Introduction: The decay of sunspot penumbrae as part of active region evolution is an important topic related to flow fields in and around sunspots. Measurements of horizontal proper motions in sunspot penumbrae show a distinct divergence line in the middle of the penumbra. The observed outward motion in the outer penumbra is related to the Evershed flow and moving magnetic features (MMFs), which migrate to the sunspot moat. Deng et al. (2007) provided a high-resolution study of a decaying sunspot using two-dimensional spectroscopy, which showed that this divergence line still existed even after the sunspot decayed to a pore, i.e., the moat flow was still detectable. MMFs have a distinct height dependence (Choudhary and Balasubramniam 2007). In the lower atmosphere, they have a sophisticated magnetic field structure of tight low-level loops, which also show signs of twisted magnetic field lines, whereas higher in the atmosphere, the loop structure is more relaxed and closer to a potential field configuration. These mo-tions of small-scale magnetic features are embedded in the global flow fields of active regions (Choudhary et al. 2002b, Choudhary and Gosain 2003), which are either due to the pressure imbalance in two opposite polarity re-gions know as siphon flow or due to the Coriolis force, while the spots are traveling through the convection zone.
Primary Objectives: The prime objective of this HOP is to make the imaging and spectropolarimetery observations of sunspot penumbra along with the near IR observations at HeI 1083.0 nm, CaII 854.2 nm and FeI 1.5 µm line, to study the condition of penumbra formation or disappearance and the three dimensional magnetic configuration favorable for penumbral formation. |
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