Dead Calm Areas in the Very Quiet Sun

González, M. J. Martínez; Sainz, R. Manso; Ramos, A. Asensio; Hijano, Eliot

doi:10.1088/0004-637x/755/2/175

Cited by 51 publications

(59 citation statements)

References 35 publications

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“…The lifetime of a loop is defined as the time in which a loop is recognised as two opposite polarities linked by linear polarisation. This lifetime is ∼2 min and has been derived from previous works by Martínez Bellot Rubio (2009) andMartínez González et al (2012b). This emergence rate is safely computed from raster scans when the exposure time is much shorter than the loop lifetimes.…”

Section: Observationsmentioning

confidence: 89%

Inference of magnetic fields in the very quiet Sun

González

Yabar

Lagg

et al. 2016

A&A

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Context. Over the past 20 yr, the quietest areas of the solar surface have revealed a weak but extremely dynamic magnetism occurring at small scales (<500 km), which may provide an important contribution to the dynamics and energetics of the outer layers of the atmosphere. Understanding this magnetism requires the inference of physical quantities from high-sensitivity spectro-polarimetric data with high spatio-temporal resolution. Aims. We present high-precision spectro-polarimetric data with high spatial resolution (0.4 ) of the very quiet Sun at 1.56 µm obtained with the GREGOR telescope to shed some light on this complex magnetism. Methods. We used inversion techniques in two main approaches. First, we assumed that the observed profiles can be reproduced with a constant magnetic field atmosphere embedded in a field-free medium. Second, we assumed that the resolution element has a substructure with either two constant magnetic atmospheres or a single magnetic atmosphere with gradients of the physical quantities along the optical depth, both coexisting with a global stray-light component. Results. Half of our observed quiet-Sun region is better explained by magnetic substructure within the resolution element. However, we cannot distinguish whether this substructure comes from gradients of the physical parameters along the line of sight or from horizontal gradients (across the surface). In these pixels, a model with two magnetic components is preferred, and we find two distinct magnetic field populations. The population with the larger filling factor has very weak (∼150 G) horizontal fields similar to those obtained in previous works. We demonstrate that the field vector of this population is not constrained by the observations, given the spatial resolution and polarimetric accuracy of our data. The topology of the other component with the smaller filling factor is constrained by the observations for field strengths above 250 G: we infer hG fields with inclinations and azimuth values compatible with an isotropic distribution. The filling factors are typically below 30%. We also find that the flux of the two polarities is not balanced. From the other half of the observed quiet-Sun area ∼50% are two-lobed Stokes V profiles, meaning that 23% of the field of view can be adequately explained with a single constant magnetic field embedded in a non-magnetic atmosphere. The magnetic field vector and filling factor are reliable inferred in only 50% based on the regular profiles. Therefore, 12% of the field of view harbour hG fields with filling factors typically below 30%. At our present spatial resolution, 70% of the pixels apparently are non-magnetised.

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Section: Observationsmentioning

confidence: 89%

Inference of magnetic fields in the very quiet Sun

González

Yabar

Lagg

et al. 2016

A&A

Self Cite

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“…Some observations by the Atmospheric Imaging Assembly of the Solar Dynamics Observatory, which show the details of the structures of the lower corona, show that filaments are located at the bottom of coronal cavity (e.g., Berger 2012; Régnier et al 2011). van Ballegooijen (2012) andMartínez González et al (2015). These authors studied the magnetic field in filaments, showed that helical magnetic fields surround the filaments.…”

Section: Implication To the Cme Studiesmentioning

confidence: 99%

Statistical Study of the Magnetic Field Orientation in Solar Filaments

Hanaoka

Sakurai

2017

ApJ

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We have carried out a statistical study of the average orientation of the magnetic field in solar filaments with respect to their axes for more than 400 samples, based on data taken with daily full-Sun, full-Stokes spectropolarimetric observations using the He I 1083.0 nm line. The major part of the samples are the filaments in the quiet areas, but those in the active areas are included as well. The average orientation of the magnetic field in filaments shows a systematic property depending on the hemisphere; the direction of the magnetic field in filaments in the northern (southern) hemisphere mostly deviates clockwise (counterclockwise) from their axes, which run along the magnetic polarity inversion line. The deviation angles of the magnetic field from the axes, are concentrated between 10-30• . This hemispheric pattern is consistent with that revealed for chirality of filament barbs, filament channels and for other solar features found to possess chirality. For some filaments it was confirmed that their magnetic field direction is locally parallel to their structure seen in Hα images. Our results for the first time confirmed this hemispheric pattern with the direct observation of the magnetic field in filaments. Interestingly, the filaments which show the opposite magnetic field deviation to the hemispheric pattern, are in many cases found above the polarity inversion line whose ambient photospheric magnetic field has the polarity alignment being opposite to that of active regions following the Hale-Nicholson law.

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“…For a deeper examination of the observational evidence in favour of the SSD we refer to the review by Martínez Pillet (2013). It is unclear, however, how these calm areas observed by Martínez González et al (2012b) might fit into this general framework, although they represent an important constraint on the generation and amplification of the magnetic field on small scales in the solar photosphere. Among the many possible explanations for the existence of these areas, one interesting possibility, indicated by the authors themselves, is that this might be due to the highly intermittent character of the SSD (Cattaneo & Hughes 2001), which leads to a bursty appearance of smallscale magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

Photospheric supergranular flows and magnetic flux emergence

Stangalini

2014

A&A

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A recent study carried out on high-sensitivity SUNRISE/IMAX data has reported about areas of limited flux emergence in the quiet Sun. By exploiting an independent and longer (four hours) data set acquired by Hinode/SOT, we investigate these regions in more detail by analysing their spatial distribution and relation with the supergranular flow. Our findings, while confirming these calm areas, also show that the emergence rate of small magnetic elements is largely suppressed at the locations where the divergence of the supergranular plasma flows is positive. This means that the dead-calm areas previously reported in literature are not randomly distributed across the solar photosphere, but are linked to the supergranular cells themselves. These results are discussed in the framework of the recent literature.

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Dead Calm Areas in the Very Quiet Sun

Cited by 51 publications

References 35 publications

Inference of magnetic fields in the very quiet Sun

Inference of magnetic fields in the very quiet Sun

Statistical Study of the Magnetic Field Orientation in Solar Filaments

Photospheric supergranular flows and magnetic flux emergence

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