THE EFFECT OF SEEING ON SOLAR MAGNETIC-FLUX MEASUREMENTS

We investigate the influence of seeing upon measurement of magnetic fl ux of photospheric fields. For this purpose we quantify seeing variati on in one day's observation at Big Bear Solar Observatory in terms of the Fried function, a Modulation Transfer Function for the atmospheric seeing. The temporal variation of seeing quality is compared with tha t of magnetic flux measured in a quiet region with size 5' x 4' near t he solar disk center. A good correlation is found between the seeing c hange and apparent evolution of magnetic flux values, implying, as a p ossibility, that magnetic flux measurement might have been modulated b y seeing. Based on a simple model of ensembles of Gaussian magnetic el ements we argue that even the net Bur as well as the total flux can ch ange due to seeing variation if the magnetograph has a finite detectio n threshold and if the intrinsic fluxes in one and the other polaritie s are unbalanced.