Articles | Volume 35, issue 3
Regular paper
15 Mar 2017
Regular paper |  | 15 Mar 2017

High-order ionospheric effects on electron density estimation from Fengyun-3C GPS radio occultation

Junhai Li and Shuanggen Jin

Abstract. GPS radio occultation can estimate ionospheric electron density and total electron content (TEC) with high spatial resolution, e.g., China's recent Fengyun-3C GPS radio occultation. However, high-order ionospheric delays are normally ignored. In this paper, the high-order ionospheric effects on electron density estimation from the Fengyun-3C GPS radio occultation data are estimated and investigated using the NeQuick2 ionosphere model and the IGRF12 (International Geomagnetic Reference Field, 12th generation) geomagnetic model. Results show that the high-order ionospheric delays have large effects on electron density estimation with up to 800 el cm−3, which should be corrected in high-precision ionospheric density estimation and applications. The second-order ionospheric effects are more significant, particularly at 250–300 km, while third-order ionospheric effects are much smaller. Furthermore, the high-order ionospheric effects are related to the location, the local time, the radio occultation azimuth and the solar activity. The large high-order ionospheric effects are found in the low-latitude area and in the daytime as well as during strong solar activities. The second-order ionospheric effects have a maximum positive value when the radio occultation azimuth is around 0–20°, and a maximum negative value when the radio occultation azimuth is around −180 to −160°. Moreover, the geomagnetic storm also affects the high-order ionospheric delay, which should be carefully corrected.

Short summary
In this paper, we discuss the higher-order ionospheric effects on electron density estimation. We estimate the higher-order ionospheric effect carefully and obtain some conclusions. The results show that the second-order ionospheric effects cannot be ignored in precise ionospheric electron density estimation. The azimuth, the solar activity, and the occultation time and position are the main effect factors of the high-order ionospheric delay which we should consider.