Coronal Holes and Photospheric Magnetic Field

1994 ◽  
Vol 144 ◽  
pp. 47-51 ◽  
Author(s):  
V. Bumba ◽  
M. Klvaňa ◽  
J. Sýkora
Keyword(s):  
Magnetic Field ◽  
Spectral Line ◽  
Intensity Distribution ◽  
Solar Surface ◽  
Coronal Holes ◽  
Active Regions ◽  
Velocity Fields ◽  
Doppler Velocity ◽  
Spectral Line Intensity ◽  
The Continuum

Since the reconstruction of the photoelectric magnetograph of the Ondřejov Observatory in 1990 (Klvaňa and Bumba, 1994; Klvaňaet al., 1994), several hundred sets of measurements (mostly in the line FeI 5253.47 Å) have been obtained during 1991 and 1992. The longitudinal magnetic and Doppler velocity fields, as well as the continuum spectral line intensity distribution in more than one hundred areas on the solar surface have been investigated (the measurements of one region were usually repeated several times). Often a relatively large part of the solar disk was studied.Comparing the measured areas with the distribution of active regions and other activity phenomena on the Hα Synoptic Charts, it has been found that some of the measurements were distributed very favorably around coronal holes, sometimes covering smaller parts and in a few cases even larger parts of their areas.

scholarly journals Two classes of eruptive events during Solar Minimum

2021 ◽  
Author(s):  
Prantika Bhowmik ◽  
Anthony Yeates
Keyword(s):  
Magnetic Field ◽  
Free Energy ◽  
Magnetic Flux ◽  
Solar Minimum ◽  
Large Scale ◽  
Solar Surface ◽  
Coronal Holes ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
The Magnetic Field

<p>During Solar Minimum, the Sun is perceived to be quite inactive with barely any spots emerging on the solar surface. Consequently, we observe a drop in the number of highly energetic events such as solar flares and coronal mass ejections (CMEs), which are often associated with active regions on the photosphere. However, our magnetofrictional simulations during the minimum period suggest that the solar corona could still be significantly dynamic while evolving in response to the large-scale shearing velocities on the solar surface. The non-potential evolution of the corona leads to the accumulation of magnetic free energy and helicity, which is periodically lost through eruptive events. Our study shows that these events can be categorised into two distinct classes. One set of events are caused due to full-scale eruption of low-lying coronal flux ropes and could be associated with occasional filament erupting CMEs observed during Solar Minimum. The other set of events are not driven by destabilisation of low-lying structures but rather by eruption from overlying sheared arcades. These could be linked with streamer blowouts or stealth CMEs. The two classes differ considerably in the amount of magnetic flux and helicity shed through the outer coronal boundary. We additionally investigate how other measurables such as current, open magnetic flux, free energy, coronal holes area, and the horizontal component of the magnetic field on the outer model boundary vary during the two classes of event. This study demonstrates and emphasises the importance and necessity of understanding the dynamics of the coronal magnetic field during Solar Minimum.</p>

scholarly journals The Evolution of the Solar Magnetic Field

2012 ◽  
Vol 10 (H16) ◽  
pp. 86-89 ◽  
Author(s):  
J. Todd Hoeksema
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Solar Magnetic Field ◽  
Coronal Holes ◽  
Active Regions ◽  
Statistical Characteristics ◽  
Field Pattern ◽  
Small Scale ◽  
Polar Caps ◽  
Magnetic Elements

AbstractThe almost stately evolution of the global heliospheric magnetic field pattern during most of the solar cycle belies the intense dynamic interplay of photospheric and coronal flux concentrations on scales both large and small. The statistical characteristics of emerging bipoles and active regions lead to development of systematic magnetic patterns. Diffusion and flows impel features to interact constructively and destructively, and on longer time scales they may help drive the creation of new flux. Peculiar properties of the components in each solar cycle determine the specific details and provide additional clues about their sources. The interactions of complex developing features with the existing global magnetic environment drive impulsive events on all scales. Predominantly new-polarity surges originating in active regions at low latitudes can reach the poles in a year or two. Coronal holes and polar caps composed of short-lived, small-scale magnetic elements can persist for months and years. Advanced models coupled with comprehensive measurements of the visible solar surface, as well as the interior, corona, and heliosphere promise to revolutionize our understanding of the hierarchy we call the solar magnetic field.

scholarly journals Source-region characteristics of anemone active regions in the ascending phase of solar cycle 24

2020 ◽  
Vol 642 ◽  
pp. A233
Author(s):  
R. Sharma ◽  
C. Cid
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Minimum Distance ◽  
Source Region ◽  
Coronal Holes ◽  
Active Regions ◽  
Yearly Average ◽  
Solar Cycle 24 ◽  
Cycle 24 ◽  
Rise Phase

Context. Active regions in close proximity to coronal holes, also known as anemone regions, are the best candidates for studying the interaction between closed and open magnetic field topologies at the Sun. Statistical investigation of their source-region characteristics can provide vital clues regarding their possible association with energetic events, relevant from space weather perspectives. Aims. The main goal of our study is to understand the distinct properties of flaring and non-flaring anemone active regions and their host coronal holes, by examining spatial and magnetic field distributions during the rise phase of the solar cycle, in the years 2011–2014. Methods. Anemone regions were identified from the minimum-distance threshold, estimated using the data available in the online catalogs for on-disk active regions and coronal holes. Along with the source-region area and magnetic field characteristics, associated filament and flare cases were also located. Regions with and without flare events were further selected for a detailed statistical examination to understand the major properties of the energetic events, both eruptive and confined, at the anemone-type active regions. Results. Identified anemone regions showed weak asymmetry in their spatial distribution over the solar disk, with yearly average independent from mean sunspot number trend, during the rise phase of solar cycle 24. With the progression in solar cycle, the area and minimum-distance parameters indicated a decreasing trend in their magnitudes, while the magnetic field characteristics indicated an increase in their estimated magnitudes. More than half of the regions in our database had an association with a filament structure, and nearly a third were linked with a magnetic reconnection (flare) event. Anemone regions with and without flares had clear distinctions in their source-region characteristics evident from the distribution of their properties and density analysis. The key differences included larger area and magnetic field magnitudes for flaring anemone regions, along with smaller distances between the centers of the active region and its host coronal hole.

A Discussion on the physics of the solar atmosphere - Physics of the solar atmosphere

1976 ◽  
Vol 281 (1304) ◽  
pp. 415-426
Keyword(s):  
Magnetic Field ◽  
Transition Region ◽  
Solar Atmosphere ◽  
Solar Rotation ◽  
Active Regions ◽  
Rotation Velocity ◽  
Coronal Magnetic Field ◽  
Velocity Fields ◽  
Field Structure ◽  
Magnetic Field Structure

A summary is given on recent results on the physics of the quiet solar atmosphere, and active regions. This includes: solar rotation, velocity fields and waves, magnetic field concentration, the transition region, coronal magnetic field structure, and prominences.

scholarly journals Variations of the Coronal Radiation in X-ray Related to Coronal Holes, Active Region Loop Systems, Bright Points

1994 ◽  
Vol 143 ◽  
pp. 159-171
Author(s):  
Ester Antonucci
Keyword(s):  
Magnetic Field ◽  
Spatial Distribution ◽  
Large Scale ◽  
Coronal Holes ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Small Scale ◽  
X Ray ◽  
Coronal Structures

The coronal features observed in X-ray emission, varying from the small-scale, short-lived bright points to the large-scale, long-lived coronal holes, are closely associated with the coronal magnetic field and its topology, and their variability depends strongly on the solar cycle. Here we discuss the spatial distribution of the coronal structures, the frequency distribution of the brightness variations in active regions, and the role of magnetic reconnection in determining the variability of the coronal features, on the basis of the new observations of the soft X-ray emission recently obtained with the Yohkoh satellite and the NIXT experiment.

scholarly journals Evolving Features of Hβ Doppler Velocity Fields at Sites of Flares

1993 ◽  
Vol 141 ◽  
pp. 267-270
Author(s):  
Wei Li ◽  
Guoxiang Ai ◽  
Hongqi Zhang
Keyword(s):  
Velocity Field ◽  
Active Regions ◽  
Velocity Fields ◽  
Time Sequence ◽  
Line Of Sight ◽  
Doppler Velocity

AbstractWe analyzed eight active regions with more than 600 flare kernels and ribbons, and relevant time sequence Hβ chromospheric Dopplergrams. These data showed that during several hours prior to the flares, the velocity field evolves so that the sites of the flare kernels and ribbons become close to the inversion line of the velocity field. This result holds regardless of whether or not the flare sites are wholly located in blue-shifted areas, or are far from the the inversion line of the line-of-sight velocity field, or are partly within red-shifted areas.

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.

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

2019 ◽  
Vol 5 (4) ◽  
pp. 10-20
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.

scholarly journals The balance of magnetic fluxes in active regions

1968 ◽  
Vol 35 ◽  
pp. 47-49 ◽  
Author(s):  
Jan Olof Stenflo
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Active Region ◽  
Solar Surface ◽  
Active Regions ◽  
Basic Feature ◽  
The Sun ◽  
Magnetic Disturbance ◽  
The Magnetic Field

According to modern theories of the solar cycle, active regions on the Sun are caused by a magnetic disturbance penetrating the solar surface from below. Sunspots, filaments, flares and other conspicuous events in an active region seem to be only secondary phenomena, the basic feature being the magnetic field itself.

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