The radial distribution of magnetic helicity in the solar convective zone: Observations and dynamo theory

We continue our attempt to connect observational data on current helicity in solar active regions with solar dynamo models. In addition to our previous results about temporal and latitudinal distributions of current helicity, we argue that some information concerning the radial profile of the current helicity averaged over time, and latitude can be extracted from the available observations. The main feature of this distribution can be presented as follows. Both shallow and deep active regions demonstrate a clear dominance of one sign of current helicity in a given hemisphere during the whole cycle. Broadly speaking, current helicity has opposite polarities in the Northern and Southern hemispheres, although there are some active regions that violate this polarity rule. The relative number of active regions violating the polarity rule is significantly higher for deeper active regions. A separation of active regions into 'shallow', 'middle' and 'deep' is made by comparing their rotation rate and the helioseismic rotation law. We use a version of Parker's dynamo model in two spatial dimensions, which employs a non-linearity based on magnetic helicity conservation arguments. The predictions of this model about the radial distribution of solar current helicity appear to be in remarkable agreement with the available observational data; in particular the relative volume occupied by the current helicity of 'wrong' sign grows significantly with the depth.