The formation of a penumbra as observed with the German VTT and SoHO/MDI

AbstractThe generation of magnetic flux in the solar interior and its transport to the outer solar atmosphere will be in the focus of solar physics research for the next decades. One key-ingredient is the process of magnetic flux emergence into the solar photosphere, and the reorganization to form the magnetic phenomena of active regions like sunspots and pores.On July 4, 2009, we observed a region of emerging magnetic flux, in which a proto-spot without penumbra forms a penumbra within some 4.5 hours. This process is documented by multi-wavelength observations at the German VTT: (a) imaging, (b) data with high resolution and temporal cadence acquired in Fe I 617.3 nm with the 2D imaging spectropolarimter GFPI, and (c) scans with the slit based spectropolarimeter TIP in Fe I 1089.6 nm. MDI contiuum maps and magnetograms are used to follow the formation of the proto-spot, and the subsequent evolution of the entire active region.During the formation of the penumbra, the area and the magnetic flux of the spot increases. The additional magnetic flux is supplied by the adjacent region of emerging magnetic flux: As emerging bipole separate, the poles of the spot polarity migrate towards the spot, and finally merge with it. As more and more flux is accumulated, a penumbra forms. From inversions we infer maps for the magnetic field and the Doppler velocity (being constant along the line-of-sight). We calculate the magnetic flux of the forming spot and of the bipole footpoints that merge with the proto-spot. We witness the onset of the Evershed flow and the associated enhance of the field inclination as individual penumbral filaments form. Prior to the formation of individual penumbral sectors we detect the existence of ‘counter’ Evershed flows. These in-flows turn into the classical radial Evershed outflows as stable penumbra segments form.

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Study of helicity properties of peculiar active regions

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309992493 ◽

2009 ◽

Vol 5 (S264) ◽

pp. 102-104 ◽

Cited By ~ 1

Author(s):

M. C. López Fuentes ◽

C. H. Mandrini ◽

P. Démoulin

Keyword(s):

Magnetic Field ◽

Magnetic Flux ◽

Active Regions ◽

Solar Interior ◽

Magnetic Helicity ◽

Flux Tubes ◽

Origin And Evolution ◽

Magnetic Structures ◽

Magnetic Flux Tubes ◽

The Magnetic Field

AbstractPeculiar solar active regions (ARs), such as δ-islands and other high tilt bipoles, are commonly associated with the emergence of severely deformed magnetic flux tubes. Therefore, the study of these ARs provides valuable information on the origin and evolution of magnetic structures in the solar interior. Here, we infer the magnetic helicity properties of the flux tubes associated to a set of peculiar ARs by studying the evolution of photospheric magnetograms (SOHO/MDI) and coronal observations (SOHO/EIT and TRACE) in combination with force-free models of the magnetic field. We discuss how our results relate to different models of the evolution of emerging magnetic flux tubes.

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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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Solar magneto-convection

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313002329 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 95-106 ◽

Cited By ~ 4

Author(s):

Manfred Schüssler

Keyword(s):

Active Regions ◽

Small Scale ◽

Solar Photosphere ◽

Surface Layers ◽

Dynamo Action ◽

Near Surface ◽

Wide Range ◽

Recent Developments ◽

Mixed Polarity ◽

The Magnetic Field

AbstractAn overview is given about recent developments and results of comprehensive simulations of magneto-convective processes in the near-surface layers and photosphere of the Sun. Simulations now cover a wide range of phenomena, from whole active regions, over individual sunspots and pores, magnetic flux concentrations and vortices in intergranular lanes, down to the intricate mixed-polarity structure of the magnetic field generated by small-scale dynamo action. The simulations in concert with high-resolution observations have provided breakthroughs in our understanding of the structure and dynamics of the magnetic fields in the solar photosphere.

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Solar photosphere magnetization

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935244 ◽

2020 ◽

Vol 634 ◽

pp. A40 ◽

Cited By ~ 1

Author(s):

Véronique Bommier

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Field Gradient ◽

Magnetic Field Gradient ◽

Active Regions ◽

Spectral Lines ◽

Solar Interior ◽

Solar Photosphere ◽

Total Charge ◽

Solar Active Regions

Context. A recent review shows that observations performed with different telescopes, spectral lines, and interpretation methods all agree about a vertical magnetic field gradient in solar active regions on the order of 3 G km−1, when a horizontal magnetic field gradient of only 0.3 G km−1 is found. This represents an inexplicable discrepancy with respect to the divB = 0 law. Aims. The objective of this paper is to explain these observations through the law B = μ0(H + M) in magnetized media. Methods. Magnetization is due to plasma diamagnetism, which results from the spiral motion of free electrons or charges about the magnetic field. Their usual photospheric densities lead to very weak magnetization M, four orders of magnitude lower than H. It is then assumed that electrons escape from the solar interior, where their thermal velocity is much higher than the escape velocity, in spite of the effect of protons. They escape from lower layers in a quasi-static spreading, and accumulate in the photosphere. By evaluating the magnetic energy of an elementary atom embedded in the magnetized medium obeying the macroscopic law B = μ0(H + M), it is shown that the Zeeman Hamiltonian is due to the effect of H. Thus, what is measured is H. Results. The decrease in density with height is responsible for non-zero divergence of M, which is compensated for by the divergence of H, in order to ensure div B = 0. The behavior of the observed quantities is recovered. Conclusions. The problem of the divergence of the observed magnetic field in solar active regions finally reveals evidence of electron accumulation in the solar photosphere. This is not the case of the heavier protons, which remain in lower layers. An electric field would thus be present in the solar interior, but as the total charge remains negligible, no electric field or effect would result outside the star.

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Imaging sunspots using helioseismic methods

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2005.1647 ◽

2005 ◽

Vol 363 (1837) ◽

pp. 2761-2775 ◽

Cited By ~ 7

Author(s):

C.H Tong

Keyword(s):

Seismic Imaging ◽

Structural Characteristics ◽

Imaging Techniques ◽

Solar Physics ◽

Interdisciplinary Approach ◽

Active Regions ◽

Solar Interior ◽

Seismic Methods ◽

New Research ◽

First Time

The origin of sunspots is one of the most fundamental and yet poorly understood areas in solar physics. Imaging local anomalous features in the solar interior offers a direct way to unravel the underlying physical processes of sunspots and the mechanisms behind their formation. The advent of local helioseismology in the last few years has, for the first time, made it possible to image local internal solar structures. High-resolution satellite and ground telescope data which reveal the details of the vibrations of the visible solar surface are essential in the development of local helioseismology. We are now in a position to transfer the seismic methods that have traditionally been used to study the Earth's interior to solar investigations. This interdisciplinary approach to developing seismic imaging techniques is opening up new ways of understanding the flow and other structural characteristics beneath sunspots. In this article, I review recent progress in the imaging of sunspots and the surrounding solar active regions. By highlighting the strengths of seismic methods and the challenges facing local helioseismology, I discuss some of the new research directions and possibilities that have arisen from this novel type of seismic imaging.

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Two classes of eruptive events during Solar Minimum

10.5194/egusphere-egu21-6760 ◽

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>

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Numerical Simulations of Large-scale Solar Magnetic Fields

Australian Journal of Physics ◽

10.1071/ph850999 ◽

1985 ◽

Vol 38 (6) ◽

pp. 999 ◽

Cited By ~ 24

Author(s):

CR DeVore ◽

NR Sheeley Jr ◽

JP Boris ◽

TR Young Jr ◽

KL Harvey

Keyword(s):

Magnetic Field ◽

Magnetic Flux ◽

Large Scale ◽

Sunspot Cycle ◽

Active Regions ◽

The Sun ◽

Solar Magnetic Fields ◽

Field Patterns ◽

Large Scale Magnetic Field ◽

The Magnetic Field

We have solved numerically a transport equation which describes the evolution of the large-scale magnetic field of the Sun. Data derived from solar magnetic observations are used to initialize the computations and to account for the emergence of new magnetic flux during the sunspot cycle. Our objective is to assess the ability of the model to reproduce the observed evolution of the field patterns. We discuss recent results from simulations of individual active regions over a few solar rotations and of the magnetic field of the Sun over sunspot cycle 21.

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Investigation of Spatially Unresolved Magnetic Field Outside Sunspots Using Hinode/SOT Observations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316013016 ◽

2016 ◽

Vol 12 (S325) ◽

pp. 59-62

Author(s):

Olga Botygina ◽

Mykola Gordovskyy ◽

Vsevolod Lozitsky

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Magnetic Flux ◽

Zeeman Effect ◽

Active Regions ◽

Line Ratio ◽

Optical Telescope ◽

Flux Tubes ◽

Magnetic Flux Tubes ◽

The Magnetic Field

AbstractThe structure of photospheric magnetic fields outside sunspots is investigated in three active regions using Hinode/Solar Optical Telescope(SOT) observations. We analyze Zeeman effect in FeI 6301.5 and FeI 6302.5 lines and determine the observed magnetic field value Beff for each of them. We find that the line ratio Beff(6301)/Beff(6302) is close to 1.3 in the range Beff < 0.2 kG, and close to 1.0 for 0.8 kG < Beff < 1.2 kG. We find that the observed magnetic field is formed by flux tubes with the magnetic field strengths 1.3 − 2.3 kG even in places with weak observed magnetic field fluxes. We also estimate the diameters of smallest magnetic flux tubes to be 15 − 20 km.

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Preliminary design of the INPE's Solar Vector Magnetograph

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315004767 ◽

2014 ◽

Vol 10 (S305) ◽

pp. 195-199 ◽

Cited By ~ 1

Author(s):

L. E. A. Vieira ◽

A. L. Clúa de Gonzalez ◽

A. Dal Lago ◽

C. Wrasse ◽

E. Echer ◽

...

Keyword(s):

Magnetic Field ◽

Visible Light ◽

Solar Surface ◽

Solar Physics ◽

Solar Photosphere ◽

Preliminary Design ◽

Nearby Star ◽

Surface Magnetic Field ◽

Starting Point ◽

The Magnetic Field

AbstractWe describe the preliminary design of a magnetograph and visible-light imager instrument to study the solar dynamo processes through observations of the solar surface magnetic field distribution. The instrument will provide measurements of the vector magnetic field and of the line-of-sight velocity in the solar photosphere. As the magnetic field anchored at the solar surface produces most of the structures and energetic events in the upper solar atmosphere and significantly influences the heliosphere, the development of this instrument plays an important role in reaching the scientific goals of The Atmospheric and Space Science Coordination (CEA) at the Brazilian National Institute for Space Research (INPE). In particular, the CEA's space weather program will benefit most from the development of this technology. We expect that this project will be the starting point to establish a strong research program on Solar Physics in Brazil. Our main aim is acquiring progressively the know-how to build state-of-the-art solar vector magnetograph and visible-light imagers for space-based platforms to contribute to the efforts of the solar-terrestrial physics community to address the main unanswered questions on how our nearby Star works.

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The Emergence of Magnetic Flux in Active Regions

Symposium - International Astronomical Union ◽

10.1017/s0074180900219153 ◽

2001 ◽

Vol 203 ◽

pp. 225-228

Author(s):

W. P. Abbett ◽

G. H. Fisher ◽

Y. Fan

Keyword(s):

Magnetic Flux ◽

Flux Tube ◽

Active Regions ◽

Large Degree ◽

Solar Interior ◽

Magnetic Flux Tube ◽

Initial Field ◽

Flux Tubes ◽

Mhd Simulations ◽

Magnetic Flux Tubes

Over the past decade, “thin flux tube” models have proven successful in explaining many properties of active regions in terms of magnetic flux tube dynamics in the solar interior. On the other hand, recent 2-D MHD simulations of the emergence of magnetic flux have shown that many of the assumptions adopted in the thin flux tube approximation are invalid. For example, unless the flux tubes exhibit a large degree of initial field line twist — and observations of emerging active regions suggest they do not — they will fragment (break apart) before they are able to emerge through the surface. We attempt to resolve this paradox using a number of 3-D MHD simulations (in the anelastic approximation) that describe the rise and fragmentation of twisted magnetic flux tubes. We find that the degree of fragmentation of an evolving Ω-loop depends strongly on the 3-D geometry of the loop, and that the Coriolis force plays a dynamically important role in the evolution and emergence of magnetic flux.

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