Comparison of photospheric current helicity and subsurface kinetic helicity

Abstract

Abstract We make a comparison between photospheric current helicity and subsurface kinetic helicity in solar active regions. Four parameters are employed: average value of vertical component of current helicity density 〈Bz· (∇×B)z〉 (〈Hc〉), average force-free field factor and mean subsurface kinetic helicity 〈v· (∇×v)/|v|2〉 (αv), which is denoted as two different parameters, 〈αv1〉 and 〈αv2〉, according to different depths beneath the solar surface. A total of 38 active regions are investigated. The results show that the signs of 〈Hc〉 and αave have a typical hemispheric distribution feature. In contrast, the sign of 〈αv1〉 presents the opposite feature to the above two parameters. For 〈αv2〉, there is no obvious preponderance of the sign in each hemisphere as with the other three parameters. Although there is an opposite hemispheric preponderance between the signs of current helicity and that of kinetic helicity at 0–3 Mm beneath the solar surface, the uncertain correlations between 〈Hc〉 and 〈αv1〉, αave and 〈αv1〉, 〈Hc〉 and 〈αv2〉, and αave and 〈αv2〉 (the correlation coefficients are -0.095, 0.118, -0.102 and -0.179, respectively) do not support that the photospheric current helicity has a cause and effect relation with the kinetic helicity at 0–12 Mm beneath the solar surface.