Magnetic and velocity fields of a solar pore (original) (raw)

Properties of Magnetic and Velocity Fields in and around Solar Pores

The Astrophysical Journal, 2003

We studied the magnetic and velocity fields of four pores situated close to the disk center and its surrounding regions. We find the following results from our analysis: The velocity inside the pore is very close to zero, whereas there is a strong and narrow downflow around the pore. The vertical velocity gradient observed at the edge of the pore is stronger than the velocity gradient seen in intergranular lanes. Immediately surrounding these narrow downflows, normal granular convection is observed. This observation is consistent with the theoretical picture of an isolated flux tube embedded in a quiet region surrounded by a downflow driven by radiative energy losses. Needle-like structures were seen around the pore, with the head of the needle showing an upflow. The needle tail ends in the downflow surrounding the pore. Assuming the flow is horizontal in the body of the needle, the needle-like structures would represent a possible signature of circular flow system surrounding the pore. The radial extent of this observed flow system (which likely feeds the downflow around the pore) is about 10 00. A pore with relatively large fill fraction shows a small upflow in the center surrounded by the downflow, whereas a pore with small fill fraction shows downflows throughout the pore. The asymmetries of the observed Stokes V profiles and their temporal variations are studied. We find temporal variations of V-profile asymmetries observed within pores on timescales of 5 minutes.

Temporal Evolution of Fine Structures in and around Solar Pores

The Astrophysical Journal, 1999

Time series of high-resolution white-light images of six solar pores, observed in 1993 and 1995 at the Swedish Vacuum Solar Telescope (La Palma), are analyzed. The pores constitute an almost ideal laboratory in which to study the interaction of a vertical magnetic Ðeld with surrounding convective motions, without the perturbation of the inclined magnetic Ðeld in the penumbra. Umbral dots observed in a large pore are similar to those in mature umbrae, but they live longer, are brighter, and have a (D \ 8A .9) higher Ðlling factor. Granular motions in the vicinity of pores are driven by mesogranular Ñows. Motions toward the pore dominate in the 2A zone around the pore boundary, while at larger distances the granules move away from the pore. Pushed by these motions, small granules and granular fragments located close to the pore border sometimes penetrate into the pore, where they move inward as bright short-lived features very similar to umbral dots. The capture of bright features by the pore is probably a microscale manifestation of the "" turbulent erosion, ÏÏ which results in the decay of the pore. Formation of a transitory penumbra-like structure at the border of the large pore was observed simultaneously with the appearance of expanding elongated granules, separated by dark Ðlaments, in an adjacent granular Ðeld. These e †ects can be interpreted as a consequence of emerging bipolar magnetic "" loops ÏÏ caused by a temporary protrusion of opposite magnetic polarity.

High cadence spectropolarimetry of moving magnetic features observed around a pore

Context. Moving magnetic features (MMFs) are small-size magnetic elements that are seen to stream out from sunspots, generally during their decay phase. Several observational results presented in the literature suggest them to be closely related to magnetic filaments that extend from the penumbra of the parent spot. Nevertheless, few observations of MMFs streaming out from spots without penumbra have been reported. The literature still lacks analyses of the physical properties of these features. Aims. We investigate physical properties of monopolar MMFs observed around a small pore that had developed penumbra in the days preceding our observations and compare our results with those reported in the literature for features observed around sunspots.

Plasma flows and magnetic field interplay during the formation of a pore

Astronomy & Astrophysics, 2017

Aims. Recent simulations of solar magneto-convection have offered new levels of understanding of the interplay between plasma motions and magnetic fields in evolving active regions. We aim at verifying some aspects of the formation of magnetic regions derived from recent numerical studies in observational data. Methods. We studied the formation of a pore in the active region (AR) NOAA 11462. We analysed data obtained with the Interferometric Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope on April 17, 2012, consisting of full Stokes measurements of the Fe I 617.3 nm lines. Furthermore, we analysed SDO/HMI observations in the continuum and vector magnetograms derived from the Fe I 617.3 nm line data taken from April 15 to 19, 2012. We estimated the magnetic field strength and vector components and the line-of-sight (LOS) and horizontal motions in the photospheric region hosting the pore formation. We discuss our results in light of other observational studies and recent advances of numerical simulations. Results. The pore formation occurs in less than 1 h in the leading region of the AR. We observe that the evolution of the flux patch in the leading part of the AR is faster (<12 h) than the evolution (20-30 h) of the more diffuse and smaller scale flux patches in the trailing region. During the pore formation, the ratio between magnetic and dark area decreases from 5 to 2. We observe strong downflows at the forming pore boundary and diverging proper motions of plasma in the vicinity of the evolving feature that are directed towards the forming pore. The average values and trends of the various quantities estimated in the AR are in agreement with results of former observational studies of steady pores and with their modelled counterparts, as seen in recent numerical simulations of a rising-tube process. The agreement with the outcomes of the numerical studies holds for both the signatures of the flux emergence process (e.g. appearance of small-scale mixed polarity patterns and elongated granules) and the evolution of the region. The processes driving the formation of the pore are identified with the emergence of a magnetic flux concentration and the subsequent reorganization of the emerged flux, by the combined effect of velocity and magnetic field, in and around the evolving structure.

HIGH-RESOLUTION OBSERVATIONS OF SIPHON FLOWS IN A SOLAR MAGNETIC PORE

The Astrophysical Journal, 2011

We investigate signatures of siphon flows in a region around a solar magnetic pore, observed in the photosphere at μ = 0.6, during its decay phase. We analyze high-resolution Stokes spectra acquired by Hinode/Solar Optical Telescope along the Fe i pair at 630.2 nm. We determine the vector magnetic field and the line-of-sight velocity by an inversion of the full Stokes vector using the SIR code. We also analyze photospheric G-band filtergrams. We find evidence of a transient siphon (counter)flow at the edge of the pore. An arch-shaped structure is found to have upflow motions of 4 km s −1 in the footpoint with a stronger magnetic field and positive polarity, and downflows of the same order of magnitude in the footpoint with opposite polarity and a weaker magnetic field. The event is different from those reported in previous observations of the Sun's atmosphere and may represent a physical constraint for numerical models.

Moving Magnetic Features Around a Pore

The Astrophysical Journal Supplement Series, 2017

Spectropolarimetric observations from Sunrise/IMaX obtained in June 2013 are used for a statistical analysis to determine the physical properties of moving magnetic features (MMFs) observed near a pore. MMFs of the same and opposite polarity with respect to the pore are found to stream from its border at an average speed of 1.3 km s −1 and 1.2 km s −1 respectively, with mainly same-polarity MMFs found further away from the pore. MMFs of both polarities are found to harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs are blue-shifted, while same-polarity MMFs do not show any preference for up-or downflows. Most of the MMFs are found to be of sub-arcsecond size and carry a mean flux of ∼ 1.2×10 17 Mx.

Tiny Pores Observed by Hinode /Solar Optical Telescope

The Astrophysical Journal, 2010

The study of pores, small penumbraless sunspots, can give us a chance to understand how strong magnetic fields interact with convective motions in the photosphere. For a better understanding of this interaction, we investigate the temporal variation of several tiny pores smaller than 2. These pores were observed by the Solar Optical Telescope on board Hinode on 2006 December 29. We have analyzed the high-resolution spectropolarimetric (SP) data and the G-band filtergrams taken during the observation. Magnetic flux density and Doppler velocities of the pores are estimated by applying the center-of-gravity method to the SP data. The horizontal motions in and around the pores are tracked by adopting the nonlinear affine velocity estimator method to the G-band filter images. As a result, we found the following. (1) The darkness of the pores is positively correlated with the magnetic flux density. (2) Downflows always exist inside and around the pores. (3) The speed of downflows inside the pores is negatively correlated with their darkness. (4) The pores are surrounded by strong downflows. (5) Brightness changes of the pores are correlated with the divergence of mass flow (correlation coefficient >0.9). (6) The pores in the growing phase are associated with the converging flow pattern and the pores in the decay phase with the diverging flow pattern. Our results support the idea that a pore grows as the magnetic flux density increases due to the convergence of ambient mass flow and it decays with the decrease of the flux density due to the diverging mass flow.

Mechanisms of formation ofsolar pores and sunspots

Proceedings of the International Astronomical Union, 2012

Spontaneous formation of self-organized magnetic structures, such as sunspots and pores, is one of intriguing and oldest problems, which represents a complicated interaction of convection and magnetic fields on different scales. Observations of sunspots and pores formation reveal a fast process of accumulation of emerging magnetic field into stable long-living magnetic structures. However, the physical mechanisms of the flux accumulation into the compact magnetic structures with high field strength and their stability are not clear. Development of observational capabilities, theory, and realistic-type MHD numerical simulations open a new level of our understanding of the turbulent processes of the magnetic field accumulation. I discuss the recent progress in observations and radiative MHD simulations that provide important clues for possible mechanisms of formation and stability of sunspots and pores, and their links to the dynamo process.

On the Magnetic Nature of an Exploding Granule as Revealed by Sunrise/IMaX

The Astrophysical Journal, 2020

We study the photospheric evolution of an exploding granule observed in the quiet Sun at high spatial (∼0.″3) and temporal (31.5 s) resolution by the imaging magnetograph Sunrise/IMaX in 2009 June. These observations show that the exploding granule is cospatial to a magnetic flux emergence event occurring at mesogranular scale (up to ∼12 Mm2 area). Using a modified version of the SIR code for inverting the IMaX spectropolarimetric measurements, we obtain information about the magnetic configuration of this photospheric feature. In particular, we find evidence of highly inclined emerging fields in the structure, carrying a magnetic flux content up to ∼4 × 1018 Mx. The balance between gas and magnetic pressure in the region of flux emergence, compared with a very quiet region of the Sun, indicates that the additional pressure carried by the emerging flux increases the total pressure by about 5% and appears to allow the granulation to be modified, as predicted by numerical simulations....