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[1] Magnetic field data at 1/3 s resolution are used from the ACE spacecraft for days 7 to 33 in 2001 (Bartels rotation 2286) to characterize the statistical properties of discontinuities during this period. A method is developed for finding discontinuities independent of spread angle between magnetic fields across the discontinuity. This was viewed as necessary since larger spread angle discontinuities can occur in close proximity with smaller ones, and the smaller ones are numerous. Discontinuities are found to occur in groupings, and the separation between successive discontinuities has a distribution which is lognormal. With the expectation that most discontinuities have normals across or nearly across the magnetic field, the cross-product method is used to find the normal. Combining normal direction and plasma data from the ACE spacecraft, we find that the most probable width for discontinuities is 4 to 8 proton inertial lengths or gyroradii. For small b(ratio of proton gas and magnetic pressure), the widths scale better with proton inertial length while for large b with proton gyroradius. Most discontinuities have small changes in the total magnetic intensity and are ramp-like. The statistical properties of the discontinuities appear to come from a single population. To identify this population, rotational and tangential discontinuities and also discontinuities associated with Alfvénic turbulence are considered. The population is most consistent with turbulence.

[1] We construct a database from ACE spacecraft measurements of solar wind magnetic field fluctuations at 1 AU which resolves $2 decades in frequency at the high end of the inertial range. Using magnetic field measurements outside of magnetic clouds in combination with plasma measurements, we evaluate expressions for the Kolmogorov and Kraichnan cascade rates at 0.01 Hz from magnetic field power spectra and consider both isotropic and cross-field rates. We examine these rates as functions of proton temperature and solar wind speed, comparing them to the expected rate based on the heating of protons at 1 AU. The average Kolmogorov rate is consistently more than a factor of 10 greater than expected. We conclude that the cascade rate cannot be estimated using the Kolmogorov prescription and power spectra. The Kraichnan rate is close to the expected rate and is potentially a good way to estimate the cascade rate. No distinction is found between the isotropic and cross-field rates at 1 AU. However, consideration of the likely dependence of cascade rates with distance from the Sun shows that a distinction should exist at distances closer than 1 AU but not outside 1 AU. Moreover, we find that inside 1 AU, the cross-field Kraichnan prediction can maintain agreement with the expected heating rate whereas the isotropic prediction cannot.

[1] 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. (1998aLeamon et al. ( , 1998bLeamon et al. ( , 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 fieldaligned 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.

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