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| Titel |
Retrieval of temperature profiles from CHAMP for climate monitoring: intercomparison with Envisat MIPAS and GOMOS and different atmospheric analyses |
| VerfasserIn |
A. Gobiet, G. Kirchengast, G. L. Manney, M. Borsche, C. Retscher, G. Stiller |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 7, no. 13 ; Nr. 7, no. 13 (2007-07-04), S.3519-3536 |
| Datensatznummer |
250005121
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| Publikation (Nr.) |
 copernicus.org/acp-7-3519-2007.pdf |
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| Zusammenfassung |
| This study describes and evaluates a Global Navigation Satellite System
(GNSS) radio occultation (RO) retrieval scheme particularly aimed at
delivering bias-free atmospheric parameters for climate monitoring and
research. The focus of the retrieval is on the sensible use of a priori
information for careful high-altitude initialisation in order to maximise
the usable altitude range. The RO retrieval scheme has been meanwhile
applied to more than five years of data (September 2001 to present) from the
German CHAllenging Minisatellite Payload for geoscientific research (CHAMP)
satellite. In this study it was validated against various correlative
datasets including the Michelson Interferometer for Passive Atmospheric
Sounding (MIPAS) and the Global Ozone Monitoring for Occultation of Stars
(GOMOS) sensors on Envisat, five different atmospheric analyses, and the
operational CHAMP retrieval product from GeoForschungsZentrum (GFZ) Potsdam.
In the global mean within 10 to 30 km altitude we find that the present
validation observationally constrains the potential RO temperature bias to
be <0.2 K. Latitudinally resolved analyses show biases to be
observationally constrained to <0.2–0.5 K up to 35 km in most cases, and
up to 30 km in any case, even if severely biased (about 10 K or more) a
priori information is used in the high altitude initialisation of the
retrieval. No evidence is found for the 10–35 km altitude range of residual
RO bias sources other than those potentially propagated downward from
initialisation, indicating that the widely quoted RO promise of
"unbiasedness and long-term stability due to intrinsic self-calibration"
can indeed be realised given care in the data processing to strictly limit
structural uncertainty. The results thus reinforce that adequate
high-altitude initialisation is crucial for accurate stratospheric RO
retrievals. The common method of initialising, at some altitude in the upper
stratosphere, the hydrostatic integral with an upper boundary temperature or
pressure value derived from meteorological analyses is prone to introduce
biases from the upper boundary down to below 25 km. Also above 30 to 35 km,
GNSS RO delivers a considerable amount of observed information up to around
40 km, which is particularly interesting for numerical weather prediction
(NWP) systems, where direct assimilation of non-initialised observed RO
bending angles (free of a priori) is thus the method of choice. The results
underline the value of RO for climate applications. |
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