Power spectra of the fluctuations in the solar wind

Abstract

The power spectra of the velocity, the magnetic field and the density fluctuations and their inter-relationships are investigated in the turbulent solar wind using the dimensional approach of the Kolmogorovic type. While the velocity and the magnetic field fluctuations are dynamically related within the framework of the magnetohydrodynamic (MHD) turbulence, the density fluctuations could behave as a passive scalar and be simply convected by the velocity or the magnetic field fluctuations or they could dynamically participate in the joint production mechanism of all the fluctuations. The spectrum of the density fluctuations can distinguish between these two possibilities. Further the inclusion of the Hall effect, arising from the two fluid treatment, near the ion- inertial scale generates different spectra for the velocity and the magnetic fluctuations adding steeper branches to the ideal MHD spectra. Which spectrum would the density fluctuations, behaving as a passive scalar, follow in such a case? The answer leads to the interesting consequence that the electron density fluctuations and the ion density fluctuations have different spectra at spatial scales equal to and smaller than the ion-inertial scale. This result clearly demonstrates the two fluid picture brought in by the Hall effect.