Reduced magnetic helicity behavior in different plasma regions of near-Earth space

Abstract

We present a comparative study of the scaling laws of a signed measure calculated from the reduced magnetic helicity from Cluster observations in three different near-Earth plasma regions: solar wind, foreshock, and magnetosheath. 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. We have found similar scaling properties of the reduced magnetic helicity in the solar wind and the magnetosheath; namely, there is no scale dependence at high frequency and cancellations between both polarizations continue beyond the ion cyclotron frequency. On other hand, in the foreshock we observe the prevalence of one sign of polarization, due to the presence of right-handed high-frequency waves in the plasma frame. We interpret the results in terms of the different variability in the plasma parameters and properties in the three plasma regions.