Evidence of quiet-Sun chromospheric activity related to an emerging small-scale magnetic loop

Gömöry, P.; Balthasar, H.; Puschmann, K. G.

doi:10.1051/0004-6361/201321410

Cited by 5 publications

(4 citation statements)

References 41 publications

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“…We have observed a new type of granular-sized flux emergence events using high resolution spectropolarimetric measurements in the photospheric Fe I 630.2 nm lines and the chromospheric Ca II 854.2 nm line. These events differ from others reported in the literature (e.g., Centeno et al 2007;Martínez González & Bellot Rubio 2009;Gömöry et al 2010;Martínez González et al 2010;Gömöry et al 2013) in that they are not loop-shaped, but instead have a 3D semi-spherical shape, resembling a parachute. Due to their similarities we name them magnetic bubbles, as opposed to magnetic loops.…”

Section: Introductioncontrasting

confidence: 95%

Emergence of Granular-Sized Magnetic Bubbles Through the Solar Atmosphere. I. Spectropolarimetric Observations and Simulations

Ortiz

Rubio

Hansteen

et al. 2014

ApJ

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We study a granular-sized magnetic flux emergence event that occurred in NOAA 11024 in July 2009. The observations were made with the CRISP spectropolarimeter at the Swedish 1 m Solar Telescope achieving a spatial resolution of 0.14 ′′ . Simultaneous full Stokes observations of the two photospheric Fe I lines at 630.2 nm and the chromospheric Ca II 854.2 nm line allow us to describe in detail the emergence process across the solar atmosphere. We report here on 3D semi-spherical bubble events, where instead of simple magnetic footpoints, we observe complex semi-circular feet straddling a few granules. Several phenomena occur simultaneously, namely, abnormal granulation, separation of opposite-polarity legs, and brightenings at chromospheric heights. However, the most characteristic signature in these events is the observation of a dark bubble in filtergrams taken in the wings of the Ca II 854.2 nm line. There is a clear coincidence between the emergence of horizontal magnetic field patches and the formation of the dark bubble. We can infer how the bubble rises through the solar atmosphere as we see it progressing from the wings to the core of Ca II 854.2 nm. In the photosphere, the magnetic bubble shows mean upward Doppler velocities of 2 km s −1 and expands at a horizontal speed of 4 km s −1 . In about 3.5 minutes it travels some 1100 km to reach the mid chromosphere, implying an average ascent speed of 5.2 km s −1 . The maximum separation attained by the magnetic legs is 6. ′′ 6. From an inversion of the observed Stokes spectra with the SIR code we find maximum photospheric field strengths of 480 G and inclinations of nearly 90 • in the magnetic bubble interior, along with temperature deficits of up to 250 K at log τ = −2 and above. To aid the interpretation of the observations, we carry out 3D numerical simulations of the evolution of a horizontal, untwisted magnetic flux sheet injected in the convection zone, using the Bifrost code. The computational domain spans from the upper convection zone to the lower corona. In the modeled chromosphere the rising flux sheet produces a large, cool, magnetized bubble. We compare this bubble with the observed ones and find excellent agreement, including similar field strengths and velocity signals in the photosphere and chromosphere, temperature deficits, ascent speeds, expansion velocities, and lifetimes.

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Section: Introductioncontrasting

confidence: 95%

Emergence of Granular-Sized Magnetic Bubbles Through the Solar Atmosphere. I. Spectropolarimetric Observations and Simulations

Ortiz

Rubio

Hansteen

et al. 2014

ApJ

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“…We showed that the observed polarimetric signals are compatible with small-scale magnetic loops at large heliocentric angles. This detection of ubiquitous magnetic loops at the QS, together with the increasing evidence of the influence of these structures in higher layers of the solar atmosphere (Martínez González & Bellot Rubio 2009;Gömöry et al 2013), confirm the potential role of these QS structures in the energetics of the solar atmosphere (Wiegelmann et al 2010).…”

Section: Discussionsupporting

confidence: 66%

“…In the past years, several reports of observations of small-scale magnetic loops in the QS have been published (Martínez González et al 2007;Centeno et al 2007;Martínez González & Bellot Rubio 2009;Ishikawa et al 2010;Martínez González et al 2010;Gömöry et al 2010;Wiegelmann et al 2010;Martínez González et al 2011;Manso Sainz et al 2011;Martínez González et al 2012;Guglielmino et al 2012;Viticchié 2012;Gömöry et al 2013). These structures consist of two footpoints of opposite polarity that are linked by an arc-like magnetic system whose size varies from sub-arcseconds to a few arcseconds.…”

Section: Magnetic Fields That Are Incompatible With Vertical Fieldsmentioning

confidence: 99%

Magnetic topology of the north solar pole

Yabar

González

Collados

2018

A&A

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The magnetism at the poles is similar to that of the quiet Sun in the sense that no active regions are present there. However, the polar quiet Sun is somewhat different from that at the activity belt as it has a global polarity that is clearly modulated by the solar cycle. We study the polar magnetism near an activity maximum when these regions change their polarity, from which it is expected that its magnetism should be less affected by the global field. To fully characterise the magnetic field vector, we use deep full Stokes polarimetric observations of the 15 648.5 and 15 652.8 Å FeI lines. We observe the north pole as well as a quiet region at disc centre to compare their field distributions. In order to calibrate the projection effects, we observe an additional quiet region at the east limb. We find that the two limb datasets share similar magnetic field vector distributions. This means that close to a maximum, the poles look like typical limb, quiet-Sun regions. However, the magnetic field distributions at the limbs are different from the distribution inferred at disc centre. At the limbs, we infer a new population of magnetic fields with relatively strong intensities (~600−800 G), inclined by ~30° with respect to the line of sight, and with an azimuth aligned with the solar disc radial direction. This line-of-sight orientation interpreted as a single magnetic field gives rise to non-vertical fields in the local reference frame and aligned towards disc centre. This peculiar topology is very unlikely for such strong fields according to theoretical considerations. We propose that this new population at the limbs is due to the observation of unresolved magnetic loops as seen close to the limb. These loops have typical granular sizes as measured in the disc centre. At the limbs, where the spatial resolution decreases, we observe them spatially unresolved, which explains the new population of magnetic fields that is inferred. This is the first (indirect) evidence of small-scale magnetic loops outside the disc centre and would imply that these small-scale structures are ubiquitous on the entire solar surface. This result has profound implications for the energetics not only of the photosphere, but also of the outer layers since these loops have been reported to reach the chromosphere and the low corona.

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“…Observations have shown that these loops can get to the low chromosphere (Martínez González and Bellot Rubio 2009;Gömöry et al 2013). The movie presented in Fig.…”

Section: Bipolar Featuresmentioning

confidence: 93%

Quiet Sun magnetic fields: an observational view

Rubio

Suárez

2019

Living Rev Sol Phys

124

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The quiet Sun is the region of the solar surface outside of sunspots, pores, and plages. In continuum intensity it appears dominated by granular convection. However, in polarized light the quiet Sun exhibits impressive magnetic activity on a broad range of scales, from the 30,000 km of supergranular cells down to the smallest magnetic features of about 100 km resolvable with current instruments. Quiet Sun fields are observed to evolve in a coherent way, interacting with each other as they are advected by the horizontal photospheric flows. They appear and disappear over surprisingly short time scales, bringing large amounts of magnetic flux to the solar surface. For this reason they may be important contributors to the heating of the chromosphere. Peering into such fields is difficult because of the weak signals they produce, which are easily affected, and even completely hidden, by photon noise. Thus, their evolution and nature remain largely unknown. In recent years the situation has improved thanks to the advent of high-resolution, high-sensitivity spectropolarimetric measurements and the application of state-of-the-art Zeeman and Hanle effect diagnostics. Here we review this important aspect of solar magnetism, paying special attention to the techniques used to observe and characterize the fields, their evolution on the solar surface, and their physical properties as revealed by the most recent analyses. We identify the main open questions that need to be addressed in the future and offer some ideas on how to solve them.

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Evidence of quiet-Sun chromospheric activity related to an emerging small-scale magnetic loop

Cited by 5 publications

References 41 publications

Emergence of Granular-Sized Magnetic Bubbles Through the Solar Atmosphere. I. Spectropolarimetric Observations and Simulations

Emergence of Granular-Sized Magnetic Bubbles Through the Solar Atmosphere. I. Spectropolarimetric Observations and Simulations

Magnetic topology of the north solar pole

Quiet Sun magnetic fields: an observational view

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