Quantifying Uncertainty in OMNI Solar Wind Measurements Projected from L 1 to the Earth's Bow Shock

Many routine measurements of the solar wind plasma and interplanetary magnetic field (IMF) are made at the L 1 Sun–Earth Lagrange point so it is helpful to characterize the errors introduced in propagating these measurements to the near-Earth environment. We have compiled over 5000 hours of plasma and magnetic field measurements (1-min averages) at two ESA Cluster satellites when they were just outside the bow shock for years 2001–2023 and compared with measurements from NASA’s OMNI measurements made near L 1 and projected to the bow shock nose. We describe a method of determining bow shock crossings and we retain only high quality instrument data, not subject to caveats. After calibrating systematic relative biases between different spacecraft instruments, empirical probability distribution functions (PDFs) of the differences between OMNI and Cluster measurements were determined and fitted by shape functions with up to five parameters. The error PDFs are heavy-tailed (with high kurtosis), with small biases, and standard deviations of: 1.5 cm -3 (proton density), 14 km s -1 (bulk speed), 0.7 nT (field magnitude), 1.2 nT (transverse field), and 41° (IMF orientation described by “clock angle”).