The OMNI database is formed by propagating the solar wind measured at around Lagrange point L1, whose result may differ from the actual solar wind in the vicinity of the bow shock nose. To test the quality of the OMNI database, we cross-correlate the 2-hr intervals of 1-min interplanetary magnetic field (IMF) data provided mostly by ACE and WIND spacecraft with Geotail measurements in front of the bow shock (10,409 cases in 1997–2016). We used two metrics: Pearson correlation coefficient (CC) and prediction efficiency (PE). Confirming previous studies, we found that the prediction quality of actual IMF degrades continuously with increasing distance of OMNI spacecraft from the Sun-Earth line, with the amounts of poor and good predictions become nearly equal for R YZ ≥ 65 R E (they constitute ~12% of the entire database). In roughly 20% of the analyzed data, low CC and PE values were the consequence of low IMF variability (a low signal-to-noise ratio). The remaining data set includes 42% of very good data (CC ≥ 0.8), 33% of relatively good data (0.5 ≤ CC < 0.8 and PE ≥ 0), 10% of data having correct variability but wrong absolute values (0.5 ≤ CC < 0.8 and PE < 0), and 15% of poor data (CC < 0.5). We also discovered that the OMNI data are generally of a good quality when the PC index of geomagnetic activity correlates well with the solar wind-magnetosphere coupling factor suggested by Kan and Lee (1979, https://doi.org/10.1029/GL006i007p00577).
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