Plasmaspheric Electron Content contribution inferred from ground and radio occultation derived Total Electron Content Angela Aragon Angel, Jaume Sanz, Jose Miguel Juan, Manuel Hernandez Pajares Research group of Astronomy and Geomatics Technical University of Catalonia Barcelona, Spain angela@ma4.upc.edu David Altadill Observatory del Ebro Universitat Ramon LLull Roquetes, Spain Abstract—The FORMOSAT-3/COSMIC satellite constellation has become an important source of remote sensing data globally distributed for the sounding of the atmosphere of the Earth and, in particular, the ionosphere. In this study, electron density profiles derived using the Improved Abel transform inversion in Radio Occultation (RO) scenarios are used as input data to derive some features regarding the topside and outside ionospheric contribution, hence, the plasmasphere in great extend, by means of the analysis of the integral values of the shape functions corresponding to each density profile. The novelty presented in this paper, with respect to previous works, is the use of experimental data from the FORMOSAT-3/COSMIC RO-derived electron densities to infer global characterizations and distribution of the Total Electron Content (TEC) into its main components: ionospheric TEC and plasmaspheric TEC, both contributing to TEC. The results show agreement with earlier modeled and observational data from previous local studies of the plasmaspheric contribution. The main conclusion of this research is that the plasmasphere contributes significantly to TEC and the ratio between plasmaspheric TEC and TEC has been climatologically analyzed for the whole year 2007 confirming that the major relative impact of the plasmasphere is during night time. The added value of this study is that the results obtained are globally distributed and can help to infer a proxy for the plasmaspheric contribution at any location over the globe thanks to the FORMOSAT-3/COSMIC coverage. Keywords-Ionosphere; Plasmasphere; GPS; radio occultation; electron density; TEC; Abel transform; Separability; FORMOSAT-3/COSMIC I. INTRODUCTION In the past years, many efforts have been devoted to try and successfully model the topside contribution of the ionosphere. Most of such efforts rely on the availability of global measured data provided either by direct measurements from satellite- based ionosondes on board satellite missions such as ISIS (International Satellite for Ionosphere Studies)-1, ISIS-2 [3] and IK (Intercosmos)-19 (information about this mission is to be found at http://www.astronautix.com/craft/auos.htm) or predictions based on bottom-side ionospheric measurements from ground-based ionosondes [10]. According to literature [3] [7], estimates of the contribution of the Plasmaspheric Electron Content (PEC) may vary from 10% of the Total Electron Content (TEC) during daytime hours, when the density of the F2 region is highest, to approximately 50% during night time, when the F2 region density is lowest. More recently, models based on both, TEC derived from ground receivers of signals of the Global Positioning System satellites (GPS) and ionosonde data, have proven to be able to locally reconstruct the topside ionospheric electron density contribution (e.g. [12]; [8]). The current study is focused on providing a global description for the plasmaspheric contribution based on information retrieved from electron densities derived from FORMOSAT-3/COSMIC (F-3/C) Radio Occultation (RO) data. The dense coverage of these satellite mission RO events in longitude, latitude and local time makes this constellation become a powerful tool to retrieve ionospheric and tropospheric information all time, all weather. So far, this constellation has been used to monitor the ionosphere and the troposphere, but, as it will be discussed, the interrelationship between the electron density profiles derived from ionospheric RO (IRO) and TEC will provide a way to also monitor the plasmaspheric content within the TEC. A simple model for the plasmaspheric portion within the TEC has also been implemented and able to reproduce the upper contribution of EC better. II. ELECTRON DENSITY: SEPARABILITY, EXTRAPOLATION SCHEME AND PROFILE NORMALIZATION This study is based on electron densities retrieved from F- 3/C RO data by means of the Improved Abel transform. This inversion method is based on the separability hypothesis, firstly introduced in [9]. Separability consists of the following: 978-1-4673-2493-9/12/$31.00 ©2012 IEEE 257