Magnetic field depressions in the solar wind

Depressions in the interplanetary magnetic held strength occur on a wide ra nge of temporal scales, starting with magnetic holes with a duration of sev eral seconds and extending to larger-scale structures of more than 30 min d uration. Using the magnetic field measurements of the Ulysses spacecraft, w e quantify the statistical significance of the occurrence rate of depressio ns in the magnetic field compared to a lognormal distribution. On this basi s we introduce measures for the length and depth of magnetic depressions. T here is a weak indication for a change in the character of the length distr ibution at 20-40 s in the high-speed solar wind. An analysis of 115 depress ions with a length > 2 min showed that (1) they are bounded by tangential d iscontinuities in 78% of all cases, (2) normals to the structure boundaries have no strong orientation with respect to background field or global geom etry, and (3) an increased proton temperature anisotropy is the only bulk i on parameter correlating with the depressions.