Author:
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Aragón Ángel, María Ángeles; Liou, Y.-A.; Lee, C.-C.; Reinisch, B.W.; Hernández Pajares, Manuel; Juan Zornoza, José Miguel; Sanz Subirana, Jaume
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Abstract:
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Inversion techniques applied to GPS‐LEO radio occultation data allow the retrieval of
accurate and worldwide‐distributed refractivity profiles, which, in the case of the
ionosphere, can be converted into electron densities providing information regarding the
electron content distribution in this atmospheric region. In order to guarantee the accuracy
of the electron density retrievals, two key points should be taken into account: the
horizontal gradients of the electronic distribution and the topside electron content above
the LEO orbit. The deployment in April 2006 of the satellite Constellation Observing
System for Meteorology Ionosphere and Climate (FORMOSAT‐3/COSMIC), carrying
GPS receivers on board, provides valuable radio occultation data with global and almost
uniform coverage overcoming the sparsity of data from previous LEO missions (for
instance, GPS/MET, CHAMP, and SAC‐C). This is also one of the main limitations of
other sources providing direct observations, such as ionosondes. In this study, the
improved Abel transform inversion is used to analyze derived ionospheric electron density
profiles of the whole year 2007 in a scenario with very high electron density gradients:
The neighboring area of Jicamarca (76.9°W, 12°S, dip latitude: 1°N), Perú, located at very
low latitude and close to the geomagnetic equator, and the influence of the Appleton‐
Hartree equatorial anomaly (Davies, 1990). Moreover, different strategies to account
for the topside electron content in the occultation data inversion are compared and
discussed, taking advantage of the availability of FORMOSAT‐3/COSMIC data sets and
manually calibrated measurements from Jicamarca DPS. Statistical results show that for
the current scenario the improvements are only about 10%, evidencing that the lack of
colocation is one important source of error for the classical Abel inversion. Implications
with respect to the plasmaspheric contribution have been derived from this data set
analysis, in particular, the necessity to account for it specially when the Total Electron
Content (TEC) is small. |