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| Titel |
CHAMP climate data based on the inversion of monthly average bending angles |
| VerfasserIn |
J. Danzer, H. Gleisner, S. B. Healy |
| 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. 12 ; Nr. 7, no. 12 (2014-12-02), S.4071-4079 |
| Datensatznummer |
250115971
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| Publikation (Nr.) |
 copernicus.org/amt-7-4071-2014.pdf |
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| Zusammenfassung |
Global Navigation Satellite System Radio Occultation (GNSS-RO) refractivity climatologies for the stratosphere can be obtained from
the Abel inversion of monthly average bending-angle profiles. The averaging of large numbers of
profiles suppresses random noise and this, in combination with simple exponential extrapolation
above an altitude of 80 km, circumvents the need for a "statistical optimization" step
in the processing. Using data from the US–Taiwanese COSMIC mission, which provides ~1500–2000
occultations per day, it has been shown that this average-profile inversion (API)
technique provides a robust method for generating stratospheric refractivity climatologies.
Prior to the launch of COSMIC in mid-2006, the data records rely on data from the CHAMP
(CHAllenging Mini-satellite Payload) mission. In order to exploit the full range of available RO data, the usage of CHAMP data is also
required. CHAMP only provided ~200 profiles per day, and the measurements were noisier than
COSMIC. As a consequence, the main research question in this study was to see if the average
bending-angle approach is also applicable to CHAMP data.
Different methods for the suppression of random noise – statistical and through data quality
prescreening – were tested. The API retrievals were compared with the more conventional
approach of averaging individual refractivity profiles, produced with the implementation of
statistical optimization used in the EUMETSAT (European Organisation for the
Exploitation of Meteorological Satellites) Radio Occultation Meteorology Satellite Application
Facility (ROM SAF) operational processing.
In this study it is demonstrated that the API retrieval technique works well for CHAMP data,
enabling the generation of long-term stratospheric RO climate data records from August 2001 and
onward. The resulting CHAMP refractivity climatologies are found to be practically identical to
the standard retrieval at the DMI (Danish Meteorological Institute) below altitudes of 35 km. Between 35 and 50 km, the differences between the two retrieval methods started to increase, showing
largest differences at high latitudes and high altitudes. Furthermore, in the winter hemisphere
high-latitude region, the biases relative to ECMWF (European Centre for Medium-range Weather Forecasts) were generally smaller for the new approach
than for the standard retrieval. |
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