Magnetic properties on the boundary of an evolving pore

Abstract

Context. Analyses of magnetic properties on umbrae boundaries led to the Jurcak criterion, which states that umbra-penumbra boundaries in stable sunspots are equally defined by a constant value of the vertical magnetic field, Bver_crit, and by 0.5 continuum intensity of the quiet Sun, Iqs. Umbrae with vertical magnetic fields stronger than Bver_crit are stable, whereas umbrae with vertical magnetic fields weaker than Bver_crit are unstable and prone to vanishing. Aims. To investigate the existence of a critical value of the vertical magnetic field on a pore boundary and its role in the evolution of the magnetic structure. Methods. We analysed SDO/HMI vector field maps corrected for scattered light with a temporal cadence of 12 min during a 26.5-hour period. An intensity threshold (Ic = 0.55 Iqs) is used to define the pore boundary and temporal evolutions of the magnetic properties are studied there. Results. We observe stages in the pore evolution: (1)during an initial formation phase, total magnetic field strength (B) and vertical magnetic field (Bver) increase to their maximum values of ~1920 G and ~1730 G, respectively; (2)then the pore reaches a stable phase; (3)in a second formation phase, the pore undergoes a rapid growth in size, along with a decrease in B and Bver on its boundary. In the newly formed area, Bver remains mostly below 1731 G and B remains everywhere below 1921 G; (4)ultimately, pore decay starts. We find overall that pore areas with Bver<1731 G, or equivalently B<1921 G, disintegrate faster than regions that fulfil this criteria. Conclusions. The most stable regions of the pore, similarly to the case of umbral boundaries, are defined by a critical value of Bver that is comparable to that found in stable sunspots. In addition, in this case study, the same pore areas can be similarly well-defined by a critical value of the total magnetic field strength.

7 pages, 4 figures, final version published by A&A. Solved issue with coordinates

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Cited by in corpus (5)

• The European Solar Telescope
• Characterization of magneto-convection in sunspots -- The Gough & Tayler stability criterion in MURaM sunspot simulations
• The Decay of Two Adjacent Sunspots Associated with Moving Magnetic Features
• The MODEST catalog of depth-dependent spatially coupled inversions of sunspots observed by Hinode/SOT-SP
• Exploring magnetic field properties at the boundary of solar pores: A comparative study based on SDO-HMI observations