Scaling properties of the reduced magnetic helicity in the near Earth’ space

The scaling properties of the signed measure of the reduced magnetic helicity in the solar wind and in the terrestrial foreshock and magnetosheath are studied using Cluster magnetic field and plasma measurements. The reduced magnetic helicity provides information about the handedness of the magnetic field, which can be related to the polarization (left or right) of the magnetic fluctuations, once the direction of propagation with respect to the mean magnetic field is known. In the solar wind and the magnetosheath, we observe that both right- and left-handed polarizations survive to higher frequencies, beyond the ion cyclotron frequency, implying that damping mechanisms probably occur at electron scales by electron Landau resonance. In the foreshock region, however, we evidence the prevalence of one sign of polarization at higher frequencies, which we attributed to the presence of right-handed high frequency waves in plasma frame. We account for the observed differences to the variability in the plasma parameters and properties of the three plasma regions.