained? and what limits the maximum field strength?

scholarly journals Small-Scale Solar Magnetic Fields

1976 ◽  
Vol 71 ◽  
pp. 69-99 ◽  
Author(s):  
J. O. Stenflo
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Solar Surface ◽  
Life Time ◽  
Wave Number ◽  
Small Scale ◽  
Solar Magnetic Fields ◽  
Field Amplification ◽  
Wave Numbers ◽  
Diffuse Form

The observed properties of small-scale solar magnetic fields are reviewed. Most of the magnetic flux in the photosphere is in the form of strong fields of about 100–200 mT (1–2 kG), which have remarkably similar properties regardless of whether they occur in active or quiet regions. These fields are associated with strong atmospheric heating. Flux concentrations decay at a rate of about 107 Wb s-1, independent of the amount of flux in the decaying structure. The decay occurs by smaller flux fragments breaking loose from the larger ones, i.e. a transfer of magnetic flux from smaller to larger Fourier wave numbers, into the wave-number regime where ohmic diffusion becomes significant. This takes place in a time-scale much shorter than the length of the solar cycle.The field amplification occurs mainly below the solar surface, since very little magnetic flux appears in diffuse form in the photosphere, and the life-time of the smallest flux elements is very short. The observations further suggest that most of the magnetic flux in quiet regions is supplied directly from below the solar surface rather than being the result of turbulent diffusion of active-region magnetic fields.

scholarly journals Progress in the Measurement of Solar Magnetic Fields

1993 ◽  
Vol 141 ◽  
pp. 149-155 ◽  
Author(s):  
Guoxiang Ai
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
White Light ◽  
Historical Development ◽  
Solar Magnetic Field ◽  
Solar Physics ◽  
Monochromatic Light ◽  
Velocity Fields ◽  
Solar Magnetic Fields ◽  
Optical Instruments

AbstractThe historical development of optical instruments for solar physics is outlined, from white light to unpolarized and polarized monochromatic light, to Stokes profiles and simultaneous fields of view, from points to lines, plane to cube. An evolutionary series and classificaton of instruments for the solar magnetic field is described. As a next step the 2-D real time polarizing spectrograph has been proposed. The planned instruments in China for measurements of solar magnetic and velocity fields are briefly introduced.

RSFP CONSTRAINTS ON THE TWISTING PROFILES OF SOLAR MAGNETIC FIELDS FROM THE SOLAR NEUTRINO DATA

1998 ◽  
Vol 13 (40) ◽  
pp. 3201-3211 ◽  
Author(s):  
UMESH CHANDRA PANDEY ◽  
B. C. CHAUHAN ◽  
S. DEV
Keyword(s):  
Magnetic Fields ◽  
Solar Neutrino ◽  
Convective Zone ◽  
The Sun ◽  
Solar Magnetic Fields

Constraints on the possible twisting profiles of the magnetic fields in the convective zone of the Sun have been derived within the framework of the Resonant Spin Flavor Precession (RSFP) scenario in the light of solar neutrino observations.

scholarly journals Analog Video Magnetograms in Real Time

1971 ◽  
Vol 43 ◽  
pp. 76-83 ◽  
Author(s):  
R. C. Smithson ◽  
R. B. Leighton
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Magnetic Field ◽  
Solar Spectrum ◽  
Zeeman Splitting ◽  
The Other ◽  
Line Of Sight ◽  
Zero Field ◽  
The Sun ◽  
Solar Magnetic Fields

For many years solar magnetic fields have been measured by a variety of techniques, all of which exploit the Zeeman splitting of lines in the solar spectrum. One of these techniques (Leighton, 1959) involves a photographic subtraction of two monochromatic images to produce a picture of the Sun in which the line-of-sight component of the solar magnetic field appears as various shades of gray. In a magnetogram made by this method, zero field strength appears as neutral gray, while magnetic fields of one polarity or the other appear as lighter or darker areas, respectively. Figure 1 shows such a magnetogram.

scholarly journals Correlations between brightness fields and magnetic fields on the Sun

1968 ◽  
Vol 35 ◽  
pp. 161-173
Author(s):  
G. A. Chapman ◽  
N. R. Sheeley
Keyword(s):  
Magnetic Fields ◽  
Solar Surface ◽  
The Sun ◽  
Photographic Technique ◽  
Preliminary Results ◽  
Chromospheric Network

In places on the solar surface where longitudinal magnetic fields are detectable using Leighton's photographic technique, spectroheliograms taken in the cores of many Fraunhofer lines show a bright photospheric network similar to, but with finer structure than, the familiar chromospheric network visible on Ca+ K232 spectroheliograms. This paper describes preliminary results of a study of the relation between the photospheric network and its associated magnetic fields.

scholarly journals Evolution of Large and Small Scale Magnetic Fields in the Sun

1991 ◽  
Vol 130 ◽  
pp. 218-222
Author(s):  
Peter A. Fox ◽  
Michael L. Theobald ◽  
Sabatino Sofia
Keyword(s):  
Numerical Simulation ◽  
Magnetic Fields ◽  
Time Dependence ◽  
Large Scale ◽  
Sunspot Cycle ◽  
Small Scale ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Magnetic Resistivity ◽  
Statistical Evolution

AbstractThis paper will discuss issues relating to the detailed numerical simulation of solar magnetic fields, those on the small scale which are directly observable on the surface, and those on larger scales whose properties must be deduced indirectly from phenomena such as the sunspot cycle. Results of simulations using the ADISM technique will be presented to demonstrate the importance of the treatment of Alfvén waves, the boundary conditions, and the statistical evolution of small scale convection with magnetic fields. To study the large scale fields and their time dependence, the magnetic resistivity plays an important role; its use will be discussed in the paper.

scholarly journals Comments on X-rays emitted by the sun

1965 ◽  
Vol 23 ◽  
pp. 57-59
Author(s):  
John C. Lindsay
Keyword(s):  
Solar Observatory ◽  
The Sun ◽  
Radio Bursts ◽  
X Rays ◽  
X Ray ◽  
Quiet Sun ◽  
Upper Limit

Observations from the first Orbiting Solar Observatory have set an upper limit of 3.40 ± 0.95 photons/cm2.s for the 20–100 keV X-ray flux from the “quiet” Sun. Eight impulsive and short-lived 20–100 keV X-ray bursts were observed which were associated with optical flares and cm radio bursts. The 2–8 Å X-ray flux from the “quiet” Sun was observed to be associated with plage groups on the Sun. The intensity for this 2–8 Å X-radiation was found to be quite variable, changes of 5% being observed almost hourly.

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