Abstract
This paper presents the first results of a study of current helicity of the large-scale magnetic field (LSMF) using full-disk longitudinal Blong magnetograms from the Michelson Doppler Imager on board the SOHO spacecraft. We employ a known technique to reconstruct the vector magnetic field under the assumption of relatively slow evolution of the LSMF and treat the variations of Blong, occurring during a defined period of time as the result of the changing projection angle only. We compute the synoptic maps of radial (Br) and toroidal (Bλ) magnetic fields and the latitudinal profile of current helicity density hc = Br(∇ ×
)r. For eight solar rotations (1910-1917) that have been analyzed, hc shows significant variations within ±40° of solar latitude with no strong hemispheric sign asymmetry. Asymmetry is present, however, in high latitudes, where hc is negative/positive in the northern/southern hemisphere.