Formation of Coronal Holes and the Global Magnetic Field Distribution

1994 ◽  
Vol 144 ◽  
pp. 65-67 ◽  
Author(s):  
V. Bumba ◽  
M. Klvaňa ◽  
V. Rušin ◽  
M. Rybanský ◽  
G. T. Buyukliev
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Coronal Holes ◽  
Activity Cycle ◽  
Close Relation ◽  
Solar Activity Cycle ◽  
Cycle Maximum ◽  
Global Magnetic Field ◽  
Mutual Relations ◽  
The Individual

The photoelectric magnetograph of the Ondřejov Observatory was reconstructed in 1990 (Klvaňa and Bumba, 1994; Klvaňaet al, 1994). During 1991 and 1992, several hundred sets of measurements were obtained, mostly in line Fel 5253.47 Å. It has been found that some of the measurements are distributed very favorably around coronal holes, sometimes covering smaller parts and in a few cases even larger parts of their areas.Both 1991 and 1992 were exceptional as regards their relation to the phase of the ending solar activity cycle (No 22): while the period of the secondary cycle maximum (mainly the southern solar hemisphere) took place in 1991, the year 1992 coincided with the initial stage of its declining branch. Since the formation of coronal holes is in close relation to the dynamics of the global distribution of solar magnetic fields, we thought that before starting to investigate the detailed connections of the individual coronal holes with particular local magnetic fields, it might be interesting to study their mutual relations also on a large scale.

Remote Sensing of the Heliospheric Solar Wind using Radio Astronomy Methods and Numerical Simulations

2000 ◽  
Vol 179 ◽  
pp. 439-444
Author(s):  
S. Ananthakrishnan
Keyword(s):  
Solar Wind ◽  
Radio Astronomy ◽  
High Speed ◽  
Coronal Holes ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Maximum Activity ◽  
Closed Field ◽  
Cycle Maximum ◽  
Speed Solar Wind

AbstractThe ground-based radio astronomy method of interplanetary scintillations (IPS) and spacecraft observations have shown, in the past 25 years, that while coronal holes give rise to stable, recurring high speed solar wind streams during the minimum of the solar activity cycle, the slow speed wind seen more during the solar maximum activity is better associated with the closed field regions, which also give rise to solar flares and coronal mass ejections (CME’s). The latter events increase significantly, as the cycle maximum takes place. We have recently shown that in the case of energetic flares one may be able to track the associated disturbances almost on a one to one basis from a distance of 0.2 to 1 AU using IPS methods. Time dependent 3D MHD models which are constrained by IPS observations are being developed. These models are able to simulate general features of the solar-generated disturbances. Advances in this direction may lead to prediction of heliospheric propagation of these disturbances throughout the solar system.

scholarly journals Magnetic Fields in Disks and Halos of Spiral Galaxies

1991 ◽  
Vol 144 ◽  
pp. 267-280 ◽  
Author(s):  
Rainer Beck
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Coronal Holes ◽  
Azimuthal Angle ◽  
Total Strength ◽  
Radio Halo ◽  
Star Formation Activity ◽  
Energy Equipartition ◽  
Field Lines

Spiral galaxies host interstellar magnetic fields of 4-15 μG total strength. A significant fraction of the field lines shows large-scale structures. At face-on or moderately inclined view, the field lines run generally parallel to the spiral arms, either with uniform direction with respect to azimuthal angle (axisymmetric spiral, ASS), with one reversal along azimuthal angle (bisymmetric spiral, BSS), or with spiral orientation without dominating direction.At edge-on view, the field is concentrated in a thin disk, often surrounded by a thick radio disk with field lines mostly parallel to the plane, similar to the quadrupole-type dynamo field. Radio polarization data from NGC891 indicate that the thermal gas seen in Hα is responsible for Faraday depolarization. The required scaleheight of the field of ~4 kpc is comparable to the value expected in case of energy equipartition between magnetic fields and cosmic rays. The interacting edge-on galaxy NGC 4631 shows a much larger radio halo with field lines perpendicular to the disk, possibly driven by a strong galactic wind or the result of a dipole-type halo field.Field lines bending out of the plane are also visible in face-on galaxies as regions with high rotation measures and low star-formation activity. The resemblance to the phenomenon of the solar corona suggests to call them “galactic coronal holes”.

scholarly journals Asymptotic Model for Large-Scale Quasiheliostrophic Flow

1993 ◽  
Vol 157 ◽  
pp. 135-139
Author(s):  
Mihai Ghizaru
Keyword(s):  
Large Scale ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Mhd Equations ◽  
Asymptotic Model ◽  
Regular Perturbation ◽  
Atmospheric Flow ◽  
Flux Function ◽  
Magnetohydrodynamic Model ◽  
Suitable Framework

Starting from the ideal MHD equations written in spherical coordinates, using the regular perturbation method, quasiheliostrophic equations are derived as generalisation of quasigeostrophic models for atmospheric flow. From the fourth order momentum and induction equations, two prognostic equations for the stream function and magnetic flux function are derived. The magnetohydrodynamic model based on these equations is a suitable framework for describing the interaction between large-scale dynamic and magnetic features and the presence of specific patterns like active longitudes in the solar activity cycle.

Large-scale distribution of magnetic fields, green corona and prominences during an extended activity cycle

Solar Physics ◽  
1990 ◽  
Vol 128 (1) ◽  
pp. 253-259 ◽  
Author(s):  
Václav Bumba ◽  
Vojtech Rušin ◽  
Milan Rybanský
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Activity Cycle

scholarly journals Large-Scale Magnetic Structures Responsible for Coronal Disturbances

1974 ◽  
Vol 57 ◽  
pp. 73-83 ◽  
Author(s):  
V. Bumba ◽  
J. Sýkora
Keyword(s):  
Large Scale ◽  
Coronal Holes ◽  
Life Time ◽  
Activity Cycle ◽  
Negative Polarity ◽  
Longitudinal Distribution ◽  
Time Interval ◽  
Flare Activity ◽  
Positive Polarity ◽  
Coronal Emission

In the first part of our communication, in a short summary of our recent results, it is demonstrated that over the last 15 years (the time interval for which the magnetic synoptic charts are available) the largest solar activity, usually connected with proton-flare occurrence, has been very closely related to a characteristic large-scale pattern in the magnetic field distribution with a life-time of the order of 8–10 solar rotations. These regular features are seen in the negative as well as in the positive polarity, although they can be seen better in the negative polarity where their forms are more pronounced, regardless of the activity cycle. The form alternates with the location in the northern or the southern solar hemispheres due to the mutual relations of both polarities, individual active regions, the influence of the differential rotations, the shift in longitude, etc. This pattern could be observed up to the large August 1972 proton-flare activity.The large-scale magnetic patterns described are accompanied by characteristic large-scale features in the green (λ 5303) coronal emission, presented in the form of isophotes on the synoptic charts (reduced to a unified photometric scale).In the second part of the presentation, preliminary results, concerning the correlation of the longitudinal distribution of the green coronal emission with the negative and the positive polarity fields for two time intervals (August 1960–September 1961 and January 1969–December 1969) are described. The existence of two ‘coronal active longitudes’ in both intervals, as well as the close relation of these longitudinal emission maxima to certain parts of the large-scale characteristic bodies of negative polarity, is discussed. Also, the existence of one heliographic longitude, connected with ‘coronal holes’ (minimal green corona emission), and its relation to the positive polarity large-scale pattern are proved.

Solar Wind Variation with the Cycle

2000 ◽  
Vol 179 ◽  
pp. 423-429
Author(s):  
I. S. Veselovsky ◽  
A. V. Dmitriev ◽  
A. V. Suvorova ◽  
M. V. Tarsina
Keyword(s):  
Solar Wind ◽  
Coronal Holes ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Time Dependent ◽  
Solar Cycles ◽  
Solar Wind Density ◽  
Plasma Parameters ◽  
Decadal Variations ◽  
Wind Measurements

AbstractThe cyclic evolution of the heliospheric plasma parameters is related to the time-dependent boundary conditions in the solar corona. “Minimal” coronal configurations correspond to the regular appearance of the tenuous, but hot and fast plasma streams from the large polar coronal holes. The denser, but cooler and slower solar wind is adjacent to coronal streamers. Irregular dynamic manifestations are present in the corona and the solar wind everywhere and always. They follow the solar activity cycle rather well. Because of this, the direct and indirect solar wind measurements demonstrate clear variations in space and time according to the minimal, intermediate and maximal conditions of the cycles. The average solar wind density, velocity and temperature measured at the Earth’s orbit show specific decadal variations and trends, which are of the order of the first tens per cent during the last three solar cycles. Statistical, spectral and correlation characteristics of the solar wind are reviewed with the emphasis on the cycles.

scholarly journals Direct evidence of a full dipole flip during the magnetic cycle of a sun-like star

2018 ◽  
Vol 620 ◽  
pp. L11 ◽  
Author(s):  
S. Boro Saikia ◽  
T. Lueftinger ◽  
S. V. Jeffers ◽  
C. P. Folsom ◽  
V. See ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Activity Cycle ◽  
Doppler Imaging ◽  
Dipolar Field ◽  
Magnetic Cycle ◽  
Activity Maximum ◽  
Cycle Minimum ◽  
Chromospheric Activity ◽  
Cycle Maximum

Context.The behaviour of the large-scale dipolar field, during a star’s magnetic cycle, can provide valuable insight into the stellar dynamo and associated magnetic field manifestations such as stellar winds.Aims.We investigate the temporal evolution of the dipolar field of the K dwarf 61 Cyg A using spectropolarimetric observations covering nearly one magnetic cycle equivalent to two chromospheric activity cycles.Methods.The large-scale magnetic field geometry is reconstructed using Zeeman Doppler imaging, a tomographic inversion technique. Additionally, the chromospheric activity is also monitored.Results.The observations provide an unprecedented sampling of the large-scale field over a single magnetic cycle of a star other than the Sun. Our results show that 61 Cyg A has a dominant dipolar geometry except at chromospheric activity maximum. The dipole axis migrates from the southern to the northern hemisphere during the magnetic cycle. It is located at higher latitudes at chromospheric activity cycle minimum and at middle latitudes during cycle maximum. The dipole is strongest at activity cycle minimum and much weaker at activity cycle maximum.Conclusions.The behaviour of the large-scale dipolar field during the magnetic cycle resembles the solar magnetic cycle. Our results are further confirmation that 61 Cyg A indeed has a large-scale magnetic geometry that is comparable to the Sun’s, despite being a slightly older and cooler K dwarf.

scholarly journals Evolution of a Filament/CH/Magnetic Field Complex

1998 ◽  
Vol 167 ◽  
pp. 393-396
Author(s):  
B.A. Ioshpa ◽  
E.I. Mogilevsky ◽  
V.N. Obridko
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Magnetic Fields ◽  
Large Scale ◽  
Coronal Holes ◽  
Field Structure ◽  
Potential Approximation ◽  
Magnetic Field Structure ◽  
Single Complex ◽  
The Magnetic Field

AbstractSOHO and YOHKOH images, as well as Hα filtergrams and magnetograms from IZMIRAN have been used to analyze the evolution of the related solar phenomena – filament, active region, and accompanying pair of coronal holes – during six solar rotations, with an emphasis on the events observed during August–September, 1996. The whole complex has been considered against the large–scale magnetic fields calculated under the potential approximation. A peculiar point has been found along the changing filament. It is shown that the phenomena under investigation (filament, active region, and coronal hole) form a single complex connected with the magnetic field structure.

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