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The accuracy of Milne-Eddington (ME) inversions, used to retrieve themagnetic field vector, depends upon the signal-to-noise ratio (SNR) of thespectro-polarimetric observations. The SNR in real observations varies frompixel to pixel, therefore the accuracy of the field vector also varies over themap. The aim of this work is to study the effect of polarimetric noise on theinference of magnetic field vector and the magnetic non-potentiality of a realsunspot. To this end, we use Hinode SOT/SP vector magnetogram of a real sunspotNOAA 10933 as an input to generate synthetic Stokes profiles under ME modelassumptions. We then add normally-distributed polarimetric noise of the level0.5\% of continuum intensity to these synthetic profiles and invert them againusing ME code. This process is repeated 100 times with different realizationsof noise. It is found that within most of the sunspot area (> 90% area) thespread in the (i) field strength is less than 8 Gauss, (ii) field inclinationis less than 1 degree, and (iii) field azimuth is less than 5 degrees. Further,we determine the uncertainty in the magnetic non-potentiality of a sunspot asdetermined by the force-free parameter alpha_g and Spatially Averaged SignedShear Angle (SASSA). It is found that for the sunspot studied here theseparameters are alpha_g = -3.5 +/- 0.37 (x 10^{-9} m^{-1}) and SASSA = -1.68 +/-0.014 degrees. This suggests that the SASSA is a less dispersionnon-potentiality parameter as compared to alpha_g. Further, we examine theeffect of increasing noise levels viz. 0.01, 0.1, 0.5 and 1% of continuumintensity and find that SASSA is less vulnerable to noise as compared toalpha_g parameter.

On the estimate of magnetic non-potentiality of sunspots derived using Hinode SOT/SP observations: Effect of polarimetric noise