Comparison of the ionospheric peak parameters retrieved from COSMIC RO and ionosondes under geomagnetic disturbed conditions

In this paper, we present a comparison between the ionospheric peak parameters (NmF2 and hmF2) derived from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) radio occultation (RO) data and that derived from observations of ionosondes which are located in geomagnetic equatorial regions under geomagnetic disturbed conditions. In order to carry out a statistic analysis over large sample sizes, all matched pairs from COSMIC and 11 ionosonde stations between April 2006 and December 2016 under geomagnetic disturbed conditions with Kp index >3+ are studied at first. Our results demonstrate high correlations of F2 layer peak parameters obtained from the two techniques and the correlation of NmF2 is better than hmF2. We further classify the matched pairs into three groups corresponding to Kp =4, Kp=5, and Kp>=6-. It is found that as the intensity of geomagnetic activities increases, the correlation of NmF2 derived from the two techniques decreases and the relative difference of NmF2 between COSMIC and ionosondes increases. COSMIC tends to underestimate NmF2 and the amount of the underestimation increases with the increased intensity of geomagnetic activities whereas hmF2 derived from COSMIC RO are usually higher than ionosonde ones.