Suppression of convection around small magnetic concentrations

Morinaga, Shin‐Ichi; Sakurai, Takashi; Ichimoto, Kiyoshi; Yokoyama, T.; Shimojo, Masataka; Katsukawa, Y.

doi:10.1051/0004-6361:20079029

Cited by 26 publications

(29 citation statements)

References 13 publications

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“…The downflow channels around the pores and SMCs were well known from previous observations (e.g. Keil et al, 1999;Nagata et al, 2008;Morinaga et al, 2008) and from numerical simulations (Cameron et al, 2007;Spruit, 1979).…”

Section: General Characteristics Of the Pore And Smcmentioning

confidence: 53%

“…For a similar reason, the filling fraction of magnetic field in a single pixel was proposed as an alternative explanation of the difference between pores and SMCs (Knölker and Schüssler, 1988). Morinaga et al (2008) reported that the filling factor of pores (0.8 -0.9) is bigger than that of G-band bright points (0.6). We have estimated the mean filling factor values inside our pores by applying the Milne-Eddington (ME) inversion method (Skumanichi and Lites, 1987) to our SP data.…”

Section: General Characteristics Of the Pore And Smcmentioning

confidence: 98%

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FISS Observations of Vertical Motion of Plasma in Tiny Pores

et al. 2013

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Pores can be exploited for the understanding of the interaction between smallscale vertical magnetic field and the surrounding convective motions as well as the transport of mechanical energy into the chromosphere along the magnetic field. For better understanding of the physics of pores, we investigate tiny pores in a new emerging active region (AR11117) that were observed and the Ca II 8542 Å line simultaneously taken by the FISS. The coordinated observation reveals that the pores are filled with plasma which moves down slowly and are surrounded by stronger downflow in the photosphere. In the lower chromosphere, we found that the plasma flows upwards inside the pores while the plasma in the SMCs is always moving down. Our inspection of the Ca II 8542 Å line from the wing to the core shows that the upflow in the pores slows down with height and turns into downflow in the upper chromosphere while the downflow in the SMCs gains its speed. Our results are in agreement with the numerical studies which suggest that rapid cooling of the interior of the pores drives a strong downflow, which collides with the dense lower layer below and rebounds into an upflow.

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Section: General Characteristics Of the Pore And Smcmentioning

confidence: 53%

Section: General Characteristics Of the Pore And Smcmentioning

confidence: 98%

FISS Observations of Vertical Motion of Plasma in Tiny Pores

et al. 2013

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“…Title et al 1989;Narayan & Scharmer 2010). Morinaga et al (2008) and Kobel et al (2012) concluded that the high spatial density of the kG magnetic fields causes a suppression of the convection process.…”

Section: Introductionmentioning

confidence: 99%

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Buehler

Lagg

Solanki

et al. 2015

A&A

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Aims. The properties of magnetic fields forming an extended plage region in AR 10953 were investigated. Methods. Stokes spectra of the Fe I line pair at 6302 Å recorded by the spectropolarimeter aboard the Hinode satellite were inverted using the SPINOR code. The code performed a 2D spatially coupled inversion on the Stokes spectra, allowing the retrieval of gradients in optical depth within the atmosphere of each pixel, whilst accounting for the effects of the instrument's PSF. Consequently, no magnetic filling factor was needed.Results. The inversion results reveal that plage is composed of magnetic flux concentrations (MFCs) with typical field strengths of 1520 G at log(τ) = −0.9 and inclinations of 10 • −15 • . The MFCs expand by forming magnetic canopies composed of weaker and more inclined magnetic fields. The expansion and average temperature stratification of isolated MFCs can be approximated well with an empirical plage thin flux tube model. The highest temperatures of MFCs are located at their edges in all log(τ) layers. Whilst the plasma inside MFCs is nearly at rest, each is surrounded by a ring of downflows of on average 2.4 km s −1 at log(τ) = 0 and peak velocities of up to 10 km s −1 , which are supersonic. The downflow ring of an MFC weakens and shifts outwards with height, tracing the MFC's expansion. Such downflow rings often harbour magnetic patches of opposite polarity to that of the main MFC with typical field strengths below 300 G at log(τ) = 0. These opposite polarity patches are situated beneath the canopy of their main MFC. We found evidence of a strong broadening of the Stokes profiles in MFCs and particularly in the downflow rings surrounding MFCs (expressed by a microturbulence in the inversion). This indicates the presence of strong unresolved velocities. Larger magnetic structures such as sunspots cause the field of nearby MFCs to be more inclined.

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“…In this paper, we bridge the gap between the works of Morinaga et al (2008) and Hagenaar et al (2008) and investigate the spatial relationship between existing strong-field regions and the detection of new magnetic features, which we take as a proxy for dynamo action, at intermediate spatial scales. We focus on the areas around supergranular network flux concentrations, and analyze whether the rate of feature birth at a range of distances from the network concentration (NC) is significantly larger or smaller than would be expected from a random distribution of events.…”

Section: Outlinementioning

confidence: 99%

“…While the cancellation events have been studied for decades, the suppression of the continued generation of magnetic flux (apart from sunspots) is less extensively studied. Two relatively recent examples include the work of Morinaga et al (2008), in which convection (and thus, presumably, dynamo action) was reduced in the presence of small-scale magnetic features such as G-band bright points, and the work of Hagenaar et al (2008), in which the emergence rate of large-scale ephemeral regions was found to be reduced in areas of strong unipolar magnetic fields (including, but not limited to, coronal holes).…”

Section: Introductionmentioning

confidence: 99%

Spatial Nonlocality of the Small-Scale Solar Dynamo

Lamb

Howard

DeForest

2014

ApJ

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We explore the nature of the small-scale solar dynamo by tracking magnetic features. We investigate two previously explored categories of the small-scale solar dynamo: shallow and deep. Recent modeling work on the shallow dynamo has produced a number of scenarios for how a strong network concentration can influence the formation and polarity of nearby small-scale magnetic features. These scenarios have measurable signatures, for which we test using magnetograms from the Narrowband Filter Imager (NFI) on board Hinode. We find no statistical tendency for newly formed magnetic features to cluster around or away from network concentrations, nor do we find any statistical relationship between their polarities. We conclude that there is no shallow or "surface" dynamo on the spatial scales observable by Hinode/NFI. In light of these results, we offer a scenario in which the subsurface field in a deep solar dynamo is stretched and distorted via turbulence, allowing the small-scale field to emerge at random locations on the photosphere.

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Suppression of convection around small magnetic concentrations

Cited by 26 publications

References 13 publications

FISS Observations of Vertical Motion of Plasma in Tiny Pores

FISS Observations of Vertical Motion of Plasma in Tiny Pores

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Spatial Nonlocality of the Small-Scale Solar Dynamo

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