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| Titel |
Climatology of free-tropospheric humidity: extension into the SEVIRI era, evaluation and exemplary analysis |
| VerfasserIn |
M. Schröder, R. Roca, L. Picon, A. Kniffka, H. Brogniez |
| 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 ; 14, no. 20 ; Nr. 14, no. 20 (2014-10-23), S.11129-11148 |
| Datensatznummer |
250119114
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| Publikation (Nr.) |
 copernicus.org/acp-14-11129-2014.pdf |
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| Zusammenfassung |
A new free-tropospheric humidity (FTH) data record is presented. It is based
on observations from the Meteosat Visible and Infrared Imager (MVIRI)
onboard Meteosat-2–Meteosat-5, as well as Meteosat-7, and the Spinning
Enhanced Visible and Infrared Imager (SEVIRI) onboard Meteosat-8 and
Meteosat-9 at the water absorption band near 6.3 μm. The data set is
available under clear-sky and low-level cloud conditions. With the extension
to SEVIRI observations, the data record covers the period 1983–2009 with a
spatial resolution of 0.625° × 0.625° and a
temporal resolution of 3 h.
The FTH is the mean relative humidity (RH) in a broad layer in the free
troposphere. The relation between the observed brightness temperature (BT)
and the FTH is well established. Previous retrievals are refined by taking
into account the relative humidity Jacobians in the training process of the
statistical retrieval. The temporal coverage is extended into the SEVIRI
period, the homogenization of the BT record is improved, and the full archive
is reprocessed using updated regression coefficients.
The FTH estimated from the Meteosat observations is compared to the FTH
computed from the RH profiles of the Analyzed RadioSoundings Archive (ARSA).
An average relative bias of −3.2% and a relative root-mean-square
difference (RMSD) of 16.8% are observed. This relative RMSD agrees with
the outcome of an analysis of the total uncertainty of the FTH product. The
decadal stability of the FTH data record is 0.5 ± 0.45% per decade.
As exemplary applications, the interannual standard deviation, the
differences on decadal scales, and the linear trend in the FTH data record
and in the frequency of occurrence of FTH < 10% (FTHp10) are
analyzed per season. Interannual standard deviation maxima and maxima in
absolute decadal differences are featured in gradient areas
between dry and wet regions, as well as in areas where FTH reaches minima and
FTHp10 reaches maxima. An analysis of the FTH linear trends and of the
associated uncertainty estimates is achieved to identify possible problems
with the data record. Positive trends in FTHp10 are featured in gradient
areas between wet and dry regions, in regions where the FTH is minimum, in
regions where FTHp10 is maximum, and in regions where differences
between FTHp10 averaged over the 2000s and 1990s are negative.
However, these positive trends in FTHp10 are associated with maximum
standard deviation and are thus hardly significant. This analysis and
intercomparisons with other humidity data records are part of the Global
Energy and Water Cycle Experiment (GEWEX) Water Vapor Assessment (G-VAP). |
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