The spatial structure of the oncoming solar wind at Earth and the shortcomings of a solar-wind monitor at L1

The mesoscale (RE to 100's of RE) magnetic field structure of the solar wind as it approaches Earth is visualized in a Y-Z (GSE) plane upstream of the Earth. The visualization is created with a modified Voronoi diagram generated to represent some of the statistical properties of the solar wind: (1) the Parker-spiral average alignment of the solar-wind magnetic flux tubes, (2) the observed variation in the orientation of the individual flux tubes about the Parker-spiral direction, and (3) the observed variability of the diameters of individual flux tubes. The flux-tube structure, the magnetic-field vector structure, and the motional-electric-field structure of the oncoming solar wind is visualized and discussed. For instance, variations in the clock angle of the solar-wind magnetic field are associated with variations in the orientations of the passing magnetic flux tubes. Using this visualization, two-spacecraft transverse-to-radial correlations of solar-wind magnetic field are discussed, as is a case of two spacecraft on two sides of the Earth seeing an extended period of very different solar-wind properties. The solar-wind visualization is also used to discuss and quantify some shortcomings of using a single solar-wind monitor at L1 to determine the temporal properties of the solar wind that will hit the Earth: those shortcomings are (1) the aberration of the solar wind, (2) the directional variability of the solar-wind velocity vector, and (3) the orbit of the monitor about the L1 point.