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| Titel |
Systematic residual ionospheric errors in radio occultation data and a potential way to minimize them |
| VerfasserIn |
J. Danzer, B. Scherllin-Pirscher, U. Foelsche |
| 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 ; 6, no. 8 ; Nr. 6, no. 8 (2013-08-29), S.2169-2179 |
| Datensatznummer |
250085047
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| Publikation (Nr.) |
 copernicus.org/amt-6-2169-2013.pdf |
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| Zusammenfassung |
| Radio occultation (RO) sensing is used to probe the earth's atmosphere in
order to obtain information about its physical properties. With a main
interest in the parameters of the neutral atmosphere, there is the need to
perform a correction of the ionospheric contribution to the bending angle.
Since this correction is an approximation to first order, there exists an
ionospheric residual, which can be expected to be larger when the ionization
is high (day versus night, high versus low solar activity). The ionospheric
residual systematically affects the accuracy of the atmospheric parameters at
low altitudes, at high altitudes (above 25–30 km) it even is an
important error source. In climate applications this could lead to a time
dependent bias which induces wrong trends in atmospheric parameters at high
altitudes. The first goal of our work was to study and characterize this
systematic residual error. In a second step we developed a simple correction
method, based purely on observational data, to reduce this residual for large
ensembles of RO profiles. In order to tackle this problem, we analyzed the
bending angle bias of CHAMP and COSMIC RO data from 2001–2011. We could
observe that the nighttime bending angle bias stays constant over the whole
period of 11 yr, while the daytime bias increases from low to high solar
activity. As a result, the difference between nighttime and daytime bias
increases from about −0.05 μrad to −0.4 μrad.
This behavior paves the way to correct the solar cycle dependent bias of daytime RO profiles. In order to test the newly developed correction method we
performed a simulation study, which allowed to separate the influence of the
ionosphere and the neutral atmosphere. Also in the simulated data we observed
a similar increase in the bias in times from low to high solar activity. In
this simulation we performed the climatological ionospheric correction of the
bending angle data, by using the bending angle bias characteristics of
a solar cycle as a correction factor. After the climatological ionospheric
correction the bias of the simulated data improved significantly, not only in
the bending angle but also in the retrieved temperature profiles. |
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