Kinetic helicity of subsurface flows and magnetic flux

Abstract

We study the relation between the vorticty of solar subsurface flows and surface magnetic activity, analyzing more than five years of GONG+ data with ring-diagram analysis. We focus on the enstrophy, defined as the square of vorticity, and the kinetic helicity density, defined as the scalar product of velocity and vorticity, and derive them from the surface to a depth of about 16 Mm. We find that enstrophy and helicity density of subsurface flows are rather constant at low flux values (less than about 10 G), while at higher flux values there is a linear relation between flux and the logarithm of enstrophy or unsigned helicity. In addition, we analyze the temporal variation of thirteen emerging active regions. At the locations of these active regions, there is little enstrophy or helicity before the regions emerge, while after flux emergence the vorticity and helicity values are large. The crosscorrelation in time between flux and enstrophy shows that they are correlated and that shallow layers lag behind deeper layers. This signal might be a hint of the emergence of active regions. © 2008 IOP Publishing Ltd.