Stability of bipolarons in the presence of a magnetic field

1997 ◽  
Vol 104 (4) ◽  
pp. 605-612 ◽  
Author(s):  
J.T. Devreese ◽  
F. Brosens
Keyword(s):  
Magnetic Field

Magnetic-field strengths from optical polarization data

1967 ◽  
Vol 31 ◽  
pp. 381-383
Author(s):  
J. M. Greenberg
Keyword(s):  
Magnetic Field ◽  
Optical Polarization ◽  
Polarization Data ◽  
Term Model ◽  
Source Of Information ◽  
Field Strengths

Van de Hulst (Paper 64, Table 1) has marked optical polarization as a questionable or marginal source of information concerning magnetic field strengths. Rather than arguing about this–I should rate this method asq+-, or quarrelling about the term ‘model-sensitive results’, I wish to stress the historical point that as recently as two years ago there were still some who questioned that optical polarization was definitely due to magnetically-oriented interstellar particles.

Observing the galactic magnetic field

1967 ◽  
Vol 31 ◽  
pp. 375-380
Author(s):  
H. C. van de Hulst
Keyword(s):  
Magnetic Field ◽  
Fair Agreement ◽  
Solar Neighbourhood ◽  
Galactic Magnetic Field ◽  
The Magnetic Field

Various methods of observing the galactic magnetic field are reviewed, and their results summarized. There is fair agreement about the direction of the magnetic field in the solar neighbourhood:l= 50° to 80°; the strength of the field in the disk is of the order of 10-5gauss.

Structure in the radiation of the galactic disk

1967 ◽  
Vol 31 ◽  
pp. 355-356
Author(s):  
R. D. Davies
Keyword(s):  
Magnetic Field ◽  
Galactic Disk ◽  
Galactic Magnetic Field ◽  
Measured Polarization

Observations at various frequencies between 136 and 1400 MHz indicate a considerable amount of structure in the galactic disk. This result appears consistent both with measured polarization percentages and with considerations of the strength of the galactic magnetic field.

Calculated Coronal Magnetic Fields and Their Comparison with the Coronal Structures as Observed during Five Solar Eclipses

1994 ◽  
Vol 144 ◽  
pp. 559-564
Author(s):  
P. Ambrož ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Coronal Magnetic Field ◽  
Coronal Magnetic Fields ◽  
Solar Eclipses ◽  
Coronal Structures

AbstractWe were successful in observing the solar corona during five solar eclipses (1973-1991). For the eclipse days the coronal magnetic field was calculated by extrapolation from the photosphere. Comparison of the observed and calculated coronal structures is carried out and some peculiarities of this comparison, related to the different phases of the solar cycle, are presented.

Faint Hα Emission in the Corona and Its Relation to the Prominences

1994 ◽  
Vol 144 ◽  
pp. 339-342
Author(s):  
V. N. Dermendjiev ◽  
Z. Mouradian ◽  
J.- L. Leroy ◽  
P. Duchlev
Keyword(s):  
Magnetic Field ◽  
Solar Corona ◽  
Essential Role ◽  
Hα Emission

AbstractThe relation between episodically observed in the solar corona faint Hαemission structures and the long lived prominences was studied. Particular consideration was given for cases in which the corresponding prominences had undergone DB process. An MHD interpretation of the phenomenon “emissions froides” (cool emission) is proposed in which an essential role plays the prominence supporting magnetic field.

Evolution of Large-Scale Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 29-33
Author(s):  
P. Ambrož
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
Source Surface ◽  
Solar Cycles ◽  
Characteristic Relationship ◽  
The Magnetic Field ◽  
Coronal Structures

AbstractThe large-scale coronal structures observed during the sporadically visible solar eclipses were compared with the numerically extrapolated field-line structures of coronal magnetic field. A characteristic relationship between the observed structures of coronal plasma and the magnetic field line configurations was determined. The long-term evolution of large scale coronal structures inferred from photospheric magnetic observations in the course of 11- and 22-year solar cycles is described.Some known parameters, such as the source surface radius, or coronal rotation rate are discussed and actually interpreted. A relation between the large-scale photospheric magnetic field evolution and the coronal structure rearrangement is demonstrated.

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.

Solar Internal Rotation and Dynamo Waves: A Two-Dimensional Asymptotic Solution in the Convection Zone

2000 ◽  
Vol 179 ◽  
pp. 379-380
Author(s):  
Gaetano Belvedere ◽  
Kirill Kuzanyan ◽  
Dmitry Sokoloff
Keyword(s):  
Magnetic Field ◽  
Asymptotic Solution ◽  
Internal Rotation ◽  
Convection Zone ◽  
General Idea ◽  
Dynamo Model ◽  
Axially Symmetric ◽  
Dynamo Action ◽  
Regeneration Rate ◽  
Dynamo Waves

Extended abstractHere we outline how asymptotic models may contribute to the investigation of mean field dynamos applied to the solar convective zone. We calculate here a spatial 2-D structure of the mean magnetic field, adopting real profiles of the solar internal rotation (the Ω-effect) and an extended prescription of the turbulent α-effect. In our model assumptions we do not prescribe any meridional flow that might seriously affect the resulting generated magnetic fields. We do not assume apriori any region or layer as a preferred site for the dynamo action (such as the overshoot zone), but the location of the α- and Ω-effects results in the propagation of dynamo waves deep in the convection zone. We consider an axially symmetric magnetic field dynamo model in a differentially rotating spherical shell. The main assumption, when using asymptotic WKB methods, is that the absolute value of the dynamo number (regeneration rate) |D| is large, i.e., the spatial scale of the solution is small. Following the general idea of an asymptotic solution for dynamo waves (e.g., Kuzanyan & Sokoloff 1995), we search for a solution in the form of a power series with respect to the small parameter |D|–1/3(short wavelength scale). This solution is of the order of magnitude of exp(i|D|1/3S), where S is a scalar function of position.

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.

Polar Magnetic Field Reversals of the Sun in Maunder Minimum

2000 ◽  
Vol 179 ◽  
pp. 193-196
Author(s):  
V. I. Makarov ◽  
A. G. Tlatov
Keyword(s):  
Magnetic Field ◽  
Maunder Minimum ◽  
The Sun ◽  
Annual Rings ◽  
Field Reversal ◽  
Polar Magnetic Field ◽  
Pine Trees ◽  
Using Data ◽  
Magnetic Field Reversal

AbstractA possible scenario of polar magnetic field reversal of the Sun during the Maunder Minimum (1645–1715) is discussed using data of magnetic field reversals of the Sun for 1880–1991 and the14Ccontent variations in the bi-annual rings of the pine-trees in 1600–1730 yrs.

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