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• Systematic validation of the CSES RO measurements using ground-based observations. • Discovery of different error variation patterns at and near EIA crest regions. • First statistical validation results for RO EDP measurements using ISR observations. The radio occultation (RO) measurements obtained by GOR payload on board the CSES (the first China Seismo-Electromagnetic Satellite) satellite are validated using the observations from five ionosonde stations located at different latitudes and one incoherent scatter radar (ISR) observatory located at mid-latitude. CSES RO peak values (NmF2) and peak heights (hmF2) are compared with the corresponding measurements from the five ionosonde stations, and RO electron density profiles (EDP) are compared with the corresponding ISR measurements. The results show that: (1) CSES RO NmF2 measurements are generally very consistent with that from ionosondes with a correlation coefficient of 0.9448. Obvious underestimation and overestimation are shown for the daytime NmF2 measurements obtained at and near EIA (Equatorial Ionization Anomaly) crest regions, and different error variation patterns are shown: the error at the EIA peak region increases with increase of the observations, while the error at the region near the EIA crest is almost a constant. Attention should be paid to these daytime measurements obtained at and near EIA region in applications. (2) CSES RO hmF2 measurements are in good agreement with that from ionosondes with a correlation coefficient of 0.8357. There is a tendency the daytime hmF2s are overestimated and the nighttime hmF2s are underestimated. (3) CSES RO EDP measurements generally show good consistency with that from ISR measurements. The RO measurements obtained within the peak height range (200–400 km) have the best performance, but errors increase out of this altitudes range. The error for the altitude of the E layer is relatively large, therefore RO measurements are less reliable for this altitude. [ABSTRACT FROM AUTHOR]

• High correlation between data of CSES and Swarm on global scale. • High correlation on intersecting ground track probe data. • High correlation on relative relationship between nighttime and daytime data. • In situ electron density is underestimated by CSES LAP. • LAP data are available for application on relative variation studies. A preliminary validation of the in situ electron density data obtained by CSES, a newly launched electromagnetic satellite in China on Feb. 2, 2018, using the Swarm satellites LP measurements, is carried out in this study to assess the consistency and reliability of the LAP observations onboard CSES. Three ways are implemented to achieve the goal: (1) comparison of the global distribution patterns for both the daytime and nighttime data, (2) comparison of the data between CSES and Swarm at intersecting ground tracks with similar local time, and (3) comparison of the relative relationship between nighttime and daytime data using the nighttime enhancement space climatology phenomenon. The results show that the in situ electron densities estimated by LAP onboard CSES are in good agreement with data from the Swarm satellites in terms of global distributions, local details and relationship between nighttime and daytime data. A systematic bias between them is also found: LAP density estimates are much lower than that of Swarm satellites. However, the highly consistent relative variations between the two datasets proves the electron density dataset of LAP onboard CSES for now is applicable for the relative data variation applications on ionosphere-related studies. Further calibration of the LAP dataset is recommended using electron density data obtained by different measurements. [ABSTRACT FROM AUTHOR]