GLOBAL TWIST OF SUNSPOT MAGNETIC FIELDS OBTAINED FROM HIGH-RESOLUTION VECTOR MAGNETOGRAMS

Abstract

The presence of fine structures in the sunspot vector magnetic fields has\nbeen confirmed from Hinode as well as other earlier observations. We studied 43\nsunspots based on the data sets taken from ASP/DLSP, Hinode (SOT/SP) and SVM\n(USO). In this \\emph{Letter}, (i) We introduce the concept of signed shear\nangle (SSA) for sunspots and establish its importance for non force-free\nfields. (ii) We find that the sign of global $\\alpha$ (force-free parameter) is\nwell correlated with the global SSA and the photospheric chirality of sunspots.\n(iii) Local $\\alpha$ patches of opposite signs are present in the umbra of each\nsunspot. The amplitude of the spatial variation of local $\\alpha$ in the umbra\nis typically of the order of the global $\\alpha$ of the sunspot. (iv) We find\nthat the local $\\alpha$ is distributed as alternately positive and negative\nfilaments in the penumbra. The amplitude of azimuthal variation of the local\n$\\alpha$ in the penumbra is approximately an order of magnitude larger than\nthat in the umbra. The contributions of the local positive and negative\ncurrents and $\\alpha$ in the penumbra cancel each other giving almost no\ncontribution for their global values for whole sunspot. (v) Arc-like structures\n(partial rings) with a sign opposite to that of the dominant sign of $\\alpha$\nof the umbral region are seen at the umbral-penumbral boundaries of some\nsunspots. (vi) Most of the sunspots studied, belong to the minimum epoch of the\n23$^{rd}$ solar cycle and do not follow the so-called hemispheric helicity\nrule.\n