Magnetic fields surrounding coronal holes

2008 ◽  
pp. 141-145
Author(s):  
Václav Bumba ◽  
Miroslav Klvaňa ◽  
Július Sýkora
Keyword(s):  
Magnetic Fields ◽  
Coronal Holes

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”.

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

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).

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.

scholarly journals Coronal Holes in Global Complexes of Activity

2015 ◽  
Vol 2015 ◽  
pp. 1-9
Author(s):  
Vladimir N. Obridko ◽  
Bertha D. Shelting
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Coronal Holes ◽  
Active Regions ◽  
Local Fields ◽  
Magnetic Region ◽  
Single Process ◽  
Global And Local ◽  
The Relationship ◽  
The Magnetic Field

We propose a new concept that considers the global complexes of activity as a combination of global and local fields. Traditionally, the complexes of activity have been identified from observations of active regions (ARs). Here, we show that a complex of activity comprises both (AR) and coronal holes (CHs). Our analysis is based on observations of magnetic fields of various scales, SOHO/MDI data, and UV observations of CH. The analysis has corroborated the existence of complexes of activity that involve AR and equatorial CH. Both AR and CH are embedded in an extended magnetic region dominated by the magnetic field of one sign, but not strictly unipolar. It is shown that the evolution of CH and AR is a single process. The relationship between the fields of various scales in the course of a cycle is discussed.

Examination of the EUV Intensity in the Open Magnetic Field Regions Associated with Coronal Holes

2020 ◽  
Author(s):  
Guan-Han Huang ◽  
Chia-Hsien Lin ◽  
Lou Chuang Lee
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Order Approximation ◽  
Coronal Holes ◽  
Closed Field ◽  
Spatial And Temporal Distributions ◽  
Field Lines ◽  
First Order Approximation ◽  
Log Normal ◽  
Open Magnetic Field

<p>Coronal holes can be identified as the regions with magnetic field lines extending far away from the Sun, or the darkest regions in EUV/X-ray images with predominantly unipolar magnetic fields. A comparison between the locations of our determined regions with open magnetic field lines (OMF) and regions with low EUV intensity (LIR) reveals that only 12% of the OMF regions coincide with the LIRs. The aim of this study is to investigate the conditions leading to the different brightnesses of OMF regions, and to provide a means to predict whether an OMF region would be bright or dark. Examining the statistical distribution profiles of the magnetic field expansion factor (f<sub>s</sub>) and Atmospheric Imaging Assembly 193 Å intensity (I<sub>193</sub>) reveals that both profiles are approximately log-normal. The analysis of the spatial and temporal distributions of f<sub>s</sub> and I<sub>193</sub> indicates that the bright OMF regions often are inside or next to regions with closed field lines, including quiet-Sun regions and regions with strong magnetic fields. Examining the relationship between I<sub>193</sub> and f<sub>s</sub> reveals a weak positive correlation between log I<sub>193</sub> and log f<sub>s</sub> , with a correlation coefficient ≈ 0.39. As a first-order approximation, the positive relationship is determined to be log I<sub>193</sub> = 0.62 log f<sub>s</sub> + 1.51 based on the principle of the whitening/dewhitening transformation. This linear relationship is demonstrated to increase the consistency between the OMF regions and LIRs from 12% to 23%.</p>

scholarly journals Polar magnetic fields and coronal holes during the recent solar minima

2011 ◽  
Vol 7 (S286) ◽  
pp. 101-112 ◽  
Author(s):  
Giuliana de Toma
Keyword(s):  
Solar Wind ◽  
Magnetic Fields ◽  
Coronal Holes ◽  
Magnetic Activity ◽  
Fast Solar Wind ◽  
The Earth ◽  
Slow Decline ◽  
Polar Magnetic Fields ◽  
Cycle 24 ◽  
The One

AbstractThe slow decline of solar Cycle 23 combined with the slow rise of Cycle 24 resulted in a very long period of low magnetic activity during the years 2007–2009 with sunspot number reaching the lowest level since 1913. This long solar minimum was characterized by weak polar magnetic fields, smaller polar coronal holes, and a relatively complex coronal morphology with multiple streamers extending to mid latitudes. At the same time, low latitude coronal holes remained present on the Sun until the end of 2008 modulating the solar wind at the Earth in co-rotating, fast solar wind streams. This magnetic configuration was remarkably different from the one observed during the previous two solar minima when coronal streamers were confined near the equator and the fast solar wind was mainly originating from the large coronal holes around the Sun's poles. This paper presents the evolution of the polar magnetic fields and coronal holes during the past minimum, compare it with the previous minima, and discuss the implications for the solar wind near the Earth. It also considers the minimum of Cycle 23 in an historical perspective and, in particular, compares it to the long minima at the turn of the 19th century.

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.

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.

On the nature of photospheric magnetic fields beneath large coronal holes

Solar Physics ◽  
1977 ◽  
Vol 55 (1) ◽  
pp. 83-97 ◽  
Author(s):  
S. Frankenthal ◽  
A. S. Krieger
Keyword(s):  
Magnetic Fields ◽  
Coronal Holes
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