Anisotropies and helicities in the solar wind inertial and dissipation ranges at 1 AU

We have constructed a database of ACE observations at 1 AU based on 960 intervals spanning the broadest possible range of solar wind conditions including magnetic clouds. Using spectral analysis of high-resolution magnetic field data we compare inertial range characteristics with properties in the measured dissipation range. We find that previous conclusions by Leamon et al. (1998a, 1998b, 1998c) are upheld: average wave vectors are more field-aligned in the dissipation range than in the inertial range, magnetic fluctuations are less transverse to the mean field in the dissipation range, and cyclotron damping plays an important but not exclusive role in the formation of the dissipation range. However, field-aligned wave vectors play a larger role in the formation of the dissipation range than was previously found. In the process we find significant contrast between these inertial range results and the conclusions of Dasso et al. (2005) who examine larger-scale fluctuations within the inertial range. Dasso et al. found a dominance of field-aligned wave vectors in the high-speed wind and a dominance of quasi-perpendicular (two-dimensional) wave vectors in low-speed winds. We find that the orientation of the wave vectors for the smallest scales within the inertial range are not organized by wind speed and that on average all samples show the same distribution of energy between perpendicular and field-aligned wave vectors. We conclude that this is due to the time required to evolve the spectrum toward a two-dimensional state where the smaller inertial range scales examined here evolve more quickly than the larger scales of earlier analysis. Likewise, we find no such organization within the dissipation range.