Resumen de World-wide analysis and modelling of the ionospheric and plasmaspheric electron contents by means of radio occultations
Yixie Shao
The research of this dissertation is studying the ionosphere by GPS radio occultation (RO) techniques. It is mainly divided into two parts.
The first part focuses on the methodology in electron density profile retrievals from RO measurements. It aims to get more precise profiles from measured data. Classic Abel inversion is a methodology widely used in RO retrievals, and the error introduced by the spherical symmetry assumption is also well recognised. Separability Method (SM) was developed to eliminate this error in previous studies. In this work, the improvement brought by SM corresponding to classic method is checked and validated. The SM does have better performance excluding the Lack of Collocation (LoC) error. The precision of the results is also shown to depend on the accuracy of the supported GIMs, i.e., the more accurate GIMs are used, the better results can be obtained. The error in SM, introduced by the mis-modelling of using the Vertical Total Electron Content (VTEC) instead of ECLEO, the electron content below LEO height, is also checked. The result shows that it has only minor impact on the retrievals.
The second part is the climatological study of topside ionosphere/bottomside plasmasphere based on the RO retrievals using SM, and aims to give a general picture of characteristics and features of these two regions in different solar periods, 2007 -- solar minimum, and 2014 – solar maximum. The empirical two-components models of topside profiles, STIP model and CPDH model, used to separate the ionospheric and plasmaspheric contribution to the VTEC measured from ground to global positioning system (GPS) satellite altitudes, are studied and validated. The conditions of applicability of the STIP model are also discussed. The same as other existing empirical models, it shows the picture of topside ionosphere till some limited altitude, which is decided by the Low Earth Orbit (LEO) satellite height used to observe the RO.
The model is used to derive transition height hu and scale height hs during these two years. Generally, hu and hs show the clear diurnal, seasonal, solar cycle dependencies. The concept of IONf, the ionospheric fractional contribution to VTEC, is introduced and studied. The ionospheric features are shown and most of the ionospheric anomalies have been analyzed through this quantity. Compared to the other ionospheric related parameters, such as Ecion and Ecpl, electron content of ionosphere and plasmasphere, IONf is more stable. Hence, it is more suitable for ionosphere modelling. The Capacitor Model is used to model the consistent ‘ionospheric charging process’ during the period of the day between sunrise and midday/afternoon. The model shows a good performance to reproduce real data in different circumstances and for the maximum and minimum solar activity years analyzed.
