Abstract:

Over the last decade, several magnetohydrodynamic models of the solar wind proposed a two component structure for the fluctuations: a "slab" (Alfvénic) component with wavenumbers parallel to the ambient dc magnetic field and a quasi two-dimensional (turbulent) component with wavenumbers mostly perpendicular to the magnetic field. Initial support and motivation for these models was given in part from the study of three dimensional correlation functions for the magnetic field from solar wind data (W.H Matthaeus, M.L. Goldstein and D.A. Roberts 1990, JGR 95, 20673). We extend here this study to the analysis of the cross-correlation between the velocity and the magnetic field. The cross-correlation function is simply related to the cross helicity power spectrum, a quantity of great interest for solar wind models. This quantity provides, on one hand, a measure of the relative importance of outgoing and incoming Alfvénic fluctuations. On the other hand, the turbulent properties of the system are greatly influenced by the amount of cross helicity present in it. We analyze ACE data and present preliminary results for the three dimensional cross-correlation function. Special emphasis is given to the implications for solar wind models. © 2003 American Institute of Physics.