Assessment of GPS Global Ionosphere Maps over the Ocean by Comparing with TOPEX/Jason TEC measurements: A Climatological Study

Abstract

We performed a comprehensive comparison between GPS Global Ionosphere Map (GIM) and TEC measurements from TOPEX and Jason-1 satellites for the periods of 1998~2008 in order to assess the performance of the GIMs over the global ocean in particular where the GPS ground stations are very sparse. The TOPEX/Jason observations are independent and direct measurements of vertical TEC from ground to satellite altitude only over the global ocean and provide an excellent opportunity to evaluate the performance of the GIMs. Using the GIMs constructed by the Center for Orbit Determination in Europe (CODE) at University of Bern, the GIM TEC values are obtained along the TOPEX/Jason satellite orbit at the locations and times of the TEC measurements for the direct comparison between the two TECs over the ocean. Both TECs are then binned into various geophysical conditions including time of day, latitude/longitude, season, and solar and geomagnetic activities and compared each other. The result of this comparison will be presented in terms of general morphology of the global ionosphere for various geophysical conditions including the TEC variations with latitude, longitude, local time, season, solar and geomagnetic activities. In addition to the overall morphology of the ionosphere, we will also discuss about the longitudinal variations such as the Weddell Sea Anomaly and longitudinal structures of the equatorial anomaly reproduced from the two TECs.