Probing current and cross-helicity in the solar atmosphere: A challenge for theory

We review results of systematic data analysis of solar vector magnetograms and dopplergrams, for revealing average values of current helicity and twist over active regions and their systematic interpretation in the framework of dynamo theory. In anticipation of opportunities for collection of data on cross-helicity and further improvement of dynamo models with respect to account of this quantity in future, we propose here a series of dynamo models which could fit available observational data. We have shown that the cross-helicity alternates in sign with the solar cycle (so it is zero in the long time average), and it changes from negative to positive following the toroidal field. We demonstrate how it is possible to tune such models with respect to account of different effects to reproduce particular features of the observable solar magnetic fields and its helical properties. (c) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.