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| Titel |
Improving the bias characteristics of the ROPP refractivity and bending angle operators |
| VerfasserIn |
C. P. Burrows, S. B. Healy, I. D. Culverwell |
| 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 ; 7, no. 10 ; Nr. 7, no. 10 (2014-10-09), S.3445-3458 |
| Datensatznummer |
250115929
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| Publikation (Nr.) |
 copernicus.org/amt-7-3445-2014.pdf |
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| Zusammenfassung |
| The bending angle observation operator (forward model) currently used to
assimilate radio occultation (RO) data at the Met Office, the European Centre
for Medium-Range Weather Forecasts (ECMWF) and other centres is the same as
is included in the Radio Occultation Processing Package (ROPP), along with
the corresponding tangent-linear and adjoint code. The functionality of this
package will be described in another paper in this issue. The mean bending
angle innovations produced with this operator using Met Office background
fields show a bias that oscillates with height and whose magnitude peaks
between the model levels. These oscillations have been attributed to
shortcomings in the assumption of exponentially varying refractivity between
model levels. This is used directly in the refractivity operator, and
indirectly to produce forward-modelled bending angles via the Abel transform.
When the spacing between the model levels is small, this assumption is
acceptable, but at stratospheric heights where the model level spacing is
large, these biases can be significant, and can potentially degrade analyses.
This paper provides physically based improvements to the functional form of
refractivity with height. These new assumptions considerably improve the
oscillatory bias, and a number of approaches for practical implementation of
the bending angle operator are provided. |
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