Abstract
Abstract This paper presents results from a study of GPS total electron content (TEC) grid maps and ionospheric electron content (IEC) over the oceans delivered by the TOPEX/Jason satellites during half a solar cycle (July 2001 to December 2008). The IEC data are averaged and binned at latitudes from 60°S to 60°N in steps of 5°±2.5°, at longitudes from 180°W to 180°E in steps of 15°±7.5°, and for 0–23 h UT in steps of 1±0.5 h UT. The ratio of monthly averaged TEC/IEC over the oceans from the observations was compared to the reference model ratio of TECm/IECm obtained using the plasmaspheric model augmented with the International Reference Ionosphere. By definition, TEC should exceed IEC by the plasmaspheric electron content (PEC) contribution at the altitude range from 1336 km (TOPEX orbit) to 20,200 km (GPS orbit). However, as solar activity tends to the minimum, we found that IEC estimates systematically exceed those of GPS TEC. An empirical scale factor was derived in terms of the smoothed sunspot number, and this factor reduced the systematic excess of the TOPEX/Jason-derived IEC over the GPS TEC by a factor of 1.5 towards the solar minimum. This factor was tested with observations made at the solar minimum and revealed that the plasmaspheric electron content to be a residual of the GPS TEC and modified TOPEX/Jason IEC.
Highlights
Total electron content (TEC) is one of the key parameters used during investigation of the Earth’s ionosphere
The proposed scaling of Topographic Experiment (TOPEX) ionospheric electron content (IEC) has been validated with the T/J measurements made during 2008, which was the year of the solar minimum of the 23rd solar cycle
Here, we compared the total electron content estimated from Global Positioning System (GPS)-derived Global Ionospheric TEC maps (GIM) maps and TOPEX/Poseidon Altimeter Satellite signals for half a solar cycle and a scale factor with the aim of accounting for the bias in T/P IEC estimates
Summary
Total electron content (TEC) is one of the key parameters used during investigation of the Earth’s ionosphere. The T/P system can provide the ionospheric electron content (IEC) for altitudes ranging from 65 to 1336 km, whereas the GPS TEC system contains contributions from both the ionosphere and the plasmasphere due to the fact that the GPS satellites are located in an orbit of 20,200 km. Knowledge of the plasmaspheric processes is relevant for applications that need to measure and model the ionosphere to altitudes much lower than that of GPS satellites, such as ground-based trans-ionospheric radars that must detect and track orbital and ballistic objects. Once the path delay is known, it is used to obtain the vertical ionospheric electron content (IEC), which is a by-product of the experiment, thereby avoiding the inherent slant to vertical conversion errors of the slant delay measurements made by the GPS satellites. With the TOPEX orbit geometry, IEC is measured over all of the oceans in the world, thereby providing data for numerous ionospheric applications
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