Magnetic helicity of global field in cycle 23

We reconstruct the magnetic helicity density of the large-scale (global) axisymmetric field of the Sun in cycle 23 using synoptic maps of magnetic field from the Michelson Doppler Imager (MDI) on board of Solar and Heliospheric Observatory (SOHO). We employ the method suggested earlier by Brandenburg et al(2003). To determine the components of the poloidal field, we use the boundary conditions typically employed in mean-field dynamo models. This allows the direct comparison of derived helicity with the predictions from the mean-field dynamo models. The axisymmetric global magnetic field exhibits positive magnetic helicity in the northern hemisphere, and negative one in the southern. This hemispheric sign asymmetry is opposite to helicity of solar active regions. The hemispheric sign asymmetry reverses during the minima of solar activity. A similar behavior is expected from the mean-field solar dynamo models. Finally, the data suggest a magnetic helicity imbalance between the northern and southern hemispheres in cycle 23. We speculate that this imbalance may affect the difference in the amplitudes of the sunspot cycle 24 in the northern and the southern hemispheres.