Objectives Sporadic E (Es) layers, the thin layers with enhanced electron density sporadically appearing at the altitude range of 90 to 120 km, can cause strong fluctuations in the amplitudes measurements of global navigation satellite system (GNSS) radio occultation (RO).
Methods We use the 50 Hz signal-to-noise ratio (SNR) data of global positioning system (GPS) RO observations from the Fengyun-3C (FY3C) and Fengyun-3D (FY3D) satellites to detect the existences of Es layers, based on which the spatiotemporal distributions and seasonal variations of Es occurrences at the latitudes of 60°S-60°N during 2019-01 to 2021-12 are derived and compared.
Results It is found that the Es morphologies derived using the RO data from the two satellites independently are basically in accordance with each other, which both reflect the close relationships of the Es occurrences with the geomagnetic field and the neutral wind field. While the Es occurrences derived from FY3C are generally higher than those derived from FY3D in most seasons and over different regions, which is especially distinct in the summer season of the middle latitudes over the northern hemisphere, and the FY3C-derived Es morphology is more consistent with previous studies based on COSMIC (the constellation observing system for meteorology, lonosphere, and climate) RO data.
Conclusions Several factors should contribute to the differences between the Es morphologies derived from the RO observations of the two satellites, including the differences in the top heights of the SNR profiles, the differences in the local time coverages of the RO observations from the two satellites, and the different noise levels of the global navigation occultation sounders (GNOSs) on the two satellites. Our results indicate that the Es detection strategy might need to be adjusted according to the noise level of the GNOSs when combining the RO data from two satellites.
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