REPRODUCTION OF THE OBSERVED TWO-COMPONENT MAGNETIC HELICITY IN SOLAR WIND TURBULENCE BY A SUPERPOSITION OF PARALLEL AND OBLIQUE ALFVEN WAVES

The angular distribution of the normalized reduced magnetic helicity density (sigma(r)(m)) in solar wind turbulence reveals two components of distinct polarity in different angle ranges. This kind of two-component sigma(r)(m) m may indicate the possible wave modes and power spectral densities (PSDs) of the turbulent fluctuations. Here we model the measured angular distribution of sigma(r)(m) m by assuming a PSD distribution for Alfven fluctuations in wavevector space, and then fit the model results to the observations by adjusting the pattern of the PSD distribution. It is found that the two-component form of the PSD, which has a major and minor component close to k(perpendicular to) and k(parallel to), respectively, seems to be responsible for the observed two-component sigma(r)(m). On the other hand, both an isotropic PSD and a PSD with only a single component bending toward k(perpendicular to) fail to reproduce the observations. Moreover, it is shown that the effect of gradual balance between outward and inward wave-energy fluxes with decreasing spatial scale needs to be considered in order to reproduce the observed diminishing of vertical bar sigma(r)(m)vertical bar at shorter scales. Therefore, we suggest that the observed two-component sigma(r)(m) in the solar wind turbulence may be due to a superposition of Alfven waves with quasi-perpendicular (major part) and quasi-parallel (minor part) propagation. The waves seem to become gradually balanced toward shorter scales.