Topside electron density profiles observed at low latitudes by COSMIC and compared with in situ ion densities measured by C/NOFS

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Abstract
Electron density height profiles (EDPs) play critical roles in accurately tracing the propagation of radio frequency signals through the topside ionosphere. The Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites were designed to provide this information during GPS radio occultation events. However, due to the reliance of COSMIC data reduction on inverse Abel transformations, questions persist about the accuracy of its EDP products. The Communication/Navigation Outage Forecasting System (C/NOFS) satellite in a low‐inclination orbit offers new opportunities for empirically testing the accuracy of topside EDPs from COSMIC over the altitude range 400 to 800 km. We report here on the results of a feasibility study covering the interval 24–25 October 2011 in which a large magnetic storm occurred. We identified universal times when C/NOFS passed within 6° × 60° rectangles centered at the latitudes and longitudes of the tangent line for COSMIC EDPs. We also compared COSMIC EDPs with those predicted by two widely used models. Our analysis shows that during a very large fraction of the available events, ion densities measured by C/NOFS were in closer agreement with COSMIC EDPs than were model predictions at the same altitudes. We also use the COSMIC and C/NOFS data sets to assess stormtime effects on the low‐latitude ionosphere. During the main phase of the storm both local densities and vertical total electron content rose on the dayside, but decreased on the nightside. During recovery both quantities quickly reverted toward their quiet‐time levels.

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