scholarly journals Average surface flows before the formation of solar active regions and their relationship to the supergranulation pattern

2019 ◽  
Vol 628 ◽  
pp. A37 ◽  
Author(s):  
A. C. Birch ◽  
H. Schunker ◽  
D. C. Braun ◽  
L. Gizon
Keyword(s):  
Simple Model ◽  
Active Region ◽  
Active Regions ◽  
Convergence Region ◽  
Near Surface ◽  
Surface Flows ◽  
Quiet Sun ◽  
Horizontal Flows ◽  
Solar Active Regions ◽  
Region Emergence

Context. The emergence of solar active regions is an important but poorly understood aspect of the solar dynamo. Aims. Knowledge of the flows associated with the rise of active-region-forming magnetic concentrations through the near-surface layers will help determine the mechanisms of active region formation. Methods. We used helioseismic holography and granulation tracking to measure the horizontal flows at the surface that precede the emergence of active regions. We then averaged these flows over about sixty emerging active regions to reduce the noise, selecting active regions that emerge into relatively quiet Sun. To help interpret the results, we constructed a simple model flow field by generating synthetic “emergence locations” that are probabilistically related to the locations of supergranulation-scale convergence regions in the quiet Sun. Results. The flow maps obtained from helioseismology and granulation tracking are very similar (correlation coefficients for single maps around 0.96). We find that active region emergence is, on average, preceded by converging horizontal flows of amplitude about 40 m s−1. The convergence region extends over about 40 Mm in the east-west direction and about 20 Mm in the north-south direction and is centered in the retrograde direction relative to the emergence location. This flow pattern is largely reproduced by a model in which active region emergence occurs preferentially in the prograde direction relative to supergranulation inflows. Conclusions. Averaging over many active regions reveals a statistically significant pattern of near-surface flows prior to emergence. The qualitative success of our simple model suggests that rising flux concentrations and supergranule-scale flows interact during the emergence process.

scholarly journals Probing Surface Flows and Magnetic Activity with Time-Distance Helioseismology

2001 ◽  
Vol 203 ◽  
pp. 189-191 ◽  
Author(s):  
L. Gizon ◽  
T. L. Duvall ◽  
R. M. Larsen
Keyword(s):  
Large Scale ◽  
Active Regions ◽  
Magnetic Activity ◽  
Near Surface ◽  
Surface Flows ◽  
Time Sensitivity ◽  
Horizontal Flows ◽  
Time Distance ◽  
Radial Outflow ◽  
Sunspot Penumbra

We estimate near-surface flows using the techniques of f-mode time-distance helioseismology together with MDI/SOHO data. (1) Synoptic maps of horizontal flows are obtained for 1996, 1998 and 1999. Rotation, torsional oscillations and meridional circulation are measured. We detect weak large-scale flows converging toward active regions. Travel times are found to be shorter at locations of high magnetic activity. In addition, we measure the motion of the supergranulation pattern. (2) Realistic travel-time sensitivity kernels are used in an iterative deconvolution to infer horizontal flows at a high spatial resolution. The radial outflow outside a sunspot penumbra, called the moat, is measured.

scholarly journals Sensitivity of low-degree solar p modes to active and ephemeral regions: frequency shifts back to the Maunder minimum

2019 ◽  
Vol 489 (1) ◽  
pp. L86-L90 ◽  
Author(s):  
William J Chaplin ◽  
Rachel Howe ◽  
Sarbani Basu ◽  
Yvonne Elsworth ◽  
Timothy W Milbourne ◽  
...  
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Spatial Scales ◽  
Active Regions ◽  
Activity Cycle ◽  
Maunder Minimum ◽  
Field Frequency ◽  
Frequency Shifts ◽  
Near Surface ◽  
Low Degree

ABSTRACT We explore the sensitivity of the frequencies of low-degree solar p modes to near-surface magnetic flux on different spatial scales and strengths, specifically to active regions with strong magnetic fields and ephemeral regions with weak magnetic fields. We also use model reconstructions from the literature to calculate average frequency offsets back to the end of the Maunder minimum. We find that the p-mode frequencies are at least 3 times less sensitive (at 95  per cent confidence) to the ephemeral-region field than they are to the active-region field. Frequency shifts between activity cycle minima and maxima are controlled predominantly by the change of active region flux. Frequency shifts at cycle minima (with respect to a magnetically quiet Sun) are determined largely by the ephemeral flux, and are estimated to have been $0.1\, \rm \mu Hz$ or less over the last few minima. We conclude that at epochs of cycle minimum, frequency shifts due to near-surface magnetic activity are negligible compared to the offsets between observed and model frequencies that arise from inaccurate modelling of the near-surface layers (the so-called surface term). The implication is that this will be the case for other Sun-like stars with similar activity, which has implications for asteroseismic modelling of stars.

scholarly journals Joint Discussion 3 Solar active regions and 3D magnetic structure

2006 ◽  
Vol 2 (14) ◽  
pp. 139-168
Author(s):  
Debi Prasad Choudhary ◽  
Michal Sobotka
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Large Scale ◽  
Focal Point ◽  
Active Regions ◽  
Theoretical Modelling ◽  
Solar Chromosphere ◽  
Origin And Evolution ◽  
Solar Active Regions ◽  
The Magnetic Field

AbstractKeeping in view of the modern powerful observing tools, among othersHinode(formerlySOLAR-B),STEREOand Frequency-Agile Solar Radiotelescope, and sophisticated modelling techniques, Joint Discussion 3 during the IAU General Assembly 2006 focused on the properties of magnetic field of solar active regions starting in deep interior of the Sun, from where they buoyantly rise to the coronal heights where the site of most explosive events are located. Intimately related with the active regions, the origin and evolution of the magnetic field of quiet Sun, the large scale chromospheric structures were also the focal point of the Joint Discussion. The theoretical modelling of the generation and dynamics of magnetic field in solar convective zone show that the interaction of the magnetic field with the Coriolis force and helical turbulent convection results in the tilts and twists in the emerging flux. In the photosphere, some of these fluxes appear in sunspots with field strengths up to about 6100 G. Spectro-polarimetric measurements reveal that the line of sight velocities and magnetic field of these locations are found to be uncombed and depend on depth in the atmosphere and exhibit gradients or discontinuities. The inclined magnetic fields beyond penumbra appear as moving magnetic features that do not rise above upper photospheric heights. As the flux rises, the solar chromosphere is the most immediate and intermediary layer where competitive magnetic forces begin to dominate their thermodynamic counterparts. The magnetic field at these heights is now measured using several diagnostic lines such as CaII854.2 nm, HI656.3 nm, and HeI1083.0 nm. The radio observations show that the coronal magnetic field of post flare loops are of the order of 30 G, which might represent the force-free magnetic state of active region in the corona. The temperatures at these coronal heights, derived from the line widths, are in the range from 2.4 to 3.7 million degree. The same line profile measurements indicate the existence of asymmetric flows in the corona. The theoretical extrapolation of photospheric field into coronal heights and their comparison with the observations show that there exists a complex topology with separatrices associated to coronal null points. The interaction of these structures often lead to flares and coronal mass ejections. The current MHD modelling of active region field shows that for coronal mass ejection both local active region magnetic field and global magnetic field due to the surrounding magnetic flux are important. Here, we present an extended summary of the papers presented in Joint Discussion 03 and open questions related to the solar magnetic field that are likely to be the prime issue with the modern observing facilities such asHinodeandSTEREOmissions.

scholarly journals Transport of Magnetic Helicity and Dynamics of Solar Active Regions

2005 ◽  
Vol 13 ◽  
pp. 117-118 ◽  
Author(s):  
M. K. Georgoulis ◽  
B. J. LaBonte ◽  
D. M. Rust
Keyword(s):  
Time Series ◽  
Active Region ◽  
Lower Limit ◽  
Active Regions ◽  
Magnetic Helicity ◽  
Solar Active Regions ◽  
Linear Force

AbstractWe introduce a method to calculate the magnetic helicity density in a given active-region vector magnetogram, and a lower limit of it, based on a linear force-free (Iff) approximation. Moreover, we provide a lower limit of the total magnetic helicity in the active region (AR). A time series of magnetograms can be used to calculate the rate of helicity transport. The results can be then correlated with manifestations of the dynamical activity in ARs, such as flares and filament eruptions.

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.

scholarly journals Magnetic Helicity Propagation from Inside the Sun

2005 ◽  
Vol 13 ◽  
pp. 97-100
Author(s):  
Dana Longcope
Keyword(s):  
Active Region ◽  
Flux Tube ◽  
Convection Zone ◽  
Active Regions ◽  
Magnetic Helicity ◽  
The Sun ◽  
Solar Convection Zone ◽  
Solar Convection ◽  
Region Emergence

AbstractModels of twisted flux tube evolution provide a picture of how magnetic helicity is propagated through the solar convection zone into the corona. According to the models, helicity tends toward an approximately uniform length-density along a tube, rather than concentrating at wider portions. Coronal fields lengthen rapidly during active region emergence, requiring additional helicity to propagate from the submerged flux tube. Recent observations of emerging active regions show an evolution consistent with this prediction, and no evidence of helicity concentrating in wider sections.

scholarly journals Origine des régions actives solaires ‘anormales’

1968 ◽  
Vol 35 ◽  
pp. 25-32 ◽  
Author(s):  
M. J. Martres
Keyword(s):  
Solar Activity ◽  
Active Region ◽  
Active Center ◽  
Active Regions ◽  
The West ◽  
Magnetic Inversion ◽  
Solar Active Regions ◽  
Western Side ◽  
Magnetic Inversion Line

Solar active regions are considered ‘anomalous’ when they belong to magnetic classes γ,βγ and βf-αf. The study of the solar activity of the region where, later on, these groups are born shows an evident correlation between the presence of an old active center and the complexity of the new active region.It is found that the complexity is greater if the old active center is younger, and the superposition better. We also observe that the birth of anomalous sunspots groups occurs much more frequently on the western side of the magnetic inversion line of the old center.When the birth of an active center occurs outside and on the West of the faculae, we observe the weakly anomalous groups βf-αf. The ‘perturbation’ decreases with distance and is extended at least to 10 heliographic degrees of the boundaries of the old faculae.

scholarly journals Multifractal spectrum of solar active region NOAA 10960 in the Hα spectral line

2009 ◽  
Vol 5 (S264) ◽  
pp. 66-71 ◽  
Author(s):  
D. Batmunkh
Keyword(s):  
Active Region ◽  
Ccd Camera ◽  
Active Regions ◽  
Multifractal Spectrum ◽  
Astronomical Observatory ◽  
Active Region Noaa ◽  
Complicated Form ◽  
Multifractal Spectra ◽  
Solar Active Regions ◽  
Different Dimensions

AbstractWe obtained the Hα images of some solar active regions and prominences. Our astronomical observatory has the telescope-coronagraph which was equipped with the birefringent Halle Hα filter and CCD camera Apogee U4 (2048x2048 pixels). This paper presents multifractal spectra of images of some solar active regions in Hα line obtained with the coronagraph. The Pointwise Hoelder exponents (α) and Hausdorff spectrum fn(α) for a part of chromosphere with active region and without it, have been obtained. It is visible, that curves fn(α) for quiet and active regions of chromosphere differ very strongly. In particular, fn(α) for region with a sunspot and flare has very complicated form, and for region with filament the curves do not considerably differ from quiet chromosphere. The multifractal spectrum of quiet chromosphere shows that the quiet chromosphere is very well described by fractals with different dimensions. We analyze this result.

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