Properties of horizontal flows inside and outside a solar pore

Roudier, Th.; Bonet, J. A.; Sobotka, M.

doi:10.1051/0004-6361:20021259

Cited by 17 publications

(37 citation statements)

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“…In this paper we call them "rosettas", a term that has been used by several authors like Sobotka et al (1999) or Roudier et al (2002). For the sake of clarity, we will define the meaning that we assign to the terms rosetta and mesogranule.…”

Section: Motions Of Granules In the Surroundings Of The Sunspotmentioning

confidence: 99%

Phase diversity restoration of sunspot images

Bonet¹,

Márquez

Müller

et al. 2005

A&A

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Abstract. Two time series, taken simultaneously in the G-band and in white-light, and corrected for telescope aberrations and turbulence perturbations using the method of phase diversity, are employed to study the motions of granules and G-band bright points (GBPs) in the moat of an old regular sunspot. Local correlation tracking and feature tracking have been utilized for this purpose. A large-scale radial outflow with a mean velocity of 0.51 km s −1 has been measured in the sunspot moat. Centres of diverging horizontal motions, identified with families of granules formed by repeatedly splitting granules, move away from the sunspot. Most of the GBPs in the moat also move outwards through radially orientated "channels" (confined between the borders of adjacent families) with velocities comparable to those of the adjacent granules. However, 6% of the GBPs move faster (>1.4 km s −1 ) than the neighbouring granules. GBPs in the moat are not regularly distributed but they are less frequent on its solar centre side.

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Section: Motions Of Granules In the Surroundings Of The Sunspotmentioning

confidence: 99%

Phase diversity restoration of sunspot images

Bonet¹,

Márquez

Müller

et al. 2005

A&A

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“…The highest velocities occur near the pores' border, where they are contaminated by convective flows penetrating from the outside. Hirzberger (2003) finds that the horizontal flow fields are asymmetric and that the absolute values of horizontal flow velocities are much smaller than the velocities reported by Roudier et al (2002). Furthermore, positive divergence structures surrounding pores are indicative of horizontal inflows, which can be explained either in terms of the continuous downflows detected in LOS velocities or by continuous explosive events in the granulation around pores.…”

Section: Introductionmentioning

confidence: 87%

“…The most conspicuous feature in the divergence map is the ring of positive divergence around the pore. Even after one-hour averaging and computing the arithmetic mean for 200 isolated pores, this ring still survives and asserts the dominance of divergence centers (Roudier et al 2002) and exploding granules (Vargas Domínguez et al 2010). …”

Section: Prototype Of An Isolated Porementioning

confidence: 96%

“…An annular structure of positive divergence (not shown) envelops the bright ring like an onion peel. The positive divergence structure contains localized divergence centers, which are related to exploding granules (see Roudier et al 2002). Pores exhibit inflows in their interior and outflows at their periphery; both are not necessarily symmetric.…”

Section: Flow Fields In and Around Isolated And Residual Poresmentioning

confidence: 99%

“…They interpret the downflow as the signature of a siphon flow (Thomas & Montesinos 1993;Montesinos & Thomas 1997) along a flux tube connecting two magnetic flux concentrations of opposite polarity. Roudier et al (2002) state that horizontal plasma velocities are smaller by a factor of two to three inside pores (see also Keil et al 1999). The highest velocities occur near the pores' border, where they are contaminated by convective flows penetrating from the outside.…”

Section: Introductionmentioning

confidence: 98%

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Horizontal flow fields observed in Hinode G-band images

Verma

Denker

2014

A&A

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Context. Solar pores are penumbra-lacking magnetic features, that mark two important transitions in the spectrum of magnetohydrodynamic processes: (1) the magnetic field becomes sufficiently strong to suppress the convective energy transport and (2) at some critical point some pores develop a penumbra and become sunspots. Aims. The purpose of this statistical study is to comprehensively describe solar pores in terms of their size, perimeter, shape, photometric properties, and horizontal proper motions. The seeing-free and uniform data of the Japanese Hinode mission provide an opportunity to compare flow fields in the vicinity of pores in different environments and at various stages of their evolution. Methods. The extensive database of high-resolution G-band images observed with the Hinode Solar Optical Telescope (SOT) is a unique resource to derive statistical properties of pores using advanced digital image processing techniques. The study is based on two data sets: (1) , when the pores migrate from high to low latitudes. Pores are rarely encountered in quiet-Sun G-band images, and only about 10% of pores exist in isolation. In general, pores do not exhibit a circular shape. Typical aspect ratios of the semi-major and -minor axes are 3:2 when ellipses are fitted to pores. Smaller pores (more than two-thirds are smaller than 5 Mm 2 ) tend to be more circular, and their boundaries are less corrugated. Both the area and perimeter length of pores obey log-normal frequency distributions. The frequency distribution of the intensity can be reproduced by two Gaussians representing dark and bright components. Bright features resembling umbral dots and even light bridges cover about 20% of the pores' area. Averaged radial profiles show a peak in the intensity at normalized radius R N = r/R pore = 2.1, followed by maxima of the divergence at R N = 2.3 and the radial component of the horizontal velocity at R N = 4.6. The divergence is negative within pores strongly suggesting converging flows towards the center of pores, whereas exterior flows are directed towards neighboring supergranular boundaries. The photometric radius of pores, where the intensity reaches quiet-Sun levels at R N = 1.4, corresponds to the position where the divergence is zero at R N = 1.6. Conclusions. Morphological and photometric properties as well as horizontal flow fields have been obtained for a statistically meaningful sample of pores. This provides critical boundary conditions for MHD simulations of magnetic flux concentrations, which eventually evolve into sunspots or just simply erode and fade away. Numerical models of pores (and sunspots) have to fit within these confines, and more importantly ensembles of pores have to agree with the frequency distributions of observed parameters.

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Solar activity II: Sunspots and pores

Sobotka

2003

Astron Nachr

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Abstract. Sunspots and pores appear as a consequence of interactions between strong magnetic fields and moving plasma. A wide variety of small-scale features, presumably of convective origin, are observed in photospheric layers of sunspots and pores: Umbral dots, light bridges, penumbral filaments, and penumbral grains. Each type of features has specific morphological, photometric, spectral, and kinematic characteristics. Spots and pores modify velocity fields in adjacent photosphere and sub-photospheric layers. Recent high-resolution spectral, broad-band, and helioseismic observations of the structure, dynamics, and magnetic fields of sunspots and pores, together with theoretical interpretations, are discussed in this review.

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Properties of horizontal flows inside and outside a solar pore

Cited by 17 publications

References 9 publications

Phase diversity restoration of sunspot images

Phase diversity restoration of sunspot images

Horizontal flow fields observed in Hinode G-band images

Solar activity II: Sunspots and pores

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