Current helicity of the large-scale photospheric magnetic field

This paper presents the first results of a study of current helicity of the large-scale magnetic held (LSMF) using full-disk longitudinal B-long magne tograms from the Michelson Doppler Imager on board the SOHO spacecraft. We employ a known technique to reconstruct the vector magnetic held under the assumption of relatively slow evolution of the LSMF and treat the variation s of B-long, occurring during a defined period of time as the result of the changing projection angle only. We compute the synoptic maps of radial (B- r) and toroidal (B-lambda) magnetic fields and the latitudinal profile of c urrent helicity density h(c) = B-r(del x B)(r). For eight solar rotations ( 1910-1917) that have been analyzed, h(c) shows significant variations withi n +/-40 degrees of solar latitude with no strong hemispheric sign asymmetry . Asymmetry is present, however, in high latitudes, where h(c) is negative/ positive in the northern/southern hemisphere.