Evaluating the OMNI Database: Statistical Analysis of Time-Shifted L1 Data Versus Direct Near-Earth Solar Wind Observations

This study presents a comprehensive statistical comparison of solar wind measurements between the OMNI database which contains data collected at L1 that is shifted to the bow shock nose, and near-Earth observations from MMS, Cluster, and THEMIS missions near the bow shock nose. Using a threshold-based classification methodology, the analysis encompasses approximately 353 days (MMS), 283 days (Cluster), and 125 days (THEMIS) of solar wind intervals. Bisector regression analysis reveals that the anti-sunward flow component (Formula presented.) demonstrates exceptional agreement across all missions with near-unity slopes and correlation coefficients of 0.92 for THEMIS and 0.97 for MMS and Cluster. However, perpendicular velocity components show progressively degraded performance: (Formula presented.) exhibits correlation coefficients of 0.63–0.77 with intercepts ranging from 21.57 km/s (MMS) to 47.49 km/s (THEMIS), while (Formula presented.) shows weaker correlations (0.42–0.72) with intercepts of 4.73–11.94 km/s. Ion density measurements reveal systematic mission-specific biases: MMS and THEMIS show ion density regression slopes below unity (0.59 and 0.54, respectively), while Cluster shows a slope above unity (1.14) compared to OMNI measurements. Magnetic field measurements show higher consistency, with near-unity slopes and correlation coefficients exceeding 0.84 for most components. The northward magnetic field component (Formula presented.) exhibits elevated variance ratios and reduced correlations across all missions, reaching 0.74 for THEMIS. These results quantify inherent uncertainties in cross-platform solar wind comparisons and assess the accuracy of time-shifted solar wind measurements in the OMNI database as proxies for actual near-Earth conditions, with implications for space weather applications, multispacecraft studies, and magnetohydrodynamic simulation validation requiring accurate upstream boundary conditions.