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| Titel |
The impact of large scale ionospheric structure on radio occultation retrievals |
| VerfasserIn |
A. J. Mannucci, C. O. Ao, X. Pi, B. A. Iijima |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 12 ; Nr. 4, no. 12 (2011-12-22), S.2837-2850 |
| Datensatznummer |
250002157
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| Publikation (Nr.) |
 copernicus.org/amt-4-2837-2011.pdf |
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| Zusammenfassung |
| We study the impact of large-scale ionospheric structure on the accuracy of
radio occultation (RO) retrievals. We use a climatological model of the
ionosphere as well as an ionospheric data assimilation model to compare
quiet and geomagnetically disturbed conditions. The presence of ionospheric
electron density gradients during disturbed conditions increases the
physical separation of the two GPS frequencies as the GPS signal traverses
the ionosphere and atmosphere. We analyze this effect in detail using
ray-tracing and a full geophysical retrieval system. During quiet
conditions, our results are similar to previously published studies. The
impact of a major ionospheric storm is analyzed using data from the 30 October 2003
"Halloween" superstorm period. At 40 km altitude, the refractivity bias
under disturbed conditions is approximately three times larger than quiet time. These results suggest the need
for ionospheric monitoring as part of an RO-based climate observation
strategy. We find that even during quiet conditions, the magnitude of
retrieval bias depends critically on assumed ionospheric electron density
structure, which may explain variations in previously published bias
estimates that use a variety of assumptions regarding large scale
ionospheric structure. We quantify the impact of spacecraft orbit altitude
on the magnitude of bending angle and retrieval error. Satellites in higher
altitude orbits (700+ km) tend to have lower residual biases due to the
tendency of the residual bending to cancel between the top and bottomside
ionosphere. Another factor affecting accuracy is the commonly-used assumption that
refractive index is unity at the receiver.
We conclude with remarks on the implications of this study for
long-term climate monitoring using RO. |
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