Effects of ‘Seeing’ on Vector Magnetograph Measurements

Abstract

We present a study of the effects of atmospheric seeing on quantities derived from observations of solar polarized light – specifically, the vector magnetic flux and quantities derived from its magnitude and direction. Data from the Imaging Vector Magnetograph (‘IVM’) at the U. Hawaii/Mees Solar Observatory, are degraded by various degrees by applying a blur function to the ‘incoming light’, simulating a range of seeing conditions. A quantitative study of the resulting effects on derived quantities including total magnetic flux, vertical electric current density and magnetic shear angles, are discussed as a function of the imposed degradation. The generality of the seeing effects is explored by comparing the results from two different active regions; we find that the results are comparable for those quantities directly computed from the magnetic flux vector (e.g., summed, as in total flux) but less so for those quantities involving higher-order calculations (e.g., derivatives, as in vertical currents). We suggest that for temporal series data from any instrument, a method such as that which we outline here, be applied in order to model the uncertainties imposed on the data (in addition to instrumental uncertainties, etc.) due to seeing variations.