Coronal Holes in Global Complexes of Activity

This paper provides insight into heliospheric processes and galactic cosmic ray (GCR) modulation occurring due to the presence of two branches of solar activity in this solar layer. According to the topology of solar magnetic fields, these branches are called toroidal (active regions, sunspots, flares, coronal mass ejections, etc.) and poloidal (high-latitude magnetic fields, polar coronal holes, zonal unipolar magnetic regions, etc.). The main cause of different manifestations of the two branches on the solar surface and in the heliosphere — the layer at the base of the heliosphere in which the main energetic factor is the magnetic field — is formulated. In this case, the magnetic fields of the poloidal branch, which have a larger scale but a lower intensity, gain an advantage in penetrating into the heliosphere. A connection is shown between the poloidal branch and the heliospheric characteristics (solar wind velocity field, size of the heliosphere, form of the heliospheric current sheet, regular heliospheric magnetic field and its fluctuations) that, according to modern notions, determine GCR propagation in the heliosphere.

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MANIFESTATIONS OF TWO BRANCHES OF SOLAR ACTIVITY IN THE HELIOSPHERE AND GCR INTENSITY

Solnechno-Zemnaya Fizika ◽

10.12737/szf-54201902 ◽

2019 ◽

Vol 5 (4) ◽

pp. 12-25

Author(s):

Mikhail Krainev

Keyword(s):

Magnetic Field ◽

Solar Activity ◽

Magnetic Fields ◽

Coronal Holes ◽

Active Regions ◽

Cosmic Ray ◽

Heliospheric Current Sheet ◽

Field Size ◽

Galactic Cosmic Ray ◽

The Magnetic Field

This paper provides insight into heliospheric processes and galactic cosmic ray (GCR) modulation occurring due to the presence of two branches of solar activity in this solar layer. According to the topology of solar magnetic fields, these branches are called toroidal (active regions, sunspots, flares, coronal mass ejections, etc.) and poloidal (high-latitude magnetic fields, polar coronal holes, zonal unipolar magnetic regions, etc.). The main cause of different manifestations of the two branches on the solar surface and in the heliosphere — the layer at the base of the heliosphere in which the main energetic factor is the magnetic field — is formulated. In this case, the magnetic fields of the poloidal branch, which have a larger scale but a lower intensity, gain an advantage in penetrating into the heliosphere. A connection is shown between the poloidal branch and the heliospheric characteristics (solar wind velocity field, size of the heliosphere, form of the heliospheric current sheet, regular heliospheric magnetic field and its fluctuations) that, according to modern notions, determine GCR propagation in the heliosphere.

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Emergence of Twisted Magnetic Flux Related Sigmoidal Brightening

International Astronomical Union Colloquium ◽

10.1017/s0252921100064630 ◽

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.

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Nonlinear force-free modeling of magnetic fields in flare-productive active regions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316000387 ◽

2015 ◽

Vol 11 (S320) ◽

pp. 167-174

Author(s):

M. S. Wheatland ◽

S. A. Gilchrist

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Boundary Data ◽

Numerical Solutions ◽

Free Field ◽

Active Regions ◽

Coronal Magnetic Field ◽

Nonlinear Force ◽

The Magnetic Field ◽

Force Free Field

AbstractWe review nonlinear force-free field (NLFFF) modeling of magnetic fields in active regions. The NLFFF model (in which the electric current density is parallel to the magnetic field) is often adopted to describe the coronal magnetic field, and numerical solutions to the model are constructed based on photospheric vector magnetogram boundary data. Comparative tests of NLFFF codes on sets of boundary data have revealed significant problems, in particular associated with the inconsistency of the model and the data. Nevertheless NLFFF modeling is often applied, in particular to flare-productive active regions. We examine the results, and discuss their reliability.

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Observations of magnetic and kinetic helicity proxies

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313002160 ◽

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.

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Oscillatory convection in strong magnetic fields and origin of active regions

Symposium - International Astronomical Union ◽

10.1017/s0074180900021410 ◽

1968 ◽

Vol 35 ◽

pp. 127-130 ◽

Cited By ~ 1

Author(s):

S. I. Syrovatsky ◽

Y. D. Zhugzhda

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Active Regions ◽

Oscillatory Convection ◽

Strong Magnetic Fields ◽

Various Boundary Conditions ◽

Convective Cells ◽

The Magnetic Field ◽

Polytropic Atmosphere

The convection in a compressible inhomogeneous conducting fluid in the presence of a vertical uniform magnetic field has been studied. It is shown that a new mode of oscillatory convection occurs, which exists in arbitrarily strong magnetic fields. The convective cells are stretched along the magnetic field, their horizontal dimensions are determined by radiative cooling. Criteria for convective instability in a polytropic atmosphere are obtained for various boundary conditions in the case when the Alfvén velocity is higher compared with the velocity of sound.The role of oscillatory convection in the origin of sunspots and active regions is discussed.

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Examining the optical intensity and magnetic field expansion factor in the open magnetic field regions associated with coronal holes

Proceedings of the International Astronomical Union ◽

10.1017/s1743921320000393 ◽

2019 ◽

Vol 15 (S354) ◽

pp. 228-231

Author(s):

Chia-Hsien Lin ◽

Guan-Han Huang ◽

Lou-Chuang Lee

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Coronal Holes ◽

Closed Field ◽

Logarithmic Scale ◽

Expansion Factor ◽

Astrophysical Journal ◽

Field Lines ◽

The Relationship ◽

Open Magnetic Field

AbstractCoronal holes can be identified as the darkest regions in EUV or soft X-ray images with predominantly unipolar magnetic fields (LIRs) or as the regions with open magnetic fields (OMF). Our study reveals that only 12% of OMF regions are coincident with LIRs. The aim of this study is to investigate the conditions that affect the EUV intensity of OMF regions. Our results indicate that the EUV intensity and the magnetic field expansion factor of the OMF regions are weakly positively correlated when plotted in logarithmic scale, and that the bright OMF regions are likely to locate inside or next to the regions with closed field lines. We empirically determined a linear relationship between the expansion factor and the EUV intensity. The relationship is demonstrated to improve the consistency from 12% to 23%. The results have been published in Astrophysical Journal (Huang et al. 2019).

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Cyclotron Lines in the Spectra of Solar Flares and Solar Active Regions

International Astronomical Union Colloquium ◽

10.1017/s025292110003205x ◽

1989 ◽

Vol 104 (1) ◽

pp. 449-456

Author(s):

V. V. Zheleznyakov ◽

E. Ya. Zlotnik

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Cross Section ◽

Active Regions ◽

Kinetic Temperature ◽

Magnetic Tube ◽

Tube Cross Section ◽

Solar Active Regions ◽

Electron Gyrofrequency ◽

The Magnetic Field

AbstractIt was shown by Zheleznyakov and Zlotnik (1980a, b) that in complex configurations of solar magnetic fields (in hot loops above the active centres, in neutral current sheets in the preflare phase, in hot X-ray kernels in the initial flare phase) a system of cyclotron lines in the spectrum of microwave radiation is likely to be formed. Such a line was obtained by Willson (1985) in the VLA observations at harmonics of the electron gyrofrequency. This communication interprets these observations on the basis of an active region model in which thermal cyclotron radiation is produced by hot plasma filling the magnetic tube in the corona above a group of spots. In this model the frequency of the recorded 1658 MHz line corresponds to the third harmonic of electron gyrofrequency, which yields the magnetic field (196 + 4) G along the magnetic tube axis. The linewidth Af/f ∼ 0.1 is determined by the 10% inhomogeneity of the magnetic field over the cross-section of the tube; the line profile indicates the kinetic temperature distribution of electrons over the tube cross-section with the maximum value 4 x 106 K. Analysis shows that study of cyclotron lines can serve as an efficient tool for diagnostics of magnetic fields and plasma in the solar active regions and flares.

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Measurements of local magnetic fields in a solar flare by splitting of emissive peaks in cores of spectral lines

Bulletin of Taras Shevchenko National University of Kyiv Astronomy ◽

10.17721/btsnua.2018.57.47-52 ◽

2018 ◽

pp. 47-52 ◽

Cited By ~ 1

Author(s):

V. Lozitsky

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Solar Flare ◽

Filling Factor ◽

Spectral Lines ◽

Local Fields ◽

Strong Component ◽

Component Structure ◽

Local Magnetic Fields ◽

The Magnetic Field

We present study of solar flare of 19 July 2000 which arose in active region NOAA 9087 and had M 5.6 / 3N importance. Observational material was obtained with the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv. The local magnetic fields in this flare were measured by the splitting of emissive peaks of the FeI 5269.54, FeII 4923.93, Нα, Нβ, Нγand D3 HeI lines. The basic idea of the method is based on the fact that the flare emission in some spectral lines is clearly divided into two components: (1) wider and unpolarized, and (2) more narrow and polarized, with significant Zeeman splitting. This is indication to the two-component structure of the magnetic field, with substantially different magnetic fields and thermodynamical conditions in these two components. Due to the fact that the polarized emission is quite confidently separated from the unpolarized, it is possible to measure the local magnetic fields directly in the second (strong) component regardless of the filling factor. It was found that in the bright place of this flare, which was projected on the sunspot penumbra, the effective magnetic field Beff in the FeI 6301.5 i 6302.5 lines measured by splitting of the Fraunhofer profiles, was 900 G. However, the splitting of emissive peaks in Нα, Нβ, Нγ and D3 lines corresponds to 1000 G, 1400 G, 1450 G and about zero, respectively, with errors of 30-50 G for abovenamed FeI lines and about 100–150 G for other lines. This difference in the results is probably due to the fact that in the case of FeI 6301.5 i 6302.5 lines, the Beff value represents several parameters, including the value of the background field, the filling factor, and the intensity of the local fields in the strong component. In contrast, data on the Нα, Нβ, Нγ, and D3 lines mainly reflect local fields in the strong component and indicate the nonmonotonous distribution of the magnetic field with height in solar atmosphere, with its maximum at the chromospheric level. Earlier in this flare, when constructing its semi-empirical model, local amplification of the magnetic field at the photospheric level was discovered, and its value reached 1500 G. These data are confirmed by direct measurements of splitting of emissive peaks in FeI 5269.54 and FeII 4923.93 lines, according to which the magnetic field in the flare was 1250 ± 100 G. Thus, in this flare there were at least two regions (possibly two flat layers) of local amplification of the magnetic field.

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Evolution of a Filament/CH/Magnetic Field Complex

International Astronomical Union Colloquium ◽

10.1017/s0252921100047989 ◽

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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