Magnetic holes have been studied for decades, but their three-dimensional structure has not been thoroughly investigated until now. We have identified solar wind magnetic holes observed simultaneously by the four Cluster spacecraft. By transforming the observations into a local coordinate system and identifying a principal axis, we fit the results to a three-dimensional Gaussian model to estimate their scales. We present four events that highlight the various aspects of this method, emphasizing the critical role of coordinate system selection in the analysis. The principal axis of the holes varied, and in three out of four cases, were not aligned with the magnetic field, instead forming angles between 50 and 80 degrees, suggesting that magnetic holes are not necessarily oriented along the magnetic field. Finally, our analysis reveals that the scale of the holes along one direction is significantly longer than along the other two, suggesting an elongated ellipsoid as a typical shape for their morphology.

Solar wind magnetic holes are localized depressions of the magnetic field strength, on time scales of seconds to minutes. We use Cluster multipoint measurements to identify 26 magnetic holes which are observed just upstream of the bow shock and, a short time later, downstream in the magnetosheath, thus showing that they can penetrate the bow shock and enter the magnetosheath. For two magnetic holes we show that the relation between upstream and downstream properties of the magnetic holes are well described by the MHD Rankine-Hugoniot jump conditions. We also present a small statistic investigation of the correlation between upstream and downstream observations of some properties of the magnetic holes. The temporal scale size, and magnetic field rotation across the magnetic holes are very similar for the upstream and downstream observations, while the depth of the magnetic holes varies more. The results are consistent with the interpretation that magnetic holes in Earth's and Mercury's magnetosheath are of solar wind origin, as has earlierly been suggested. Since the solar wind magnetic holes can enter the magnetosheath, they may also interact with the magnetopause, representing a new type of localised solar wind-magnetosphere interaction.