Numerous small magnetic field discontinuities of Bartels rotation 2286 and the potential role of Alfvénic turbulence

Abstract

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 β(≡ratio of proton gas and magnetic pressure), the widths scale better with proton inertial length while for large β 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. Copyright 2007 by the American Geophysical Union.