Artificial plasma cave in the low‐latitude ionosphere results from the radio occultation inversion of the FORMOSAT‐3/COSMIC

Previous studies report unexpected electron density reductions, termed “plasmacaves,” located underneath the equatorial ionization anomaly (EIA) crests. A radiooccultation (RO) observation simulation experiment has been built to evaluate possiblebiases introduced by the spherical symmetry assumption in the standard (Abel) ROinversion processes. The experiment simulates the electron density profiles andreconstructs the plasma structure of the EIA at low latitudes, where the horizontal gradientis most significant. The reconstruction shows that artificial plasma caves are createdunderneath the EIA crests along with three density enhancements in adjacent latitudes. Theartifact appears mainly below 250 km altitudes and becomes pronounced when theEIAs are well developed. Above that altitude, the two EIA features in the original (truth)model, the International Reference Ionosphere (IRI‐2007), and in the inversion are similar,but the inversion reconstructs less distinct EIA crests with underestimation of the electrondensity. A simple correction has been introduced by multiplying the ratio between thetruth and inversion with actual FORMOSAT‐3/COSMIC observations. This initialcorrection shows that the artificial plasma caves are mitigated. Results also reveal that theRO technique is not suitable to detect or rule out possible existence of the plasma caves.

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